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1 //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass transforms simple global variables that never have their address
11 // taken.  If obviously true, it marks read/write globals as constant, deletes
12 // variables only stored to, etc.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #define DEBUG_TYPE "globalopt"
17 #include "llvm/Transforms/IPO.h"
18 #include "llvm/CallingConv.h"
19 #include "llvm/Constants.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Instructions.h"
22 #include "llvm/IntrinsicInst.h"
23 #include "llvm/Module.h"
24 #include "llvm/Operator.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Analysis/ConstantFolding.h"
27 #include "llvm/Analysis/MemoryBuiltins.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/Support/CallSite.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/GetElementPtrTypeIterator.h"
33 #include "llvm/Support/MathExtras.h"
34 #include "llvm/Support/raw_ostream.h"
35 #include "llvm/ADT/DenseMap.h"
36 #include "llvm/ADT/SmallPtrSet.h"
37 #include "llvm/ADT/SmallVector.h"
38 #include "llvm/ADT/Statistic.h"
39 #include "llvm/ADT/STLExtras.h"
40 #include <algorithm>
41 using namespace llvm;
42 
43 STATISTIC(NumMarked    , "Number of globals marked constant");
44 STATISTIC(NumUnnamed   , "Number of globals marked unnamed_addr");
45 STATISTIC(NumSRA       , "Number of aggregate globals broken into scalars");
46 STATISTIC(NumHeapSRA   , "Number of heap objects SRA'd");
47 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
48 STATISTIC(NumDeleted   , "Number of globals deleted");
49 STATISTIC(NumFnDeleted , "Number of functions deleted");
50 STATISTIC(NumGlobUses  , "Number of global uses devirtualized");
51 STATISTIC(NumLocalized , "Number of globals localized");
52 STATISTIC(NumShrunkToBool  , "Number of global vars shrunk to booleans");
53 STATISTIC(NumFastCallFns   , "Number of functions converted to fastcc");
54 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
55 STATISTIC(NumNestRemoved   , "Number of nest attributes removed");
56 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
57 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
58 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
59 
60 namespace {
61   struct GlobalStatus;
62   struct GlobalOpt : public ModulePass {
getAnalysisUsage__anon15e2b1800111::GlobalOpt63     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
64     }
65     static char ID; // Pass identification, replacement for typeid
GlobalOpt__anon15e2b1800111::GlobalOpt66     GlobalOpt() : ModulePass(ID) {
67       initializeGlobalOptPass(*PassRegistry::getPassRegistry());
68     }
69 
70     bool runOnModule(Module &M);
71 
72   private:
73     GlobalVariable *FindGlobalCtors(Module &M);
74     bool OptimizeFunctions(Module &M);
75     bool OptimizeGlobalVars(Module &M);
76     bool OptimizeGlobalAliases(Module &M);
77     bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
78     bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
79     bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
80                                const SmallPtrSet<const PHINode*, 16> &PHIUsers,
81                                const GlobalStatus &GS);
82     bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
83   };
84 }
85 
86 char GlobalOpt::ID = 0;
87 INITIALIZE_PASS(GlobalOpt, "globalopt",
88                 "Global Variable Optimizer", false, false)
89 
createGlobalOptimizerPass()90 ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
91 
92 namespace {
93 
94 /// GlobalStatus - As we analyze each global, keep track of some information
95 /// about it.  If we find out that the address of the global is taken, none of
96 /// this info will be accurate.
97 struct GlobalStatus {
98   /// isCompared - True if the global's address is used in a comparison.
99   bool isCompared;
100 
101   /// isLoaded - True if the global is ever loaded.  If the global isn't ever
102   /// loaded it can be deleted.
103   bool isLoaded;
104 
105   /// StoredType - Keep track of what stores to the global look like.
106   ///
107   enum StoredType {
108     /// NotStored - There is no store to this global.  It can thus be marked
109     /// constant.
110     NotStored,
111 
112     /// isInitializerStored - This global is stored to, but the only thing
113     /// stored is the constant it was initialized with.  This is only tracked
114     /// for scalar globals.
115     isInitializerStored,
116 
117     /// isStoredOnce - This global is stored to, but only its initializer and
118     /// one other value is ever stored to it.  If this global isStoredOnce, we
119     /// track the value stored to it in StoredOnceValue below.  This is only
120     /// tracked for scalar globals.
121     isStoredOnce,
122 
123     /// isStored - This global is stored to by multiple values or something else
124     /// that we cannot track.
125     isStored
126   } StoredType;
127 
128   /// StoredOnceValue - If only one value (besides the initializer constant) is
129   /// ever stored to this global, keep track of what value it is.
130   Value *StoredOnceValue;
131 
132   /// AccessingFunction/HasMultipleAccessingFunctions - These start out
133   /// null/false.  When the first accessing function is noticed, it is recorded.
134   /// When a second different accessing function is noticed,
135   /// HasMultipleAccessingFunctions is set to true.
136   const Function *AccessingFunction;
137   bool HasMultipleAccessingFunctions;
138 
139   /// HasNonInstructionUser - Set to true if this global has a user that is not
140   /// an instruction (e.g. a constant expr or GV initializer).
141   bool HasNonInstructionUser;
142 
143   /// HasPHIUser - Set to true if this global has a user that is a PHI node.
144   bool HasPHIUser;
145 
GlobalStatus__anon15e2b1800211::GlobalStatus146   GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
147                    StoredOnceValue(0), AccessingFunction(0),
148                    HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
149                    HasPHIUser(false) {}
150 };
151 
152 }
153 
154 // SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
155 // by constants itself.  Note that constants cannot be cyclic, so this test is
156 // pretty easy to implement recursively.
157 //
SafeToDestroyConstant(const Constant * C)158 static bool SafeToDestroyConstant(const Constant *C) {
159   if (isa<GlobalValue>(C)) return false;
160 
161   for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
162        ++UI)
163     if (const Constant *CU = dyn_cast<Constant>(*UI)) {
164       if (!SafeToDestroyConstant(CU)) return false;
165     } else
166       return false;
167   return true;
168 }
169 
170 
171 /// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
172 /// structure.  If the global has its address taken, return true to indicate we
173 /// can't do anything with it.
174 ///
AnalyzeGlobal(const Value * V,GlobalStatus & GS,SmallPtrSet<const PHINode *,16> & PHIUsers)175 static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS,
176                           SmallPtrSet<const PHINode*, 16> &PHIUsers) {
177   for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
178        ++UI) {
179     const User *U = *UI;
180     if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
181       GS.HasNonInstructionUser = true;
182 
183       // If the result of the constantexpr isn't pointer type, then we won't
184       // know to expect it in various places.  Just reject early.
185       if (!isa<PointerType>(CE->getType())) return true;
186 
187       if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
188     } else if (const Instruction *I = dyn_cast<Instruction>(U)) {
189       if (!GS.HasMultipleAccessingFunctions) {
190         const Function *F = I->getParent()->getParent();
191         if (GS.AccessingFunction == 0)
192           GS.AccessingFunction = F;
193         else if (GS.AccessingFunction != F)
194           GS.HasMultipleAccessingFunctions = true;
195       }
196       if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
197         GS.isLoaded = true;
198         // Don't hack on volatile/atomic loads.
199         if (!LI->isSimple()) return true;
200       } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
201         // Don't allow a store OF the address, only stores TO the address.
202         if (SI->getOperand(0) == V) return true;
203 
204         // Don't hack on volatile/atomic stores.
205         if (!SI->isSimple()) return true;
206 
207         // If this is a direct store to the global (i.e., the global is a scalar
208         // value, not an aggregate), keep more specific information about
209         // stores.
210         if (GS.StoredType != GlobalStatus::isStored) {
211           if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(
212                                                            SI->getOperand(1))) {
213             Value *StoredVal = SI->getOperand(0);
214             if (StoredVal == GV->getInitializer()) {
215               if (GS.StoredType < GlobalStatus::isInitializerStored)
216                 GS.StoredType = GlobalStatus::isInitializerStored;
217             } else if (isa<LoadInst>(StoredVal) &&
218                        cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
219               if (GS.StoredType < GlobalStatus::isInitializerStored)
220                 GS.StoredType = GlobalStatus::isInitializerStored;
221             } else if (GS.StoredType < GlobalStatus::isStoredOnce) {
222               GS.StoredType = GlobalStatus::isStoredOnce;
223               GS.StoredOnceValue = StoredVal;
224             } else if (GS.StoredType == GlobalStatus::isStoredOnce &&
225                        GS.StoredOnceValue == StoredVal) {
226               // noop.
227             } else {
228               GS.StoredType = GlobalStatus::isStored;
229             }
230           } else {
231             GS.StoredType = GlobalStatus::isStored;
232           }
233         }
234       } else if (isa<GetElementPtrInst>(I)) {
235         if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
236       } else if (isa<SelectInst>(I)) {
237         if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
238       } else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
239         // PHI nodes we can check just like select or GEP instructions, but we
240         // have to be careful about infinite recursion.
241         if (PHIUsers.insert(PN))  // Not already visited.
242           if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
243         GS.HasPHIUser = true;
244       } else if (isa<CmpInst>(I)) {
245         GS.isCompared = true;
246       } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
247         if (MTI->isVolatile()) return true;
248         if (MTI->getArgOperand(0) == V)
249           GS.StoredType = GlobalStatus::isStored;
250         if (MTI->getArgOperand(1) == V)
251           GS.isLoaded = true;
252       } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
253         assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
254         if (MSI->isVolatile()) return true;
255         GS.StoredType = GlobalStatus::isStored;
256       } else {
257         return true;  // Any other non-load instruction might take address!
258       }
259     } else if (const Constant *C = dyn_cast<Constant>(U)) {
260       GS.HasNonInstructionUser = true;
261       // We might have a dead and dangling constant hanging off of here.
262       if (!SafeToDestroyConstant(C))
263         return true;
264     } else {
265       GS.HasNonInstructionUser = true;
266       // Otherwise must be some other user.
267       return true;
268     }
269   }
270 
271   return false;
272 }
273 
getAggregateConstantElement(Constant * Agg,Constant * Idx)274 static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
275   ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
276   if (!CI) return 0;
277   unsigned IdxV = CI->getZExtValue();
278 
279   if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
280     if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
281   } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
282     if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
283   } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) {
284     if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
285   } else if (isa<ConstantAggregateZero>(Agg)) {
286     if (StructType *STy = dyn_cast<StructType>(Agg->getType())) {
287       if (IdxV < STy->getNumElements())
288         return Constant::getNullValue(STy->getElementType(IdxV));
289     } else if (SequentialType *STy =
290                dyn_cast<SequentialType>(Agg->getType())) {
291       return Constant::getNullValue(STy->getElementType());
292     }
293   } else if (isa<UndefValue>(Agg)) {
294     if (StructType *STy = dyn_cast<StructType>(Agg->getType())) {
295       if (IdxV < STy->getNumElements())
296         return UndefValue::get(STy->getElementType(IdxV));
297     } else if (SequentialType *STy =
298                dyn_cast<SequentialType>(Agg->getType())) {
299       return UndefValue::get(STy->getElementType());
300     }
301   }
302   return 0;
303 }
304 
305 
306 /// CleanupConstantGlobalUsers - We just marked GV constant.  Loop over all
307 /// users of the global, cleaning up the obvious ones.  This is largely just a
308 /// quick scan over the use list to clean up the easy and obvious cruft.  This
309 /// returns true if it made a change.
CleanupConstantGlobalUsers(Value * V,Constant * Init)310 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
311   bool Changed = false;
312   for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
313     User *U = *UI++;
314 
315     if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
316       if (Init) {
317         // Replace the load with the initializer.
318         LI->replaceAllUsesWith(Init);
319         LI->eraseFromParent();
320         Changed = true;
321       }
322     } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
323       // Store must be unreachable or storing Init into the global.
324       SI->eraseFromParent();
325       Changed = true;
326     } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
327       if (CE->getOpcode() == Instruction::GetElementPtr) {
328         Constant *SubInit = 0;
329         if (Init)
330           SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
331         Changed |= CleanupConstantGlobalUsers(CE, SubInit);
332       } else if (CE->getOpcode() == Instruction::BitCast &&
333                  CE->getType()->isPointerTy()) {
334         // Pointer cast, delete any stores and memsets to the global.
335         Changed |= CleanupConstantGlobalUsers(CE, 0);
336       }
337 
338       if (CE->use_empty()) {
339         CE->destroyConstant();
340         Changed = true;
341       }
342     } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
343       // Do not transform "gepinst (gep constexpr (GV))" here, because forming
344       // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
345       // and will invalidate our notion of what Init is.
346       Constant *SubInit = 0;
347       if (!isa<ConstantExpr>(GEP->getOperand(0))) {
348         ConstantExpr *CE =
349           dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP));
350         if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
351           SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
352       }
353       Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
354 
355       if (GEP->use_empty()) {
356         GEP->eraseFromParent();
357         Changed = true;
358       }
359     } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
360       if (MI->getRawDest() == V) {
361         MI->eraseFromParent();
362         Changed = true;
363       }
364 
365     } else if (Constant *C = dyn_cast<Constant>(U)) {
366       // If we have a chain of dead constantexprs or other things dangling from
367       // us, and if they are all dead, nuke them without remorse.
368       if (SafeToDestroyConstant(C)) {
369         C->destroyConstant();
370         // This could have invalidated UI, start over from scratch.
371         CleanupConstantGlobalUsers(V, Init);
372         return true;
373       }
374     }
375   }
376   return Changed;
377 }
378 
379 /// isSafeSROAElementUse - Return true if the specified instruction is a safe
380 /// user of a derived expression from a global that we want to SROA.
isSafeSROAElementUse(Value * V)381 static bool isSafeSROAElementUse(Value *V) {
382   // We might have a dead and dangling constant hanging off of here.
383   if (Constant *C = dyn_cast<Constant>(V))
384     return SafeToDestroyConstant(C);
385 
386   Instruction *I = dyn_cast<Instruction>(V);
387   if (!I) return false;
388 
389   // Loads are ok.
390   if (isa<LoadInst>(I)) return true;
391 
392   // Stores *to* the pointer are ok.
393   if (StoreInst *SI = dyn_cast<StoreInst>(I))
394     return SI->getOperand(0) != V;
395 
396   // Otherwise, it must be a GEP.
397   GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
398   if (GEPI == 0) return false;
399 
400   if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
401       !cast<Constant>(GEPI->getOperand(1))->isNullValue())
402     return false;
403 
404   for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
405        I != E; ++I)
406     if (!isSafeSROAElementUse(*I))
407       return false;
408   return true;
409 }
410 
411 
412 /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
413 /// Look at it and its uses and decide whether it is safe to SROA this global.
414 ///
IsUserOfGlobalSafeForSRA(User * U,GlobalValue * GV)415 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
416   // The user of the global must be a GEP Inst or a ConstantExpr GEP.
417   if (!isa<GetElementPtrInst>(U) &&
418       (!isa<ConstantExpr>(U) ||
419        cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
420     return false;
421 
422   // Check to see if this ConstantExpr GEP is SRA'able.  In particular, we
423   // don't like < 3 operand CE's, and we don't like non-constant integer
424   // indices.  This enforces that all uses are 'gep GV, 0, C, ...' for some
425   // value of C.
426   if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
427       !cast<Constant>(U->getOperand(1))->isNullValue() ||
428       !isa<ConstantInt>(U->getOperand(2)))
429     return false;
430 
431   gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
432   ++GEPI;  // Skip over the pointer index.
433 
434   // If this is a use of an array allocation, do a bit more checking for sanity.
435   if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
436     uint64_t NumElements = AT->getNumElements();
437     ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
438 
439     // Check to make sure that index falls within the array.  If not,
440     // something funny is going on, so we won't do the optimization.
441     //
442     if (Idx->getZExtValue() >= NumElements)
443       return false;
444 
445     // We cannot scalar repl this level of the array unless any array
446     // sub-indices are in-range constants.  In particular, consider:
447     // A[0][i].  We cannot know that the user isn't doing invalid things like
448     // allowing i to index an out-of-range subscript that accesses A[1].
449     //
450     // Scalar replacing *just* the outer index of the array is probably not
451     // going to be a win anyway, so just give up.
452     for (++GEPI; // Skip array index.
453          GEPI != E;
454          ++GEPI) {
455       uint64_t NumElements;
456       if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
457         NumElements = SubArrayTy->getNumElements();
458       else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
459         NumElements = SubVectorTy->getNumElements();
460       else {
461         assert((*GEPI)->isStructTy() &&
462                "Indexed GEP type is not array, vector, or struct!");
463         continue;
464       }
465 
466       ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
467       if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
468         return false;
469     }
470   }
471 
472   for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
473     if (!isSafeSROAElementUse(*I))
474       return false;
475   return true;
476 }
477 
478 /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
479 /// is safe for us to perform this transformation.
480 ///
GlobalUsersSafeToSRA(GlobalValue * GV)481 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
482   for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
483        UI != E; ++UI) {
484     if (!IsUserOfGlobalSafeForSRA(*UI, GV))
485       return false;
486   }
487   return true;
488 }
489 
490 
491 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
492 /// variable.  This opens the door for other optimizations by exposing the
493 /// behavior of the program in a more fine-grained way.  We have determined that
494 /// this transformation is safe already.  We return the first global variable we
495 /// insert so that the caller can reprocess it.
SRAGlobal(GlobalVariable * GV,const TargetData & TD)496 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) {
497   // Make sure this global only has simple uses that we can SRA.
498   if (!GlobalUsersSafeToSRA(GV))
499     return 0;
500 
501   assert(GV->hasLocalLinkage() && !GV->isConstant());
502   Constant *Init = GV->getInitializer();
503   Type *Ty = Init->getType();
504 
505   std::vector<GlobalVariable*> NewGlobals;
506   Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
507 
508   // Get the alignment of the global, either explicit or target-specific.
509   unsigned StartAlignment = GV->getAlignment();
510   if (StartAlignment == 0)
511     StartAlignment = TD.getABITypeAlignment(GV->getType());
512 
513   if (StructType *STy = dyn_cast<StructType>(Ty)) {
514     NewGlobals.reserve(STy->getNumElements());
515     const StructLayout &Layout = *TD.getStructLayout(STy);
516     for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
517       Constant *In = getAggregateConstantElement(Init,
518                     ConstantInt::get(Type::getInt32Ty(STy->getContext()), i));
519       assert(In && "Couldn't get element of initializer?");
520       GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
521                                                GlobalVariable::InternalLinkage,
522                                                In, GV->getName()+"."+Twine(i),
523                                                GV->isThreadLocal(),
524                                               GV->getType()->getAddressSpace());
525       Globals.insert(GV, NGV);
526       NewGlobals.push_back(NGV);
527 
528       // Calculate the known alignment of the field.  If the original aggregate
529       // had 256 byte alignment for example, something might depend on that:
530       // propagate info to each field.
531       uint64_t FieldOffset = Layout.getElementOffset(i);
532       unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
533       if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
534         NGV->setAlignment(NewAlign);
535     }
536   } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
537     unsigned NumElements = 0;
538     if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
539       NumElements = ATy->getNumElements();
540     else
541       NumElements = cast<VectorType>(STy)->getNumElements();
542 
543     if (NumElements > 16 && GV->hasNUsesOrMore(16))
544       return 0; // It's not worth it.
545     NewGlobals.reserve(NumElements);
546 
547     uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
548     unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
549     for (unsigned i = 0, e = NumElements; i != e; ++i) {
550       Constant *In = getAggregateConstantElement(Init,
551                     ConstantInt::get(Type::getInt32Ty(Init->getContext()), i));
552       assert(In && "Couldn't get element of initializer?");
553 
554       GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
555                                                GlobalVariable::InternalLinkage,
556                                                In, GV->getName()+"."+Twine(i),
557                                                GV->isThreadLocal(),
558                                               GV->getType()->getAddressSpace());
559       Globals.insert(GV, NGV);
560       NewGlobals.push_back(NGV);
561 
562       // Calculate the known alignment of the field.  If the original aggregate
563       // had 256 byte alignment for example, something might depend on that:
564       // propagate info to each field.
565       unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
566       if (NewAlign > EltAlign)
567         NGV->setAlignment(NewAlign);
568     }
569   }
570 
571   if (NewGlobals.empty())
572     return 0;
573 
574   DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
575 
576   Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
577 
578   // Loop over all of the uses of the global, replacing the constantexpr geps,
579   // with smaller constantexpr geps or direct references.
580   while (!GV->use_empty()) {
581     User *GEP = GV->use_back();
582     assert(((isa<ConstantExpr>(GEP) &&
583              cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
584             isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
585 
586     // Ignore the 1th operand, which has to be zero or else the program is quite
587     // broken (undefined).  Get the 2nd operand, which is the structure or array
588     // index.
589     unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
590     if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
591 
592     Value *NewPtr = NewGlobals[Val];
593 
594     // Form a shorter GEP if needed.
595     if (GEP->getNumOperands() > 3) {
596       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
597         SmallVector<Constant*, 8> Idxs;
598         Idxs.push_back(NullInt);
599         for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
600           Idxs.push_back(CE->getOperand(i));
601         NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
602       } else {
603         GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
604         SmallVector<Value*, 8> Idxs;
605         Idxs.push_back(NullInt);
606         for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
607           Idxs.push_back(GEPI->getOperand(i));
608         NewPtr = GetElementPtrInst::Create(NewPtr, Idxs,
609                                            GEPI->getName()+"."+Twine(Val),GEPI);
610       }
611     }
612     GEP->replaceAllUsesWith(NewPtr);
613 
614     if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
615       GEPI->eraseFromParent();
616     else
617       cast<ConstantExpr>(GEP)->destroyConstant();
618   }
619 
620   // Delete the old global, now that it is dead.
621   Globals.erase(GV);
622   ++NumSRA;
623 
624   // Loop over the new globals array deleting any globals that are obviously
625   // dead.  This can arise due to scalarization of a structure or an array that
626   // has elements that are dead.
627   unsigned FirstGlobal = 0;
628   for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
629     if (NewGlobals[i]->use_empty()) {
630       Globals.erase(NewGlobals[i]);
631       if (FirstGlobal == i) ++FirstGlobal;
632     }
633 
634   return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
635 }
636 
637 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
638 /// value will trap if the value is dynamically null.  PHIs keeps track of any
639 /// phi nodes we've seen to avoid reprocessing them.
AllUsesOfValueWillTrapIfNull(const Value * V,SmallPtrSet<const PHINode *,8> & PHIs)640 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
641                                          SmallPtrSet<const PHINode*, 8> &PHIs) {
642   for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
643        ++UI) {
644     const User *U = *UI;
645 
646     if (isa<LoadInst>(U)) {
647       // Will trap.
648     } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
649       if (SI->getOperand(0) == V) {
650         //cerr << "NONTRAPPING USE: " << *U;
651         return false;  // Storing the value.
652       }
653     } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
654       if (CI->getCalledValue() != V) {
655         //cerr << "NONTRAPPING USE: " << *U;
656         return false;  // Not calling the ptr
657       }
658     } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
659       if (II->getCalledValue() != V) {
660         //cerr << "NONTRAPPING USE: " << *U;
661         return false;  // Not calling the ptr
662       }
663     } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
664       if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
665     } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
666       if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
667     } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
668       // If we've already seen this phi node, ignore it, it has already been
669       // checked.
670       if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
671         return false;
672     } else if (isa<ICmpInst>(U) &&
673                isa<ConstantPointerNull>(UI->getOperand(1))) {
674       // Ignore icmp X, null
675     } else {
676       //cerr << "NONTRAPPING USE: " << *U;
677       return false;
678     }
679   }
680   return true;
681 }
682 
683 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
684 /// from GV will trap if the loaded value is null.  Note that this also permits
685 /// comparisons of the loaded value against null, as a special case.
AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable * GV)686 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
687   for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
688        UI != E; ++UI) {
689     const User *U = *UI;
690 
691     if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
692       SmallPtrSet<const PHINode*, 8> PHIs;
693       if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
694         return false;
695     } else if (isa<StoreInst>(U)) {
696       // Ignore stores to the global.
697     } else {
698       // We don't know or understand this user, bail out.
699       //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
700       return false;
701     }
702   }
703   return true;
704 }
705 
OptimizeAwayTrappingUsesOfValue(Value * V,Constant * NewV)706 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
707   bool Changed = false;
708   for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
709     Instruction *I = cast<Instruction>(*UI++);
710     if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
711       LI->setOperand(0, NewV);
712       Changed = true;
713     } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
714       if (SI->getOperand(1) == V) {
715         SI->setOperand(1, NewV);
716         Changed = true;
717       }
718     } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
719       CallSite CS(I);
720       if (CS.getCalledValue() == V) {
721         // Calling through the pointer!  Turn into a direct call, but be careful
722         // that the pointer is not also being passed as an argument.
723         CS.setCalledFunction(NewV);
724         Changed = true;
725         bool PassedAsArg = false;
726         for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
727           if (CS.getArgument(i) == V) {
728             PassedAsArg = true;
729             CS.setArgument(i, NewV);
730           }
731 
732         if (PassedAsArg) {
733           // Being passed as an argument also.  Be careful to not invalidate UI!
734           UI = V->use_begin();
735         }
736       }
737     } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
738       Changed |= OptimizeAwayTrappingUsesOfValue(CI,
739                                 ConstantExpr::getCast(CI->getOpcode(),
740                                                       NewV, CI->getType()));
741       if (CI->use_empty()) {
742         Changed = true;
743         CI->eraseFromParent();
744       }
745     } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
746       // Should handle GEP here.
747       SmallVector<Constant*, 8> Idxs;
748       Idxs.reserve(GEPI->getNumOperands()-1);
749       for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
750            i != e; ++i)
751         if (Constant *C = dyn_cast<Constant>(*i))
752           Idxs.push_back(C);
753         else
754           break;
755       if (Idxs.size() == GEPI->getNumOperands()-1)
756         Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
757                           ConstantExpr::getGetElementPtr(NewV, Idxs));
758       if (GEPI->use_empty()) {
759         Changed = true;
760         GEPI->eraseFromParent();
761       }
762     }
763   }
764 
765   return Changed;
766 }
767 
768 
769 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
770 /// value stored into it.  If there are uses of the loaded value that would trap
771 /// if the loaded value is dynamically null, then we know that they cannot be
772 /// reachable with a null optimize away the load.
OptimizeAwayTrappingUsesOfLoads(GlobalVariable * GV,Constant * LV)773 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) {
774   bool Changed = false;
775 
776   // Keep track of whether we are able to remove all the uses of the global
777   // other than the store that defines it.
778   bool AllNonStoreUsesGone = true;
779 
780   // Replace all uses of loads with uses of uses of the stored value.
781   for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
782     User *GlobalUser = *GUI++;
783     if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
784       Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
785       // If we were able to delete all uses of the loads
786       if (LI->use_empty()) {
787         LI->eraseFromParent();
788         Changed = true;
789       } else {
790         AllNonStoreUsesGone = false;
791       }
792     } else if (isa<StoreInst>(GlobalUser)) {
793       // Ignore the store that stores "LV" to the global.
794       assert(GlobalUser->getOperand(1) == GV &&
795              "Must be storing *to* the global");
796     } else {
797       AllNonStoreUsesGone = false;
798 
799       // If we get here we could have other crazy uses that are transitively
800       // loaded.
801       assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
802               isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser)) &&
803              "Only expect load and stores!");
804     }
805   }
806 
807   if (Changed) {
808     DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
809     ++NumGlobUses;
810   }
811 
812   // If we nuked all of the loads, then none of the stores are needed either,
813   // nor is the global.
814   if (AllNonStoreUsesGone) {
815     DEBUG(dbgs() << "  *** GLOBAL NOW DEAD!\n");
816     CleanupConstantGlobalUsers(GV, 0);
817     if (GV->use_empty()) {
818       GV->eraseFromParent();
819       ++NumDeleted;
820     }
821     Changed = true;
822   }
823   return Changed;
824 }
825 
826 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
827 /// instructions that are foldable.
ConstantPropUsersOf(Value * V)828 static void ConstantPropUsersOf(Value *V) {
829   for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
830     if (Instruction *I = dyn_cast<Instruction>(*UI++))
831       if (Constant *NewC = ConstantFoldInstruction(I)) {
832         I->replaceAllUsesWith(NewC);
833 
834         // Advance UI to the next non-I use to avoid invalidating it!
835         // Instructions could multiply use V.
836         while (UI != E && *UI == I)
837           ++UI;
838         I->eraseFromParent();
839       }
840 }
841 
842 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
843 /// variable, and transforms the program as if it always contained the result of
844 /// the specified malloc.  Because it is always the result of the specified
845 /// malloc, there is no reason to actually DO the malloc.  Instead, turn the
846 /// malloc into a global, and any loads of GV as uses of the new global.
OptimizeGlobalAddressOfMalloc(GlobalVariable * GV,CallInst * CI,Type * AllocTy,ConstantInt * NElements,TargetData * TD)847 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
848                                                      CallInst *CI,
849                                                      Type *AllocTy,
850                                                      ConstantInt *NElements,
851                                                      TargetData* TD) {
852   DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << "  CALL = " << *CI << '\n');
853 
854   Type *GlobalType;
855   if (NElements->getZExtValue() == 1)
856     GlobalType = AllocTy;
857   else
858     // If we have an array allocation, the global variable is of an array.
859     GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
860 
861   // Create the new global variable.  The contents of the malloc'd memory is
862   // undefined, so initialize with an undef value.
863   GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
864                                              GlobalType, false,
865                                              GlobalValue::InternalLinkage,
866                                              UndefValue::get(GlobalType),
867                                              GV->getName()+".body",
868                                              GV,
869                                              GV->isThreadLocal());
870 
871   // If there are bitcast users of the malloc (which is typical, usually we have
872   // a malloc + bitcast) then replace them with uses of the new global.  Update
873   // other users to use the global as well.
874   BitCastInst *TheBC = 0;
875   while (!CI->use_empty()) {
876     Instruction *User = cast<Instruction>(CI->use_back());
877     if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
878       if (BCI->getType() == NewGV->getType()) {
879         BCI->replaceAllUsesWith(NewGV);
880         BCI->eraseFromParent();
881       } else {
882         BCI->setOperand(0, NewGV);
883       }
884     } else {
885       if (TheBC == 0)
886         TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
887       User->replaceUsesOfWith(CI, TheBC);
888     }
889   }
890 
891   Constant *RepValue = NewGV;
892   if (NewGV->getType() != GV->getType()->getElementType())
893     RepValue = ConstantExpr::getBitCast(RepValue,
894                                         GV->getType()->getElementType());
895 
896   // If there is a comparison against null, we will insert a global bool to
897   // keep track of whether the global was initialized yet or not.
898   GlobalVariable *InitBool =
899     new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
900                        GlobalValue::InternalLinkage,
901                        ConstantInt::getFalse(GV->getContext()),
902                        GV->getName()+".init", GV->isThreadLocal());
903   bool InitBoolUsed = false;
904 
905   // Loop over all uses of GV, processing them in turn.
906   while (!GV->use_empty()) {
907     if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
908       // The global is initialized when the store to it occurs.
909       new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI);
910       SI->eraseFromParent();
911       continue;
912     }
913 
914     LoadInst *LI = cast<LoadInst>(GV->use_back());
915     while (!LI->use_empty()) {
916       Use &LoadUse = LI->use_begin().getUse();
917       if (!isa<ICmpInst>(LoadUse.getUser())) {
918         LoadUse = RepValue;
919         continue;
920       }
921 
922       ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
923       // Replace the cmp X, 0 with a use of the bool value.
924       Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI);
925       InitBoolUsed = true;
926       switch (ICI->getPredicate()) {
927       default: llvm_unreachable("Unknown ICmp Predicate!");
928       case ICmpInst::ICMP_ULT:
929       case ICmpInst::ICMP_SLT:   // X < null -> always false
930         LV = ConstantInt::getFalse(GV->getContext());
931         break;
932       case ICmpInst::ICMP_ULE:
933       case ICmpInst::ICMP_SLE:
934       case ICmpInst::ICMP_EQ:
935         LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
936         break;
937       case ICmpInst::ICMP_NE:
938       case ICmpInst::ICMP_UGE:
939       case ICmpInst::ICMP_SGE:
940       case ICmpInst::ICMP_UGT:
941       case ICmpInst::ICMP_SGT:
942         break;  // no change.
943       }
944       ICI->replaceAllUsesWith(LV);
945       ICI->eraseFromParent();
946     }
947     LI->eraseFromParent();
948   }
949 
950   // If the initialization boolean was used, insert it, otherwise delete it.
951   if (!InitBoolUsed) {
952     while (!InitBool->use_empty())  // Delete initializations
953       cast<StoreInst>(InitBool->use_back())->eraseFromParent();
954     delete InitBool;
955   } else
956     GV->getParent()->getGlobalList().insert(GV, InitBool);
957 
958   // Now the GV is dead, nuke it and the malloc..
959   GV->eraseFromParent();
960   CI->eraseFromParent();
961 
962   // To further other optimizations, loop over all users of NewGV and try to
963   // constant prop them.  This will promote GEP instructions with constant
964   // indices into GEP constant-exprs, which will allow global-opt to hack on it.
965   ConstantPropUsersOf(NewGV);
966   if (RepValue != NewGV)
967     ConstantPropUsersOf(RepValue);
968 
969   return NewGV;
970 }
971 
972 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
973 /// to make sure that there are no complex uses of V.  We permit simple things
974 /// like dereferencing the pointer, but not storing through the address, unless
975 /// it is to the specified global.
ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction * V,const GlobalVariable * GV,SmallPtrSet<const PHINode *,8> & PHIs)976 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
977                                                       const GlobalVariable *GV,
978                                          SmallPtrSet<const PHINode*, 8> &PHIs) {
979   for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
980        UI != E; ++UI) {
981     const Instruction *Inst = cast<Instruction>(*UI);
982 
983     if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
984       continue; // Fine, ignore.
985     }
986 
987     if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
988       if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
989         return false;  // Storing the pointer itself... bad.
990       continue; // Otherwise, storing through it, or storing into GV... fine.
991     }
992 
993     // Must index into the array and into the struct.
994     if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
995       if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
996         return false;
997       continue;
998     }
999 
1000     if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
1001       // PHIs are ok if all uses are ok.  Don't infinitely recurse through PHI
1002       // cycles.
1003       if (PHIs.insert(PN))
1004         if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
1005           return false;
1006       continue;
1007     }
1008 
1009     if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
1010       if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1011         return false;
1012       continue;
1013     }
1014 
1015     return false;
1016   }
1017   return true;
1018 }
1019 
1020 /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
1021 /// somewhere.  Transform all uses of the allocation into loads from the
1022 /// global and uses of the resultant pointer.  Further, delete the store into
1023 /// GV.  This assumes that these value pass the
1024 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
ReplaceUsesOfMallocWithGlobal(Instruction * Alloc,GlobalVariable * GV)1025 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1026                                           GlobalVariable *GV) {
1027   while (!Alloc->use_empty()) {
1028     Instruction *U = cast<Instruction>(*Alloc->use_begin());
1029     Instruction *InsertPt = U;
1030     if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1031       // If this is the store of the allocation into the global, remove it.
1032       if (SI->getOperand(1) == GV) {
1033         SI->eraseFromParent();
1034         continue;
1035       }
1036     } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1037       // Insert the load in the corresponding predecessor, not right before the
1038       // PHI.
1039       InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator();
1040     } else if (isa<BitCastInst>(U)) {
1041       // Must be bitcast between the malloc and store to initialize the global.
1042       ReplaceUsesOfMallocWithGlobal(U, GV);
1043       U->eraseFromParent();
1044       continue;
1045     } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1046       // If this is a "GEP bitcast" and the user is a store to the global, then
1047       // just process it as a bitcast.
1048       if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1049         if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back()))
1050           if (SI->getOperand(1) == GV) {
1051             // Must be bitcast GEP between the malloc and store to initialize
1052             // the global.
1053             ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1054             GEPI->eraseFromParent();
1055             continue;
1056           }
1057     }
1058 
1059     // Insert a load from the global, and use it instead of the malloc.
1060     Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1061     U->replaceUsesOfWith(Alloc, NL);
1062   }
1063 }
1064 
1065 /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
1066 /// of a load) are simple enough to perform heap SRA on.  This permits GEP's
1067 /// that index through the array and struct field, icmps of null, and PHIs.
LoadUsesSimpleEnoughForHeapSRA(const Value * V,SmallPtrSet<const PHINode *,32> & LoadUsingPHIs,SmallPtrSet<const PHINode *,32> & LoadUsingPHIsPerLoad)1068 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1069                         SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
1070                         SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) {
1071   // We permit two users of the load: setcc comparing against the null
1072   // pointer, and a getelementptr of a specific form.
1073   for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
1074        ++UI) {
1075     const Instruction *User = cast<Instruction>(*UI);
1076 
1077     // Comparison against null is ok.
1078     if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
1079       if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1080         return false;
1081       continue;
1082     }
1083 
1084     // getelementptr is also ok, but only a simple form.
1085     if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1086       // Must index into the array and into the struct.
1087       if (GEPI->getNumOperands() < 3)
1088         return false;
1089 
1090       // Otherwise the GEP is ok.
1091       continue;
1092     }
1093 
1094     if (const PHINode *PN = dyn_cast<PHINode>(User)) {
1095       if (!LoadUsingPHIsPerLoad.insert(PN))
1096         // This means some phi nodes are dependent on each other.
1097         // Avoid infinite looping!
1098         return false;
1099       if (!LoadUsingPHIs.insert(PN))
1100         // If we have already analyzed this PHI, then it is safe.
1101         continue;
1102 
1103       // Make sure all uses of the PHI are simple enough to transform.
1104       if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1105                                           LoadUsingPHIs, LoadUsingPHIsPerLoad))
1106         return false;
1107 
1108       continue;
1109     }
1110 
1111     // Otherwise we don't know what this is, not ok.
1112     return false;
1113   }
1114 
1115   return true;
1116 }
1117 
1118 
1119 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
1120 /// GV are simple enough to perform HeapSRA, return true.
AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable * GV,Instruction * StoredVal)1121 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1122                                                     Instruction *StoredVal) {
1123   SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1124   SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1125   for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1126        UI != E; ++UI)
1127     if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1128       if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1129                                           LoadUsingPHIsPerLoad))
1130         return false;
1131       LoadUsingPHIsPerLoad.clear();
1132     }
1133 
1134   // If we reach here, we know that all uses of the loads and transitive uses
1135   // (through PHI nodes) are simple enough to transform.  However, we don't know
1136   // that all inputs the to the PHI nodes are in the same equivalence sets.
1137   // Check to verify that all operands of the PHIs are either PHIS that can be
1138   // transformed, loads from GV, or MI itself.
1139   for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
1140        , E = LoadUsingPHIs.end(); I != E; ++I) {
1141     const PHINode *PN = *I;
1142     for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1143       Value *InVal = PN->getIncomingValue(op);
1144 
1145       // PHI of the stored value itself is ok.
1146       if (InVal == StoredVal) continue;
1147 
1148       if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1149         // One of the PHIs in our set is (optimistically) ok.
1150         if (LoadUsingPHIs.count(InPN))
1151           continue;
1152         return false;
1153       }
1154 
1155       // Load from GV is ok.
1156       if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1157         if (LI->getOperand(0) == GV)
1158           continue;
1159 
1160       // UNDEF? NULL?
1161 
1162       // Anything else is rejected.
1163       return false;
1164     }
1165   }
1166 
1167   return true;
1168 }
1169 
GetHeapSROAValue(Value * V,unsigned FieldNo,DenseMap<Value *,std::vector<Value * >> & InsertedScalarizedValues,std::vector<std::pair<PHINode *,unsigned>> & PHIsToRewrite)1170 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1171                DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1172                    std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1173   std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1174 
1175   if (FieldNo >= FieldVals.size())
1176     FieldVals.resize(FieldNo+1);
1177 
1178   // If we already have this value, just reuse the previously scalarized
1179   // version.
1180   if (Value *FieldVal = FieldVals[FieldNo])
1181     return FieldVal;
1182 
1183   // Depending on what instruction this is, we have several cases.
1184   Value *Result;
1185   if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1186     // This is a scalarized version of the load from the global.  Just create
1187     // a new Load of the scalarized global.
1188     Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1189                                            InsertedScalarizedValues,
1190                                            PHIsToRewrite),
1191                           LI->getName()+".f"+Twine(FieldNo), LI);
1192   } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
1193     // PN's type is pointer to struct.  Make a new PHI of pointer to struct
1194     // field.
1195     StructType *ST =
1196       cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
1197 
1198     PHINode *NewPN =
1199      PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
1200                      PN->getNumIncomingValues(),
1201                      PN->getName()+".f"+Twine(FieldNo), PN);
1202     Result = NewPN;
1203     PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1204   } else {
1205     llvm_unreachable("Unknown usable value");
1206     Result = 0;
1207   }
1208 
1209   return FieldVals[FieldNo] = Result;
1210 }
1211 
1212 /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
1213 /// the load, rewrite the derived value to use the HeapSRoA'd load.
RewriteHeapSROALoadUser(Instruction * LoadUser,DenseMap<Value *,std::vector<Value * >> & InsertedScalarizedValues,std::vector<std::pair<PHINode *,unsigned>> & PHIsToRewrite)1214 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1215              DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1216                    std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1217   // If this is a comparison against null, handle it.
1218   if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1219     assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1220     // If we have a setcc of the loaded pointer, we can use a setcc of any
1221     // field.
1222     Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1223                                    InsertedScalarizedValues, PHIsToRewrite);
1224 
1225     Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1226                               Constant::getNullValue(NPtr->getType()),
1227                               SCI->getName());
1228     SCI->replaceAllUsesWith(New);
1229     SCI->eraseFromParent();
1230     return;
1231   }
1232 
1233   // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1234   if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1235     assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1236            && "Unexpected GEPI!");
1237 
1238     // Load the pointer for this field.
1239     unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1240     Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1241                                      InsertedScalarizedValues, PHIsToRewrite);
1242 
1243     // Create the new GEP idx vector.
1244     SmallVector<Value*, 8> GEPIdx;
1245     GEPIdx.push_back(GEPI->getOperand(1));
1246     GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1247 
1248     Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
1249                                              GEPI->getName(), GEPI);
1250     GEPI->replaceAllUsesWith(NGEPI);
1251     GEPI->eraseFromParent();
1252     return;
1253   }
1254 
1255   // Recursively transform the users of PHI nodes.  This will lazily create the
1256   // PHIs that are needed for individual elements.  Keep track of what PHIs we
1257   // see in InsertedScalarizedValues so that we don't get infinite loops (very
1258   // antisocial).  If the PHI is already in InsertedScalarizedValues, it has
1259   // already been seen first by another load, so its uses have already been
1260   // processed.
1261   PHINode *PN = cast<PHINode>(LoadUser);
1262   if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1263                                               std::vector<Value*>())).second)
1264     return;
1265 
1266   // If this is the first time we've seen this PHI, recursively process all
1267   // users.
1268   for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
1269     Instruction *User = cast<Instruction>(*UI++);
1270     RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1271   }
1272 }
1273 
1274 /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global.  Ptr
1275 /// is a value loaded from the global.  Eliminate all uses of Ptr, making them
1276 /// use FieldGlobals instead.  All uses of loaded values satisfy
1277 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
RewriteUsesOfLoadForHeapSRoA(LoadInst * Load,DenseMap<Value *,std::vector<Value * >> & InsertedScalarizedValues,std::vector<std::pair<PHINode *,unsigned>> & PHIsToRewrite)1278 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1279                DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1280                    std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1281   for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
1282        UI != E; ) {
1283     Instruction *User = cast<Instruction>(*UI++);
1284     RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1285   }
1286 
1287   if (Load->use_empty()) {
1288     Load->eraseFromParent();
1289     InsertedScalarizedValues.erase(Load);
1290   }
1291 }
1292 
1293 /// PerformHeapAllocSRoA - CI is an allocation of an array of structures.  Break
1294 /// it up into multiple allocations of arrays of the fields.
PerformHeapAllocSRoA(GlobalVariable * GV,CallInst * CI,Value * NElems,TargetData * TD)1295 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1296                                             Value* NElems, TargetData *TD) {
1297   DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << "  MALLOC = " << *CI << '\n');
1298   Type* MAT = getMallocAllocatedType(CI);
1299   StructType *STy = cast<StructType>(MAT);
1300 
1301   // There is guaranteed to be at least one use of the malloc (storing
1302   // it into GV).  If there are other uses, change them to be uses of
1303   // the global to simplify later code.  This also deletes the store
1304   // into GV.
1305   ReplaceUsesOfMallocWithGlobal(CI, GV);
1306 
1307   // Okay, at this point, there are no users of the malloc.  Insert N
1308   // new mallocs at the same place as CI, and N globals.
1309   std::vector<Value*> FieldGlobals;
1310   std::vector<Value*> FieldMallocs;
1311 
1312   for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1313     Type *FieldTy = STy->getElementType(FieldNo);
1314     PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
1315 
1316     GlobalVariable *NGV =
1317       new GlobalVariable(*GV->getParent(),
1318                          PFieldTy, false, GlobalValue::InternalLinkage,
1319                          Constant::getNullValue(PFieldTy),
1320                          GV->getName() + ".f" + Twine(FieldNo), GV,
1321                          GV->isThreadLocal());
1322     FieldGlobals.push_back(NGV);
1323 
1324     unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
1325     if (StructType *ST = dyn_cast<StructType>(FieldTy))
1326       TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
1327     Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1328     Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1329                                         ConstantInt::get(IntPtrTy, TypeSize),
1330                                         NElems, 0,
1331                                         CI->getName() + ".f" + Twine(FieldNo));
1332     FieldMallocs.push_back(NMI);
1333     new StoreInst(NMI, NGV, CI);
1334   }
1335 
1336   // The tricky aspect of this transformation is handling the case when malloc
1337   // fails.  In the original code, malloc failing would set the result pointer
1338   // of malloc to null.  In this case, some mallocs could succeed and others
1339   // could fail.  As such, we emit code that looks like this:
1340   //    F0 = malloc(field0)
1341   //    F1 = malloc(field1)
1342   //    F2 = malloc(field2)
1343   //    if (F0 == 0 || F1 == 0 || F2 == 0) {
1344   //      if (F0) { free(F0); F0 = 0; }
1345   //      if (F1) { free(F1); F1 = 0; }
1346   //      if (F2) { free(F2); F2 = 0; }
1347   //    }
1348   // The malloc can also fail if its argument is too large.
1349   Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1350   Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1351                                   ConstantZero, "isneg");
1352   for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1353     Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1354                              Constant::getNullValue(FieldMallocs[i]->getType()),
1355                                "isnull");
1356     RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1357   }
1358 
1359   // Split the basic block at the old malloc.
1360   BasicBlock *OrigBB = CI->getParent();
1361   BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
1362 
1363   // Create the block to check the first condition.  Put all these blocks at the
1364   // end of the function as they are unlikely to be executed.
1365   BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1366                                                 "malloc_ret_null",
1367                                                 OrigBB->getParent());
1368 
1369   // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1370   // branch on RunningOr.
1371   OrigBB->getTerminator()->eraseFromParent();
1372   BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1373 
1374   // Within the NullPtrBlock, we need to emit a comparison and branch for each
1375   // pointer, because some may be null while others are not.
1376   for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1377     Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1378     Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1379                               Constant::getNullValue(GVVal->getType()));
1380     BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1381                                                OrigBB->getParent());
1382     BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1383                                                OrigBB->getParent());
1384     Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1385                                          Cmp, NullPtrBlock);
1386 
1387     // Fill in FreeBlock.
1388     CallInst::CreateFree(GVVal, BI);
1389     new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1390                   FreeBlock);
1391     BranchInst::Create(NextBlock, FreeBlock);
1392 
1393     NullPtrBlock = NextBlock;
1394   }
1395 
1396   BranchInst::Create(ContBB, NullPtrBlock);
1397 
1398   // CI is no longer needed, remove it.
1399   CI->eraseFromParent();
1400 
1401   /// InsertedScalarizedLoads - As we process loads, if we can't immediately
1402   /// update all uses of the load, keep track of what scalarized loads are
1403   /// inserted for a given load.
1404   DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1405   InsertedScalarizedValues[GV] = FieldGlobals;
1406 
1407   std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1408 
1409   // Okay, the malloc site is completely handled.  All of the uses of GV are now
1410   // loads, and all uses of those loads are simple.  Rewrite them to use loads
1411   // of the per-field globals instead.
1412   for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
1413     Instruction *User = cast<Instruction>(*UI++);
1414 
1415     if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1416       RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1417       continue;
1418     }
1419 
1420     // Must be a store of null.
1421     StoreInst *SI = cast<StoreInst>(User);
1422     assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1423            "Unexpected heap-sra user!");
1424 
1425     // Insert a store of null into each global.
1426     for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1427       PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1428       Constant *Null = Constant::getNullValue(PT->getElementType());
1429       new StoreInst(Null, FieldGlobals[i], SI);
1430     }
1431     // Erase the original store.
1432     SI->eraseFromParent();
1433   }
1434 
1435   // While we have PHIs that are interesting to rewrite, do it.
1436   while (!PHIsToRewrite.empty()) {
1437     PHINode *PN = PHIsToRewrite.back().first;
1438     unsigned FieldNo = PHIsToRewrite.back().second;
1439     PHIsToRewrite.pop_back();
1440     PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1441     assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1442 
1443     // Add all the incoming values.  This can materialize more phis.
1444     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1445       Value *InVal = PN->getIncomingValue(i);
1446       InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1447                                PHIsToRewrite);
1448       FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1449     }
1450   }
1451 
1452   // Drop all inter-phi links and any loads that made it this far.
1453   for (DenseMap<Value*, std::vector<Value*> >::iterator
1454        I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1455        I != E; ++I) {
1456     if (PHINode *PN = dyn_cast<PHINode>(I->first))
1457       PN->dropAllReferences();
1458     else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1459       LI->dropAllReferences();
1460   }
1461 
1462   // Delete all the phis and loads now that inter-references are dead.
1463   for (DenseMap<Value*, std::vector<Value*> >::iterator
1464        I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1465        I != E; ++I) {
1466     if (PHINode *PN = dyn_cast<PHINode>(I->first))
1467       PN->eraseFromParent();
1468     else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1469       LI->eraseFromParent();
1470   }
1471 
1472   // The old global is now dead, remove it.
1473   GV->eraseFromParent();
1474 
1475   ++NumHeapSRA;
1476   return cast<GlobalVariable>(FieldGlobals[0]);
1477 }
1478 
1479 /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
1480 /// pointer global variable with a single value stored it that is a malloc or
1481 /// cast of malloc.
TryToOptimizeStoreOfMallocToGlobal(GlobalVariable * GV,CallInst * CI,Type * AllocTy,Module::global_iterator & GVI,TargetData * TD)1482 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
1483                                                CallInst *CI,
1484                                                Type *AllocTy,
1485                                                Module::global_iterator &GVI,
1486                                                TargetData *TD) {
1487   if (!TD)
1488     return false;
1489 
1490   // If this is a malloc of an abstract type, don't touch it.
1491   if (!AllocTy->isSized())
1492     return false;
1493 
1494   // We can't optimize this global unless all uses of it are *known* to be
1495   // of the malloc value, not of the null initializer value (consider a use
1496   // that compares the global's value against zero to see if the malloc has
1497   // been reached).  To do this, we check to see if all uses of the global
1498   // would trap if the global were null: this proves that they must all
1499   // happen after the malloc.
1500   if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1501     return false;
1502 
1503   // We can't optimize this if the malloc itself is used in a complex way,
1504   // for example, being stored into multiple globals.  This allows the
1505   // malloc to be stored into the specified global, loaded setcc'd, and
1506   // GEP'd.  These are all things we could transform to using the global
1507   // for.
1508   SmallPtrSet<const PHINode*, 8> PHIs;
1509   if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1510     return false;
1511 
1512   // If we have a global that is only initialized with a fixed size malloc,
1513   // transform the program to use global memory instead of malloc'd memory.
1514   // This eliminates dynamic allocation, avoids an indirection accessing the
1515   // data, and exposes the resultant global to further GlobalOpt.
1516   // We cannot optimize the malloc if we cannot determine malloc array size.
1517   Value *NElems = getMallocArraySize(CI, TD, true);
1518   if (!NElems)
1519     return false;
1520 
1521   if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1522     // Restrict this transformation to only working on small allocations
1523     // (2048 bytes currently), as we don't want to introduce a 16M global or
1524     // something.
1525     if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
1526       GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD);
1527       return true;
1528     }
1529 
1530   // If the allocation is an array of structures, consider transforming this
1531   // into multiple malloc'd arrays, one for each field.  This is basically
1532   // SRoA for malloc'd memory.
1533 
1534   // If this is an allocation of a fixed size array of structs, analyze as a
1535   // variable size array.  malloc [100 x struct],1 -> malloc struct, 100
1536   if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1537     if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1538       AllocTy = AT->getElementType();
1539 
1540   StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1541   if (!AllocSTy)
1542     return false;
1543 
1544   // This the structure has an unreasonable number of fields, leave it
1545   // alone.
1546   if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1547       AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1548 
1549     // If this is a fixed size array, transform the Malloc to be an alloc of
1550     // structs.  malloc [100 x struct],1 -> malloc struct, 100
1551     if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI))) {
1552       Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1553       unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
1554       Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1555       Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1556       Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1557                                                    AllocSize, NumElements,
1558                                                    0, CI->getName());
1559       Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1560       CI->replaceAllUsesWith(Cast);
1561       CI->eraseFromParent();
1562       CI = dyn_cast<BitCastInst>(Malloc) ?
1563         extractMallocCallFromBitCast(Malloc) : cast<CallInst>(Malloc);
1564     }
1565 
1566     GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true),TD);
1567     return true;
1568   }
1569 
1570   return false;
1571 }
1572 
1573 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1574 // that only one value (besides its initializer) is ever stored to the global.
OptimizeOnceStoredGlobal(GlobalVariable * GV,Value * StoredOnceVal,Module::global_iterator & GVI,TargetData * TD)1575 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1576                                      Module::global_iterator &GVI,
1577                                      TargetData *TD) {
1578   // Ignore no-op GEPs and bitcasts.
1579   StoredOnceVal = StoredOnceVal->stripPointerCasts();
1580 
1581   // If we are dealing with a pointer global that is initialized to null and
1582   // only has one (non-null) value stored into it, then we can optimize any
1583   // users of the loaded value (often calls and loads) that would trap if the
1584   // value was null.
1585   if (GV->getInitializer()->getType()->isPointerTy() &&
1586       GV->getInitializer()->isNullValue()) {
1587     if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1588       if (GV->getInitializer()->getType() != SOVC->getType())
1589         SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1590 
1591       // Optimize away any trapping uses of the loaded value.
1592       if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
1593         return true;
1594     } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) {
1595       Type* MallocType = getMallocAllocatedType(CI);
1596       if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
1597                                                            GVI, TD))
1598         return true;
1599     }
1600   }
1601 
1602   return false;
1603 }
1604 
1605 /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
1606 /// two values ever stored into GV are its initializer and OtherVal.  See if we
1607 /// can shrink the global into a boolean and select between the two values
1608 /// whenever it is used.  This exposes the values to other scalar optimizations.
TryToShrinkGlobalToBoolean(GlobalVariable * GV,Constant * OtherVal)1609 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1610   Type *GVElType = GV->getType()->getElementType();
1611 
1612   // If GVElType is already i1, it is already shrunk.  If the type of the GV is
1613   // an FP value, pointer or vector, don't do this optimization because a select
1614   // between them is very expensive and unlikely to lead to later
1615   // simplification.  In these cases, we typically end up with "cond ? v1 : v2"
1616   // where v1 and v2 both require constant pool loads, a big loss.
1617   if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1618       GVElType->isFloatingPointTy() ||
1619       GVElType->isPointerTy() || GVElType->isVectorTy())
1620     return false;
1621 
1622   // Walk the use list of the global seeing if all the uses are load or store.
1623   // If there is anything else, bail out.
1624   for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
1625     User *U = *I;
1626     if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1627       return false;
1628   }
1629 
1630   DEBUG(dbgs() << "   *** SHRINKING TO BOOL: " << *GV);
1631 
1632   // Create the new global, initializing it to false.
1633   GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1634                                              false,
1635                                              GlobalValue::InternalLinkage,
1636                                         ConstantInt::getFalse(GV->getContext()),
1637                                              GV->getName()+".b",
1638                                              GV->isThreadLocal());
1639   GV->getParent()->getGlobalList().insert(GV, NewGV);
1640 
1641   Constant *InitVal = GV->getInitializer();
1642   assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1643          "No reason to shrink to bool!");
1644 
1645   // If initialized to zero and storing one into the global, we can use a cast
1646   // instead of a select to synthesize the desired value.
1647   bool IsOneZero = false;
1648   if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1649     IsOneZero = InitVal->isNullValue() && CI->isOne();
1650 
1651   while (!GV->use_empty()) {
1652     Instruction *UI = cast<Instruction>(GV->use_back());
1653     if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1654       // Change the store into a boolean store.
1655       bool StoringOther = SI->getOperand(0) == OtherVal;
1656       // Only do this if we weren't storing a loaded value.
1657       Value *StoreVal;
1658       if (StoringOther || SI->getOperand(0) == InitVal)
1659         StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1660                                     StoringOther);
1661       else {
1662         // Otherwise, we are storing a previously loaded copy.  To do this,
1663         // change the copy from copying the original value to just copying the
1664         // bool.
1665         Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1666 
1667         // If we've already replaced the input, StoredVal will be a cast or
1668         // select instruction.  If not, it will be a load of the original
1669         // global.
1670         if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1671           assert(LI->getOperand(0) == GV && "Not a copy!");
1672           // Insert a new load, to preserve the saved value.
1673           StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI);
1674         } else {
1675           assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1676                  "This is not a form that we understand!");
1677           StoreVal = StoredVal->getOperand(0);
1678           assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1679         }
1680       }
1681       new StoreInst(StoreVal, NewGV, SI);
1682     } else {
1683       // Change the load into a load of bool then a select.
1684       LoadInst *LI = cast<LoadInst>(UI);
1685       LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI);
1686       Value *NSI;
1687       if (IsOneZero)
1688         NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1689       else
1690         NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1691       NSI->takeName(LI);
1692       LI->replaceAllUsesWith(NSI);
1693     }
1694     UI->eraseFromParent();
1695   }
1696 
1697   GV->eraseFromParent();
1698   return true;
1699 }
1700 
1701 
1702 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1703 /// it if possible.  If we make a change, return true.
ProcessGlobal(GlobalVariable * GV,Module::global_iterator & GVI)1704 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1705                               Module::global_iterator &GVI) {
1706   if (!GV->hasLocalLinkage())
1707     return false;
1708 
1709   // Do more involved optimizations if the global is internal.
1710   GV->removeDeadConstantUsers();
1711 
1712   if (GV->use_empty()) {
1713     DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
1714     GV->eraseFromParent();
1715     ++NumDeleted;
1716     return true;
1717   }
1718 
1719   SmallPtrSet<const PHINode*, 16> PHIUsers;
1720   GlobalStatus GS;
1721 
1722   if (AnalyzeGlobal(GV, GS, PHIUsers))
1723     return false;
1724 
1725   if (!GS.isCompared && !GV->hasUnnamedAddr()) {
1726     GV->setUnnamedAddr(true);
1727     NumUnnamed++;
1728   }
1729 
1730   if (GV->isConstant() || !GV->hasInitializer())
1731     return false;
1732 
1733   return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
1734 }
1735 
1736 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1737 /// it if possible.  If we make a change, return true.
ProcessInternalGlobal(GlobalVariable * GV,Module::global_iterator & GVI,const SmallPtrSet<const PHINode *,16> & PHIUsers,const GlobalStatus & GS)1738 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1739                                       Module::global_iterator &GVI,
1740                                       const SmallPtrSet<const PHINode*, 16> &PHIUsers,
1741                                       const GlobalStatus &GS) {
1742   // If this is a first class global and has only one accessing function
1743   // and this function is main (which we know is not recursive we can make
1744   // this global a local variable) we replace the global with a local alloca
1745   // in this function.
1746   //
1747   // NOTE: It doesn't make sense to promote non single-value types since we
1748   // are just replacing static memory to stack memory.
1749   //
1750   // If the global is in different address space, don't bring it to stack.
1751   if (!GS.HasMultipleAccessingFunctions &&
1752       GS.AccessingFunction && !GS.HasNonInstructionUser &&
1753       GV->getType()->getElementType()->isSingleValueType() &&
1754       GS.AccessingFunction->getName() == "main" &&
1755       GS.AccessingFunction->hasExternalLinkage() &&
1756       GV->getType()->getAddressSpace() == 0) {
1757     DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
1758     Instruction& FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1759                                                    ->getEntryBlock().begin());
1760     Type* ElemTy = GV->getType()->getElementType();
1761     // FIXME: Pass Global's alignment when globals have alignment
1762     AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
1763     if (!isa<UndefValue>(GV->getInitializer()))
1764       new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1765 
1766     GV->replaceAllUsesWith(Alloca);
1767     GV->eraseFromParent();
1768     ++NumLocalized;
1769     return true;
1770   }
1771 
1772   // If the global is never loaded (but may be stored to), it is dead.
1773   // Delete it now.
1774   if (!GS.isLoaded) {
1775     DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
1776 
1777     // Delete any stores we can find to the global.  We may not be able to
1778     // make it completely dead though.
1779     bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer());
1780 
1781     // If the global is dead now, delete it.
1782     if (GV->use_empty()) {
1783       GV->eraseFromParent();
1784       ++NumDeleted;
1785       Changed = true;
1786     }
1787     return Changed;
1788 
1789   } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
1790     DEBUG(dbgs() << "MARKING CONSTANT: " << *GV);
1791     GV->setConstant(true);
1792 
1793     // Clean up any obviously simplifiable users now.
1794     CleanupConstantGlobalUsers(GV, GV->getInitializer());
1795 
1796     // If the global is dead now, just nuke it.
1797     if (GV->use_empty()) {
1798       DEBUG(dbgs() << "   *** Marking constant allowed us to simplify "
1799             << "all users and delete global!\n");
1800       GV->eraseFromParent();
1801       ++NumDeleted;
1802     }
1803 
1804     ++NumMarked;
1805     return true;
1806   } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
1807     if (TargetData *TD = getAnalysisIfAvailable<TargetData>())
1808       if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
1809         GVI = FirstNewGV;  // Don't skip the newly produced globals!
1810         return true;
1811       }
1812   } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
1813     // If the initial value for the global was an undef value, and if only
1814     // one other value was stored into it, we can just change the
1815     // initializer to be the stored value, then delete all stores to the
1816     // global.  This allows us to mark it constant.
1817     if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1818       if (isa<UndefValue>(GV->getInitializer())) {
1819         // Change the initial value here.
1820         GV->setInitializer(SOVConstant);
1821 
1822         // Clean up any obviously simplifiable users now.
1823         CleanupConstantGlobalUsers(GV, GV->getInitializer());
1824 
1825         if (GV->use_empty()) {
1826           DEBUG(dbgs() << "   *** Substituting initializer allowed us to "
1827                 << "simplify all users and delete global!\n");
1828           GV->eraseFromParent();
1829           ++NumDeleted;
1830         } else {
1831           GVI = GV;
1832         }
1833         ++NumSubstitute;
1834         return true;
1835       }
1836 
1837     // Try to optimize globals based on the knowledge that only one value
1838     // (besides its initializer) is ever stored to the global.
1839     if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
1840                                  getAnalysisIfAvailable<TargetData>()))
1841       return true;
1842 
1843     // Otherwise, if the global was not a boolean, we can shrink it to be a
1844     // boolean.
1845     if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1846       if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
1847         ++NumShrunkToBool;
1848         return true;
1849       }
1850   }
1851 
1852   return false;
1853 }
1854 
1855 /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
1856 /// function, changing them to FastCC.
ChangeCalleesToFastCall(Function * F)1857 static void ChangeCalleesToFastCall(Function *F) {
1858   for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1859     CallSite User(cast<Instruction>(*UI));
1860     User.setCallingConv(CallingConv::Fast);
1861   }
1862 }
1863 
StripNest(const AttrListPtr & Attrs)1864 static AttrListPtr StripNest(const AttrListPtr &Attrs) {
1865   for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
1866     if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0)
1867       continue;
1868 
1869     // There can be only one.
1870     return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest);
1871   }
1872 
1873   return Attrs;
1874 }
1875 
RemoveNestAttribute(Function * F)1876 static void RemoveNestAttribute(Function *F) {
1877   F->setAttributes(StripNest(F->getAttributes()));
1878   for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1879     CallSite User(cast<Instruction>(*UI));
1880     User.setAttributes(StripNest(User.getAttributes()));
1881   }
1882 }
1883 
OptimizeFunctions(Module & M)1884 bool GlobalOpt::OptimizeFunctions(Module &M) {
1885   bool Changed = false;
1886   // Optimize functions.
1887   for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
1888     Function *F = FI++;
1889     // Functions without names cannot be referenced outside this module.
1890     if (!F->hasName() && !F->isDeclaration())
1891       F->setLinkage(GlobalValue::InternalLinkage);
1892     F->removeDeadConstantUsers();
1893     if (F->use_empty() && (F->hasLocalLinkage() || F->hasLinkOnceLinkage())) {
1894       F->eraseFromParent();
1895       Changed = true;
1896       ++NumFnDeleted;
1897     } else if (F->hasLocalLinkage()) {
1898       if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
1899           !F->hasAddressTaken()) {
1900         // If this function has C calling conventions, is not a varargs
1901         // function, and is only called directly, promote it to use the Fast
1902         // calling convention.
1903         F->setCallingConv(CallingConv::Fast);
1904         ChangeCalleesToFastCall(F);
1905         ++NumFastCallFns;
1906         Changed = true;
1907       }
1908 
1909       if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
1910           !F->hasAddressTaken()) {
1911         // The function is not used by a trampoline intrinsic, so it is safe
1912         // to remove the 'nest' attribute.
1913         RemoveNestAttribute(F);
1914         ++NumNestRemoved;
1915         Changed = true;
1916       }
1917     }
1918   }
1919   return Changed;
1920 }
1921 
OptimizeGlobalVars(Module & M)1922 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
1923   bool Changed = false;
1924   for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
1925        GVI != E; ) {
1926     GlobalVariable *GV = GVI++;
1927     // Global variables without names cannot be referenced outside this module.
1928     if (!GV->hasName() && !GV->isDeclaration())
1929       GV->setLinkage(GlobalValue::InternalLinkage);
1930     // Simplify the initializer.
1931     if (GV->hasInitializer())
1932       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
1933         TargetData *TD = getAnalysisIfAvailable<TargetData>();
1934         Constant *New = ConstantFoldConstantExpression(CE, TD);
1935         if (New && New != CE)
1936           GV->setInitializer(New);
1937       }
1938 
1939     Changed |= ProcessGlobal(GV, GVI);
1940   }
1941   return Changed;
1942 }
1943 
1944 /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
1945 /// initializers have an init priority of 65535.
FindGlobalCtors(Module & M)1946 GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
1947   GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
1948   if (GV == 0) return 0;
1949 
1950   // Verify that the initializer is simple enough for us to handle. We are
1951   // only allowed to optimize the initializer if it is unique.
1952   if (!GV->hasUniqueInitializer()) return 0;
1953 
1954   if (isa<ConstantAggregateZero>(GV->getInitializer()))
1955     return GV;
1956   ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1957 
1958   for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
1959     if (isa<ConstantAggregateZero>(*i))
1960       continue;
1961     ConstantStruct *CS = cast<ConstantStruct>(*i);
1962     if (isa<ConstantPointerNull>(CS->getOperand(1)))
1963       continue;
1964 
1965     // Must have a function or null ptr.
1966     if (!isa<Function>(CS->getOperand(1)))
1967       return 0;
1968 
1969     // Init priority must be standard.
1970     ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
1971     if (CI->getZExtValue() != 65535)
1972       return 0;
1973   }
1974 
1975   return GV;
1976 }
1977 
1978 /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
1979 /// return a list of the functions and null terminator as a vector.
ParseGlobalCtors(GlobalVariable * GV)1980 static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
1981   if (GV->getInitializer()->isNullValue())
1982     return std::vector<Function*>();
1983   ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1984   std::vector<Function*> Result;
1985   Result.reserve(CA->getNumOperands());
1986   for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
1987     ConstantStruct *CS = cast<ConstantStruct>(*i);
1988     Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
1989   }
1990   return Result;
1991 }
1992 
1993 /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
1994 /// specified array, returning the new global to use.
InstallGlobalCtors(GlobalVariable * GCL,const std::vector<Function * > & Ctors)1995 static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
1996                                           const std::vector<Function*> &Ctors) {
1997   // If we made a change, reassemble the initializer list.
1998   Constant *CSVals[2];
1999   CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
2000   CSVals[1] = 0;
2001 
2002   StructType *StructTy =
2003     cast <StructType>(
2004     cast<ArrayType>(GCL->getType()->getElementType())->getElementType());
2005 
2006   // Create the new init list.
2007   std::vector<Constant*> CAList;
2008   for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
2009     if (Ctors[i]) {
2010       CSVals[1] = Ctors[i];
2011     } else {
2012       Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
2013                                           false);
2014       PointerType *PFTy = PointerType::getUnqual(FTy);
2015       CSVals[1] = Constant::getNullValue(PFTy);
2016       CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
2017                                    0x7fffffff);
2018     }
2019     CAList.push_back(ConstantStruct::get(StructTy, CSVals));
2020   }
2021 
2022   // Create the array initializer.
2023   Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
2024                                                    CAList.size()), CAList);
2025 
2026   // If we didn't change the number of elements, don't create a new GV.
2027   if (CA->getType() == GCL->getInitializer()->getType()) {
2028     GCL->setInitializer(CA);
2029     return GCL;
2030   }
2031 
2032   // Create the new global and insert it next to the existing list.
2033   GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
2034                                            GCL->getLinkage(), CA, "",
2035                                            GCL->isThreadLocal());
2036   GCL->getParent()->getGlobalList().insert(GCL, NGV);
2037   NGV->takeName(GCL);
2038 
2039   // Nuke the old list, replacing any uses with the new one.
2040   if (!GCL->use_empty()) {
2041     Constant *V = NGV;
2042     if (V->getType() != GCL->getType())
2043       V = ConstantExpr::getBitCast(V, GCL->getType());
2044     GCL->replaceAllUsesWith(V);
2045   }
2046   GCL->eraseFromParent();
2047 
2048   if (Ctors.size())
2049     return NGV;
2050   else
2051     return 0;
2052 }
2053 
2054 
getVal(DenseMap<Value *,Constant * > & ComputedValues,Value * V)2055 static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, Value *V) {
2056   if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2057   Constant *R = ComputedValues[V];
2058   assert(R && "Reference to an uncomputed value!");
2059   return R;
2060 }
2061 
2062 static inline bool
2063 isSimpleEnoughValueToCommit(Constant *C,
2064                             SmallPtrSet<Constant*, 8> &SimpleConstants);
2065 
2066 
2067 /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
2068 /// handled by the code generator.  We don't want to generate something like:
2069 ///   void *X = &X/42;
2070 /// because the code generator doesn't have a relocation that can handle that.
2071 ///
2072 /// This function should be called if C was not found (but just got inserted)
2073 /// in SimpleConstants to avoid having to rescan the same constants all the
2074 /// time.
isSimpleEnoughValueToCommitHelper(Constant * C,SmallPtrSet<Constant *,8> & SimpleConstants)2075 static bool isSimpleEnoughValueToCommitHelper(Constant *C,
2076                                    SmallPtrSet<Constant*, 8> &SimpleConstants) {
2077   // Simple integer, undef, constant aggregate zero, global addresses, etc are
2078   // all supported.
2079   if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
2080       isa<GlobalValue>(C))
2081     return true;
2082 
2083   // Aggregate values are safe if all their elements are.
2084   if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2085       isa<ConstantVector>(C)) {
2086     for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
2087       Constant *Op = cast<Constant>(C->getOperand(i));
2088       if (!isSimpleEnoughValueToCommit(Op, SimpleConstants))
2089         return false;
2090     }
2091     return true;
2092   }
2093 
2094   // We don't know exactly what relocations are allowed in constant expressions,
2095   // so we allow &global+constantoffset, which is safe and uniformly supported
2096   // across targets.
2097   ConstantExpr *CE = cast<ConstantExpr>(C);
2098   switch (CE->getOpcode()) {
2099   case Instruction::BitCast:
2100   case Instruction::IntToPtr:
2101   case Instruction::PtrToInt:
2102     // These casts are always fine if the casted value is.
2103     return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
2104 
2105   // GEP is fine if it is simple + constant offset.
2106   case Instruction::GetElementPtr:
2107     for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2108       if (!isa<ConstantInt>(CE->getOperand(i)))
2109         return false;
2110     return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
2111 
2112   case Instruction::Add:
2113     // We allow simple+cst.
2114     if (!isa<ConstantInt>(CE->getOperand(1)))
2115       return false;
2116     return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
2117   }
2118   return false;
2119 }
2120 
2121 static inline bool
isSimpleEnoughValueToCommit(Constant * C,SmallPtrSet<Constant *,8> & SimpleConstants)2122 isSimpleEnoughValueToCommit(Constant *C,
2123                             SmallPtrSet<Constant*, 8> &SimpleConstants) {
2124   // If we already checked this constant, we win.
2125   if (!SimpleConstants.insert(C)) return true;
2126   // Check the constant.
2127   return isSimpleEnoughValueToCommitHelper(C, SimpleConstants);
2128 }
2129 
2130 
2131 /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
2132 /// enough for us to understand.  In particular, if it is a cast to anything
2133 /// other than from one pointer type to another pointer type, we punt.
2134 /// We basically just support direct accesses to globals and GEP's of
2135 /// globals.  This should be kept up to date with CommitValueTo.
isSimpleEnoughPointerToCommit(Constant * C)2136 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2137   // Conservatively, avoid aggregate types. This is because we don't
2138   // want to worry about them partially overlapping other stores.
2139   if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2140     return false;
2141 
2142   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2143     // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2144     // external globals.
2145     return GV->hasUniqueInitializer();
2146 
2147   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2148     // Handle a constantexpr gep.
2149     if (CE->getOpcode() == Instruction::GetElementPtr &&
2150         isa<GlobalVariable>(CE->getOperand(0)) &&
2151         cast<GEPOperator>(CE)->isInBounds()) {
2152       GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2153       // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2154       // external globals.
2155       if (!GV->hasUniqueInitializer())
2156         return false;
2157 
2158       // The first index must be zero.
2159       ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
2160       if (!CI || !CI->isZero()) return false;
2161 
2162       // The remaining indices must be compile-time known integers within the
2163       // notional bounds of the corresponding static array types.
2164       if (!CE->isGEPWithNoNotionalOverIndexing())
2165         return false;
2166 
2167       return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2168 
2169     // A constantexpr bitcast from a pointer to another pointer is a no-op,
2170     // and we know how to evaluate it by moving the bitcast from the pointer
2171     // operand to the value operand.
2172     } else if (CE->getOpcode() == Instruction::BitCast &&
2173                isa<GlobalVariable>(CE->getOperand(0))) {
2174       // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2175       // external globals.
2176       return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2177     }
2178   }
2179 
2180   return false;
2181 }
2182 
2183 /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
2184 /// initializer.  This returns 'Init' modified to reflect 'Val' stored into it.
2185 /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
EvaluateStoreInto(Constant * Init,Constant * Val,ConstantExpr * Addr,unsigned OpNo)2186 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2187                                    ConstantExpr *Addr, unsigned OpNo) {
2188   // Base case of the recursion.
2189   if (OpNo == Addr->getNumOperands()) {
2190     assert(Val->getType() == Init->getType() && "Type mismatch!");
2191     return Val;
2192   }
2193 
2194   std::vector<Constant*> Elts;
2195   if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2196 
2197     // Break up the constant into its elements.
2198     if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
2199       for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i)
2200         Elts.push_back(cast<Constant>(*i));
2201     } else if (isa<ConstantAggregateZero>(Init)) {
2202       for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2203         Elts.push_back(Constant::getNullValue(STy->getElementType(i)));
2204     } else if (isa<UndefValue>(Init)) {
2205       for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2206         Elts.push_back(UndefValue::get(STy->getElementType(i)));
2207     } else {
2208       llvm_unreachable("This code is out of sync with "
2209              " ConstantFoldLoadThroughGEPConstantExpr");
2210     }
2211 
2212     // Replace the element that we are supposed to.
2213     ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2214     unsigned Idx = CU->getZExtValue();
2215     assert(Idx < STy->getNumElements() && "Struct index out of range!");
2216     Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2217 
2218     // Return the modified struct.
2219     return ConstantStruct::get(STy, Elts);
2220   }
2221 
2222   ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2223   SequentialType *InitTy = cast<SequentialType>(Init->getType());
2224 
2225   uint64_t NumElts;
2226   if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2227     NumElts = ATy->getNumElements();
2228   else
2229     NumElts = cast<VectorType>(InitTy)->getNumElements();
2230 
2231   // Break up the array into elements.
2232   if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
2233     for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i)
2234       Elts.push_back(cast<Constant>(*i));
2235   } else if (ConstantVector *CV = dyn_cast<ConstantVector>(Init)) {
2236     for (User::op_iterator i = CV->op_begin(), e = CV->op_end(); i != e; ++i)
2237       Elts.push_back(cast<Constant>(*i));
2238   } else if (isa<ConstantAggregateZero>(Init)) {
2239     Elts.assign(NumElts, Constant::getNullValue(InitTy->getElementType()));
2240   } else {
2241     assert(isa<UndefValue>(Init) && "This code is out of sync with "
2242            " ConstantFoldLoadThroughGEPConstantExpr");
2243     Elts.assign(NumElts, UndefValue::get(InitTy->getElementType()));
2244   }
2245 
2246   assert(CI->getZExtValue() < NumElts);
2247   Elts[CI->getZExtValue()] =
2248     EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2249 
2250   if (Init->getType()->isArrayTy())
2251     return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2252   return ConstantVector::get(Elts);
2253 }
2254 
2255 /// CommitValueTo - We have decided that Addr (which satisfies the predicate
2256 /// isSimpleEnoughPointerToCommit) should get Val as its value.  Make it happen.
CommitValueTo(Constant * Val,Constant * Addr)2257 static void CommitValueTo(Constant *Val, Constant *Addr) {
2258   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2259     assert(GV->hasInitializer());
2260     GV->setInitializer(Val);
2261     return;
2262   }
2263 
2264   ConstantExpr *CE = cast<ConstantExpr>(Addr);
2265   GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2266   GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2267 }
2268 
2269 /// ComputeLoadResult - Return the value that would be computed by a load from
2270 /// P after the stores reflected by 'memory' have been performed.  If we can't
2271 /// decide, return null.
ComputeLoadResult(Constant * P,const DenseMap<Constant *,Constant * > & Memory)2272 static Constant *ComputeLoadResult(Constant *P,
2273                                 const DenseMap<Constant*, Constant*> &Memory) {
2274   // If this memory location has been recently stored, use the stored value: it
2275   // is the most up-to-date.
2276   DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P);
2277   if (I != Memory.end()) return I->second;
2278 
2279   // Access it.
2280   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2281     if (GV->hasDefinitiveInitializer())
2282       return GV->getInitializer();
2283     return 0;
2284   }
2285 
2286   // Handle a constantexpr getelementptr.
2287   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2288     if (CE->getOpcode() == Instruction::GetElementPtr &&
2289         isa<GlobalVariable>(CE->getOperand(0))) {
2290       GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2291       if (GV->hasDefinitiveInitializer())
2292         return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2293     }
2294 
2295   return 0;  // don't know how to evaluate.
2296 }
2297 
2298 /// EvaluateFunction - Evaluate a call to function F, returning true if
2299 /// successful, false if we can't evaluate it.  ActualArgs contains the formal
2300 /// arguments for the function.
EvaluateFunction(Function * F,Constant * & RetVal,const SmallVectorImpl<Constant * > & ActualArgs,std::vector<Function * > & CallStack,DenseMap<Constant *,Constant * > & MutatedMemory,std::vector<GlobalVariable * > & AllocaTmps,SmallPtrSet<Constant *,8> & SimpleConstants,const TargetData * TD)2301 static bool EvaluateFunction(Function *F, Constant *&RetVal,
2302                              const SmallVectorImpl<Constant*> &ActualArgs,
2303                              std::vector<Function*> &CallStack,
2304                              DenseMap<Constant*, Constant*> &MutatedMemory,
2305                              std::vector<GlobalVariable*> &AllocaTmps,
2306                              SmallPtrSet<Constant*, 8> &SimpleConstants,
2307                              const TargetData *TD) {
2308   // Check to see if this function is already executing (recursion).  If so,
2309   // bail out.  TODO: we might want to accept limited recursion.
2310   if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2311     return false;
2312 
2313   CallStack.push_back(F);
2314 
2315   /// Values - As we compute SSA register values, we store their contents here.
2316   DenseMap<Value*, Constant*> Values;
2317 
2318   // Initialize arguments to the incoming values specified.
2319   unsigned ArgNo = 0;
2320   for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2321        ++AI, ++ArgNo)
2322     Values[AI] = ActualArgs[ArgNo];
2323 
2324   /// ExecutedBlocks - We only handle non-looping, non-recursive code.  As such,
2325   /// we can only evaluate any one basic block at most once.  This set keeps
2326   /// track of what we have executed so we can detect recursive cases etc.
2327   SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2328 
2329   // CurInst - The current instruction we're evaluating.
2330   BasicBlock::iterator CurInst = F->begin()->begin();
2331 
2332   // This is the main evaluation loop.
2333   while (1) {
2334     Constant *InstResult = 0;
2335 
2336     if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2337       if (!SI->isSimple()) return false;  // no volatile/atomic accesses.
2338       Constant *Ptr = getVal(Values, SI->getOperand(1));
2339       if (!isSimpleEnoughPointerToCommit(Ptr))
2340         // If this is too complex for us to commit, reject it.
2341         return false;
2342 
2343       Constant *Val = getVal(Values, SI->getOperand(0));
2344 
2345       // If this might be too difficult for the backend to handle (e.g. the addr
2346       // of one global variable divided by another) then we can't commit it.
2347       if (!isSimpleEnoughValueToCommit(Val, SimpleConstants))
2348         return false;
2349 
2350       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2351         if (CE->getOpcode() == Instruction::BitCast) {
2352           // If we're evaluating a store through a bitcast, then we need
2353           // to pull the bitcast off the pointer type and push it onto the
2354           // stored value.
2355           Ptr = CE->getOperand(0);
2356 
2357           Type *NewTy=cast<PointerType>(Ptr->getType())->getElementType();
2358 
2359           // In order to push the bitcast onto the stored value, a bitcast
2360           // from NewTy to Val's type must be legal.  If it's not, we can try
2361           // introspecting NewTy to find a legal conversion.
2362           while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2363             // If NewTy is a struct, we can convert the pointer to the struct
2364             // into a pointer to its first member.
2365             // FIXME: This could be extended to support arrays as well.
2366             if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2367               NewTy = STy->getTypeAtIndex(0U);
2368 
2369               IntegerType *IdxTy =IntegerType::get(NewTy->getContext(), 32);
2370               Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2371               Constant * const IdxList[] = {IdxZero, IdxZero};
2372 
2373               Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
2374 
2375             // If we can't improve the situation by introspecting NewTy,
2376             // we have to give up.
2377             } else {
2378               return 0;
2379             }
2380           }
2381 
2382           // If we found compatible types, go ahead and push the bitcast
2383           // onto the stored value.
2384           Val = ConstantExpr::getBitCast(Val, NewTy);
2385         }
2386 
2387       MutatedMemory[Ptr] = Val;
2388     } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2389       InstResult = ConstantExpr::get(BO->getOpcode(),
2390                                      getVal(Values, BO->getOperand(0)),
2391                                      getVal(Values, BO->getOperand(1)));
2392     } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2393       InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2394                                             getVal(Values, CI->getOperand(0)),
2395                                             getVal(Values, CI->getOperand(1)));
2396     } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2397       InstResult = ConstantExpr::getCast(CI->getOpcode(),
2398                                          getVal(Values, CI->getOperand(0)),
2399                                          CI->getType());
2400     } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2401       InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)),
2402                                            getVal(Values, SI->getOperand(1)),
2403                                            getVal(Values, SI->getOperand(2)));
2404     } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2405       Constant *P = getVal(Values, GEP->getOperand(0));
2406       SmallVector<Constant*, 8> GEPOps;
2407       for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2408            i != e; ++i)
2409         GEPOps.push_back(getVal(Values, *i));
2410       InstResult =
2411         ConstantExpr::getGetElementPtr(P, GEPOps,
2412                                        cast<GEPOperator>(GEP)->isInBounds());
2413     } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2414       if (!LI->isSimple()) return false;  // no volatile/atomic accesses.
2415       InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)),
2416                                      MutatedMemory);
2417       if (InstResult == 0) return false; // Could not evaluate load.
2418     } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2419       if (AI->isArrayAllocation()) return false;  // Cannot handle array allocs.
2420       Type *Ty = AI->getType()->getElementType();
2421       AllocaTmps.push_back(new GlobalVariable(Ty, false,
2422                                               GlobalValue::InternalLinkage,
2423                                               UndefValue::get(Ty),
2424                                               AI->getName()));
2425       InstResult = AllocaTmps.back();
2426     } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) {
2427 
2428       // Debug info can safely be ignored here.
2429       if (isa<DbgInfoIntrinsic>(CI)) {
2430         ++CurInst;
2431         continue;
2432       }
2433 
2434       // Cannot handle inline asm.
2435       if (isa<InlineAsm>(CI->getCalledValue())) return false;
2436 
2437       if (MemSetInst *MSI = dyn_cast<MemSetInst>(CI)) {
2438         if (MSI->isVolatile()) return false;
2439         Constant *Ptr = getVal(Values, MSI->getDest());
2440         Constant *Val = getVal(Values, MSI->getValue());
2441         Constant *DestVal = ComputeLoadResult(getVal(Values, Ptr),
2442                                               MutatedMemory);
2443         if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2444           // This memset is a no-op.
2445           ++CurInst;
2446           continue;
2447         }
2448         return false;
2449       }
2450 
2451       // Resolve function pointers.
2452       Function *Callee = dyn_cast<Function>(getVal(Values,
2453                                                    CI->getCalledValue()));
2454       if (!Callee) return false;  // Cannot resolve.
2455 
2456       SmallVector<Constant*, 8> Formals;
2457       CallSite CS(CI);
2458       for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end();
2459            i != e; ++i)
2460         Formals.push_back(getVal(Values, *i));
2461 
2462       if (Callee->isDeclaration()) {
2463         // If this is a function we can constant fold, do it.
2464         if (Constant *C = ConstantFoldCall(Callee, Formals)) {
2465           InstResult = C;
2466         } else {
2467           return false;
2468         }
2469       } else {
2470         if (Callee->getFunctionType()->isVarArg())
2471           return false;
2472 
2473         Constant *RetVal;
2474         // Execute the call, if successful, use the return value.
2475         if (!EvaluateFunction(Callee, RetVal, Formals, CallStack,
2476                               MutatedMemory, AllocaTmps, SimpleConstants, TD))
2477           return false;
2478         InstResult = RetVal;
2479       }
2480     } else if (isa<TerminatorInst>(CurInst)) {
2481       BasicBlock *NewBB = 0;
2482       if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2483         if (BI->isUnconditional()) {
2484           NewBB = BI->getSuccessor(0);
2485         } else {
2486           ConstantInt *Cond =
2487             dyn_cast<ConstantInt>(getVal(Values, BI->getCondition()));
2488           if (!Cond) return false;  // Cannot determine.
2489 
2490           NewBB = BI->getSuccessor(!Cond->getZExtValue());
2491         }
2492       } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2493         ConstantInt *Val =
2494           dyn_cast<ConstantInt>(getVal(Values, SI->getCondition()));
2495         if (!Val) return false;  // Cannot determine.
2496         NewBB = SI->getSuccessor(SI->findCaseValue(Val));
2497       } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2498         Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts();
2499         if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2500           NewBB = BA->getBasicBlock();
2501         else
2502           return false;  // Cannot determine.
2503       } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) {
2504         if (RI->getNumOperands())
2505           RetVal = getVal(Values, RI->getOperand(0));
2506 
2507         CallStack.pop_back();  // return from fn.
2508         return true;  // We succeeded at evaluating this ctor!
2509       } else {
2510         // invoke, unwind, resume, unreachable.
2511         return false;  // Cannot handle this terminator.
2512       }
2513 
2514       // Okay, we succeeded in evaluating this control flow.  See if we have
2515       // executed the new block before.  If so, we have a looping function,
2516       // which we cannot evaluate in reasonable time.
2517       if (!ExecutedBlocks.insert(NewBB))
2518         return false;  // looped!
2519 
2520       // Okay, we have never been in this block before.  Check to see if there
2521       // are any PHI nodes.  If so, evaluate them with information about where
2522       // we came from.
2523       BasicBlock *OldBB = CurInst->getParent();
2524       CurInst = NewBB->begin();
2525       PHINode *PN;
2526       for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2527         Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB));
2528 
2529       // Do NOT increment CurInst.  We know that the terminator had no value.
2530       continue;
2531     } else {
2532       // Did not know how to evaluate this!
2533       return false;
2534     }
2535 
2536     if (!CurInst->use_empty()) {
2537       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2538         InstResult = ConstantFoldConstantExpression(CE, TD);
2539 
2540       Values[CurInst] = InstResult;
2541     }
2542 
2543     // Advance program counter.
2544     ++CurInst;
2545   }
2546 }
2547 
2548 /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
2549 /// we can.  Return true if we can, false otherwise.
EvaluateStaticConstructor(Function * F,const TargetData * TD)2550 static bool EvaluateStaticConstructor(Function *F, const TargetData *TD) {
2551   /// MutatedMemory - For each store we execute, we update this map.  Loads
2552   /// check this to get the most up-to-date value.  If evaluation is successful,
2553   /// this state is committed to the process.
2554   DenseMap<Constant*, Constant*> MutatedMemory;
2555 
2556   /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
2557   /// to represent its body.  This vector is needed so we can delete the
2558   /// temporary globals when we are done.
2559   std::vector<GlobalVariable*> AllocaTmps;
2560 
2561   /// CallStack - This is used to detect recursion.  In pathological situations
2562   /// we could hit exponential behavior, but at least there is nothing
2563   /// unbounded.
2564   std::vector<Function*> CallStack;
2565 
2566   /// SimpleConstants - These are constants we have checked and know to be
2567   /// simple enough to live in a static initializer of a global.
2568   SmallPtrSet<Constant*, 8> SimpleConstants;
2569 
2570   // Call the function.
2571   Constant *RetValDummy;
2572   bool EvalSuccess = EvaluateFunction(F, RetValDummy,
2573                                       SmallVector<Constant*, 0>(), CallStack,
2574                                       MutatedMemory, AllocaTmps,
2575                                       SimpleConstants, TD);
2576 
2577   if (EvalSuccess) {
2578     // We succeeded at evaluation: commit the result.
2579     DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2580           << F->getName() << "' to " << MutatedMemory.size()
2581           << " stores.\n");
2582     for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
2583          E = MutatedMemory.end(); I != E; ++I)
2584       CommitValueTo(I->second, I->first);
2585   }
2586 
2587   // At this point, we are done interpreting.  If we created any 'alloca'
2588   // temporaries, release them now.
2589   while (!AllocaTmps.empty()) {
2590     GlobalVariable *Tmp = AllocaTmps.back();
2591     AllocaTmps.pop_back();
2592 
2593     // If there are still users of the alloca, the program is doing something
2594     // silly, e.g. storing the address of the alloca somewhere and using it
2595     // later.  Since this is undefined, we'll just make it be null.
2596     if (!Tmp->use_empty())
2597       Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2598     delete Tmp;
2599   }
2600 
2601   return EvalSuccess;
2602 }
2603 
2604 
2605 
2606 /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
2607 /// Return true if anything changed.
OptimizeGlobalCtorsList(GlobalVariable * & GCL)2608 bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
2609   std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
2610   bool MadeChange = false;
2611   if (Ctors.empty()) return false;
2612 
2613   const TargetData *TD = getAnalysisIfAvailable<TargetData>();
2614   // Loop over global ctors, optimizing them when we can.
2615   for (unsigned i = 0; i != Ctors.size(); ++i) {
2616     Function *F = Ctors[i];
2617     // Found a null terminator in the middle of the list, prune off the rest of
2618     // the list.
2619     if (F == 0) {
2620       if (i != Ctors.size()-1) {
2621         Ctors.resize(i+1);
2622         MadeChange = true;
2623       }
2624       break;
2625     }
2626 
2627     // We cannot simplify external ctor functions.
2628     if (F->empty()) continue;
2629 
2630     // If we can evaluate the ctor at compile time, do.
2631     if (EvaluateStaticConstructor(F, TD)) {
2632       Ctors.erase(Ctors.begin()+i);
2633       MadeChange = true;
2634       --i;
2635       ++NumCtorsEvaluated;
2636       continue;
2637     }
2638   }
2639 
2640   if (!MadeChange) return false;
2641 
2642   GCL = InstallGlobalCtors(GCL, Ctors);
2643   return true;
2644 }
2645 
OptimizeGlobalAliases(Module & M)2646 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2647   bool Changed = false;
2648 
2649   for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2650        I != E;) {
2651     Module::alias_iterator J = I++;
2652     // Aliases without names cannot be referenced outside this module.
2653     if (!J->hasName() && !J->isDeclaration())
2654       J->setLinkage(GlobalValue::InternalLinkage);
2655     // If the aliasee may change at link time, nothing can be done - bail out.
2656     if (J->mayBeOverridden())
2657       continue;
2658 
2659     Constant *Aliasee = J->getAliasee();
2660     GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2661     Target->removeDeadConstantUsers();
2662     bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
2663 
2664     // Make all users of the alias use the aliasee instead.
2665     if (!J->use_empty()) {
2666       J->replaceAllUsesWith(Aliasee);
2667       ++NumAliasesResolved;
2668       Changed = true;
2669     }
2670 
2671     // If the alias is externally visible, we may still be able to simplify it.
2672     if (!J->hasLocalLinkage()) {
2673       // If the aliasee has internal linkage, give it the name and linkage
2674       // of the alias, and delete the alias.  This turns:
2675       //   define internal ... @f(...)
2676       //   @a = alias ... @f
2677       // into:
2678       //   define ... @a(...)
2679       if (!Target->hasLocalLinkage())
2680         continue;
2681 
2682       // Do not perform the transform if multiple aliases potentially target the
2683       // aliasee. This check also ensures that it is safe to replace the section
2684       // and other attributes of the aliasee with those of the alias.
2685       if (!hasOneUse)
2686         continue;
2687 
2688       // Give the aliasee the name, linkage and other attributes of the alias.
2689       Target->takeName(J);
2690       Target->setLinkage(J->getLinkage());
2691       Target->GlobalValue::copyAttributesFrom(J);
2692     }
2693 
2694     // Delete the alias.
2695     M.getAliasList().erase(J);
2696     ++NumAliasesRemoved;
2697     Changed = true;
2698   }
2699 
2700   return Changed;
2701 }
2702 
FindCXAAtExit(Module & M)2703 static Function *FindCXAAtExit(Module &M) {
2704   Function *Fn = M.getFunction("__cxa_atexit");
2705 
2706   if (!Fn)
2707     return 0;
2708 
2709   FunctionType *FTy = Fn->getFunctionType();
2710 
2711   // Checking that the function has the right return type, the right number of
2712   // parameters and that they all have pointer types should be enough.
2713   if (!FTy->getReturnType()->isIntegerTy() ||
2714       FTy->getNumParams() != 3 ||
2715       !FTy->getParamType(0)->isPointerTy() ||
2716       !FTy->getParamType(1)->isPointerTy() ||
2717       !FTy->getParamType(2)->isPointerTy())
2718     return 0;
2719 
2720   return Fn;
2721 }
2722 
2723 /// cxxDtorIsEmpty - Returns whether the given function is an empty C++
2724 /// destructor and can therefore be eliminated.
2725 /// Note that we assume that other optimization passes have already simplified
2726 /// the code so we only look for a function with a single basic block, where
2727 /// the only allowed instructions are 'ret' or 'call' to empty C++ dtor.
cxxDtorIsEmpty(const Function & Fn,SmallPtrSet<const Function *,8> & CalledFunctions)2728 static bool cxxDtorIsEmpty(const Function &Fn,
2729                            SmallPtrSet<const Function *, 8> &CalledFunctions) {
2730   // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
2731   // nounwind, but that doesn't seem worth doing.
2732   if (Fn.isDeclaration())
2733     return false;
2734 
2735   if (++Fn.begin() != Fn.end())
2736     return false;
2737 
2738   const BasicBlock &EntryBlock = Fn.getEntryBlock();
2739   for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
2740        I != E; ++I) {
2741     if (const CallInst *CI = dyn_cast<CallInst>(I)) {
2742       // Ignore debug intrinsics.
2743       if (isa<DbgInfoIntrinsic>(CI))
2744         continue;
2745 
2746       const Function *CalledFn = CI->getCalledFunction();
2747 
2748       if (!CalledFn)
2749         return false;
2750 
2751       SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
2752 
2753       // Don't treat recursive functions as empty.
2754       if (!NewCalledFunctions.insert(CalledFn))
2755         return false;
2756 
2757       if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
2758         return false;
2759     } else if (isa<ReturnInst>(*I))
2760       return true;
2761     else
2762       return false;
2763   }
2764 
2765   return false;
2766 }
2767 
OptimizeEmptyGlobalCXXDtors(Function * CXAAtExitFn)2768 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
2769   /// Itanium C++ ABI p3.3.5:
2770   ///
2771   ///   After constructing a global (or local static) object, that will require
2772   ///   destruction on exit, a termination function is registered as follows:
2773   ///
2774   ///   extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
2775   ///
2776   ///   This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
2777   ///   call f(p) when DSO d is unloaded, before all such termination calls
2778   ///   registered before this one. It returns zero if registration is
2779   ///   successful, nonzero on failure.
2780 
2781   // This pass will look for calls to __cxa_atexit where the function is trivial
2782   // and remove them.
2783   bool Changed = false;
2784 
2785   for (Function::use_iterator I = CXAAtExitFn->use_begin(),
2786        E = CXAAtExitFn->use_end(); I != E;) {
2787     // We're only interested in calls. Theoretically, we could handle invoke
2788     // instructions as well, but neither llvm-gcc nor clang generate invokes
2789     // to __cxa_atexit.
2790     CallInst *CI = dyn_cast<CallInst>(*I++);
2791     if (!CI)
2792       continue;
2793 
2794     Function *DtorFn =
2795       dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
2796     if (!DtorFn)
2797       continue;
2798 
2799     SmallPtrSet<const Function *, 8> CalledFunctions;
2800     if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
2801       continue;
2802 
2803     // Just remove the call.
2804     CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
2805     CI->eraseFromParent();
2806 
2807     ++NumCXXDtorsRemoved;
2808 
2809     Changed |= true;
2810   }
2811 
2812   return Changed;
2813 }
2814 
runOnModule(Module & M)2815 bool GlobalOpt::runOnModule(Module &M) {
2816   bool Changed = false;
2817 
2818   // Try to find the llvm.globalctors list.
2819   GlobalVariable *GlobalCtors = FindGlobalCtors(M);
2820 
2821   Function *CXAAtExitFn = FindCXAAtExit(M);
2822 
2823   bool LocalChange = true;
2824   while (LocalChange) {
2825     LocalChange = false;
2826 
2827     // Delete functions that are trivially dead, ccc -> fastcc
2828     LocalChange |= OptimizeFunctions(M);
2829 
2830     // Optimize global_ctors list.
2831     if (GlobalCtors)
2832       LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
2833 
2834     // Optimize non-address-taken globals.
2835     LocalChange |= OptimizeGlobalVars(M);
2836 
2837     // Resolve aliases, when possible.
2838     LocalChange |= OptimizeGlobalAliases(M);
2839 
2840     // Try to remove trivial global destructors.
2841     if (CXAAtExitFn)
2842       LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
2843 
2844     Changed |= LocalChange;
2845   }
2846 
2847   // TODO: Move all global ctors functions to the end of the module for code
2848   // layout.
2849 
2850   return Changed;
2851 }
2852