1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
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 performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
12 //
13 // Note that this pass does the value numbering itself; it does not use the
14 // ValueNumbering analysis passes.
15 //
16 //===----------------------------------------------------------------------===//
17
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/GlobalVariable.h"
21 #include "llvm/IntrinsicInst.h"
22 #include "llvm/LLVMContext.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Analysis/ConstantFolding.h"
25 #include "llvm/Analysis/Dominators.h"
26 #include "llvm/Analysis/InstructionSimplify.h"
27 #include "llvm/Analysis/Loads.h"
28 #include "llvm/Analysis/MemoryBuiltins.h"
29 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
30 #include "llvm/Analysis/PHITransAddr.h"
31 #include "llvm/Analysis/ValueTracking.h"
32 #include "llvm/Assembly/Writer.h"
33 #include "llvm/Target/TargetData.h"
34 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
35 #include "llvm/Transforms/Utils/SSAUpdater.h"
36 #include "llvm/ADT/DenseMap.h"
37 #include "llvm/ADT/DepthFirstIterator.h"
38 #include "llvm/ADT/SmallPtrSet.h"
39 #include "llvm/ADT/Statistic.h"
40 #include "llvm/Support/Allocator.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Support/IRBuilder.h"
44 #include "llvm/Support/PatternMatch.h"
45 using namespace llvm;
46 using namespace PatternMatch;
47
48 STATISTIC(NumGVNInstr, "Number of instructions deleted");
49 STATISTIC(NumGVNLoad, "Number of loads deleted");
50 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
51 STATISTIC(NumGVNBlocks, "Number of blocks merged");
52 STATISTIC(NumGVNSimpl, "Number of instructions simplified");
53 STATISTIC(NumGVNEqProp, "Number of equalities propagated");
54 STATISTIC(NumPRELoad, "Number of loads PRE'd");
55
56 static cl::opt<bool> EnablePRE("enable-pre",
57 cl::init(true), cl::Hidden);
58 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
59
60 //===----------------------------------------------------------------------===//
61 // ValueTable Class
62 //===----------------------------------------------------------------------===//
63
64 /// This class holds the mapping between values and value numbers. It is used
65 /// as an efficient mechanism to determine the expression-wise equivalence of
66 /// two values.
67 namespace {
68 struct Expression {
69 uint32_t opcode;
70 Type *type;
71 SmallVector<uint32_t, 4> varargs;
72
Expression__anond0db39690111::Expression73 Expression(uint32_t o = ~2U) : opcode(o) { }
74
operator ==__anond0db39690111::Expression75 bool operator==(const Expression &other) const {
76 if (opcode != other.opcode)
77 return false;
78 if (opcode == ~0U || opcode == ~1U)
79 return true;
80 if (type != other.type)
81 return false;
82 if (varargs != other.varargs)
83 return false;
84 return true;
85 }
86 };
87
88 class ValueTable {
89 DenseMap<Value*, uint32_t> valueNumbering;
90 DenseMap<Expression, uint32_t> expressionNumbering;
91 AliasAnalysis *AA;
92 MemoryDependenceAnalysis *MD;
93 DominatorTree *DT;
94
95 uint32_t nextValueNumber;
96
97 Expression create_expression(Instruction* I);
98 Expression create_extractvalue_expression(ExtractValueInst* EI);
99 uint32_t lookup_or_add_call(CallInst* C);
100 public:
ValueTable()101 ValueTable() : nextValueNumber(1) { }
102 uint32_t lookup_or_add(Value *V);
103 uint32_t lookup(Value *V) const;
104 void add(Value *V, uint32_t num);
105 void clear();
106 void erase(Value *v);
setAliasAnalysis(AliasAnalysis * A)107 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
getAliasAnalysis() const108 AliasAnalysis *getAliasAnalysis() const { return AA; }
setMemDep(MemoryDependenceAnalysis * M)109 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
setDomTree(DominatorTree * D)110 void setDomTree(DominatorTree* D) { DT = D; }
getNextUnusedValueNumber()111 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
112 void verifyRemoved(const Value *) const;
113 };
114 }
115
116 namespace llvm {
117 template <> struct DenseMapInfo<Expression> {
getEmptyKeyllvm::DenseMapInfo118 static inline Expression getEmptyKey() {
119 return ~0U;
120 }
121
getTombstoneKeyllvm::DenseMapInfo122 static inline Expression getTombstoneKey() {
123 return ~1U;
124 }
125
getHashValuellvm::DenseMapInfo126 static unsigned getHashValue(const Expression e) {
127 unsigned hash = e.opcode;
128
129 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
130 (unsigned)((uintptr_t)e.type >> 9));
131
132 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
133 E = e.varargs.end(); I != E; ++I)
134 hash = *I + hash * 37;
135
136 return hash;
137 }
isEqualllvm::DenseMapInfo138 static bool isEqual(const Expression &LHS, const Expression &RHS) {
139 return LHS == RHS;
140 }
141 };
142
143 }
144
145 //===----------------------------------------------------------------------===//
146 // ValueTable Internal Functions
147 //===----------------------------------------------------------------------===//
148
create_expression(Instruction * I)149 Expression ValueTable::create_expression(Instruction *I) {
150 Expression e;
151 e.type = I->getType();
152 e.opcode = I->getOpcode();
153 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
154 OI != OE; ++OI)
155 e.varargs.push_back(lookup_or_add(*OI));
156
157 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
158 e.opcode = (C->getOpcode() << 8) | C->getPredicate();
159 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) {
160 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
161 II != IE; ++II)
162 e.varargs.push_back(*II);
163 }
164
165 return e;
166 }
167
create_extractvalue_expression(ExtractValueInst * EI)168 Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) {
169 assert(EI != 0 && "Not an ExtractValueInst?");
170 Expression e;
171 e.type = EI->getType();
172 e.opcode = 0;
173
174 IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
175 if (I != 0 && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) {
176 // EI might be an extract from one of our recognised intrinsics. If it
177 // is we'll synthesize a semantically equivalent expression instead on
178 // an extract value expression.
179 switch (I->getIntrinsicID()) {
180 case Intrinsic::sadd_with_overflow:
181 case Intrinsic::uadd_with_overflow:
182 e.opcode = Instruction::Add;
183 break;
184 case Intrinsic::ssub_with_overflow:
185 case Intrinsic::usub_with_overflow:
186 e.opcode = Instruction::Sub;
187 break;
188 case Intrinsic::smul_with_overflow:
189 case Intrinsic::umul_with_overflow:
190 e.opcode = Instruction::Mul;
191 break;
192 default:
193 break;
194 }
195
196 if (e.opcode != 0) {
197 // Intrinsic recognized. Grab its args to finish building the expression.
198 assert(I->getNumArgOperands() == 2 &&
199 "Expect two args for recognised intrinsics.");
200 e.varargs.push_back(lookup_or_add(I->getArgOperand(0)));
201 e.varargs.push_back(lookup_or_add(I->getArgOperand(1)));
202 return e;
203 }
204 }
205
206 // Not a recognised intrinsic. Fall back to producing an extract value
207 // expression.
208 e.opcode = EI->getOpcode();
209 for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end();
210 OI != OE; ++OI)
211 e.varargs.push_back(lookup_or_add(*OI));
212
213 for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end();
214 II != IE; ++II)
215 e.varargs.push_back(*II);
216
217 return e;
218 }
219
220 //===----------------------------------------------------------------------===//
221 // ValueTable External Functions
222 //===----------------------------------------------------------------------===//
223
224 /// add - Insert a value into the table with a specified value number.
add(Value * V,uint32_t num)225 void ValueTable::add(Value *V, uint32_t num) {
226 valueNumbering.insert(std::make_pair(V, num));
227 }
228
lookup_or_add_call(CallInst * C)229 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
230 if (AA->doesNotAccessMemory(C)) {
231 Expression exp = create_expression(C);
232 uint32_t& e = expressionNumbering[exp];
233 if (!e) e = nextValueNumber++;
234 valueNumbering[C] = e;
235 return e;
236 } else if (AA->onlyReadsMemory(C)) {
237 Expression exp = create_expression(C);
238 uint32_t& e = expressionNumbering[exp];
239 if (!e) {
240 e = nextValueNumber++;
241 valueNumbering[C] = e;
242 return e;
243 }
244 if (!MD) {
245 e = nextValueNumber++;
246 valueNumbering[C] = e;
247 return e;
248 }
249
250 MemDepResult local_dep = MD->getDependency(C);
251
252 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
253 valueNumbering[C] = nextValueNumber;
254 return nextValueNumber++;
255 }
256
257 if (local_dep.isDef()) {
258 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
259
260 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
261 valueNumbering[C] = nextValueNumber;
262 return nextValueNumber++;
263 }
264
265 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
266 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
267 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i));
268 if (c_vn != cd_vn) {
269 valueNumbering[C] = nextValueNumber;
270 return nextValueNumber++;
271 }
272 }
273
274 uint32_t v = lookup_or_add(local_cdep);
275 valueNumbering[C] = v;
276 return v;
277 }
278
279 // Non-local case.
280 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
281 MD->getNonLocalCallDependency(CallSite(C));
282 // FIXME: Move the checking logic to MemDep!
283 CallInst* cdep = 0;
284
285 // Check to see if we have a single dominating call instruction that is
286 // identical to C.
287 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
288 const NonLocalDepEntry *I = &deps[i];
289 if (I->getResult().isNonLocal())
290 continue;
291
292 // We don't handle non-definitions. If we already have a call, reject
293 // instruction dependencies.
294 if (!I->getResult().isDef() || cdep != 0) {
295 cdep = 0;
296 break;
297 }
298
299 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
300 // FIXME: All duplicated with non-local case.
301 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
302 cdep = NonLocalDepCall;
303 continue;
304 }
305
306 cdep = 0;
307 break;
308 }
309
310 if (!cdep) {
311 valueNumbering[C] = nextValueNumber;
312 return nextValueNumber++;
313 }
314
315 if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
316 valueNumbering[C] = nextValueNumber;
317 return nextValueNumber++;
318 }
319 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
320 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
321 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i));
322 if (c_vn != cd_vn) {
323 valueNumbering[C] = nextValueNumber;
324 return nextValueNumber++;
325 }
326 }
327
328 uint32_t v = lookup_or_add(cdep);
329 valueNumbering[C] = v;
330 return v;
331
332 } else {
333 valueNumbering[C] = nextValueNumber;
334 return nextValueNumber++;
335 }
336 }
337
338 /// lookup_or_add - Returns the value number for the specified value, assigning
339 /// it a new number if it did not have one before.
lookup_or_add(Value * V)340 uint32_t ValueTable::lookup_or_add(Value *V) {
341 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
342 if (VI != valueNumbering.end())
343 return VI->second;
344
345 if (!isa<Instruction>(V)) {
346 valueNumbering[V] = nextValueNumber;
347 return nextValueNumber++;
348 }
349
350 Instruction* I = cast<Instruction>(V);
351 Expression exp;
352 switch (I->getOpcode()) {
353 case Instruction::Call:
354 return lookup_or_add_call(cast<CallInst>(I));
355 case Instruction::Add:
356 case Instruction::FAdd:
357 case Instruction::Sub:
358 case Instruction::FSub:
359 case Instruction::Mul:
360 case Instruction::FMul:
361 case Instruction::UDiv:
362 case Instruction::SDiv:
363 case Instruction::FDiv:
364 case Instruction::URem:
365 case Instruction::SRem:
366 case Instruction::FRem:
367 case Instruction::Shl:
368 case Instruction::LShr:
369 case Instruction::AShr:
370 case Instruction::And:
371 case Instruction::Or :
372 case Instruction::Xor:
373 case Instruction::ICmp:
374 case Instruction::FCmp:
375 case Instruction::Trunc:
376 case Instruction::ZExt:
377 case Instruction::SExt:
378 case Instruction::FPToUI:
379 case Instruction::FPToSI:
380 case Instruction::UIToFP:
381 case Instruction::SIToFP:
382 case Instruction::FPTrunc:
383 case Instruction::FPExt:
384 case Instruction::PtrToInt:
385 case Instruction::IntToPtr:
386 case Instruction::BitCast:
387 case Instruction::Select:
388 case Instruction::ExtractElement:
389 case Instruction::InsertElement:
390 case Instruction::ShuffleVector:
391 case Instruction::InsertValue:
392 case Instruction::GetElementPtr:
393 exp = create_expression(I);
394 break;
395 case Instruction::ExtractValue:
396 exp = create_extractvalue_expression(cast<ExtractValueInst>(I));
397 break;
398 default:
399 valueNumbering[V] = nextValueNumber;
400 return nextValueNumber++;
401 }
402
403 uint32_t& e = expressionNumbering[exp];
404 if (!e) e = nextValueNumber++;
405 valueNumbering[V] = e;
406 return e;
407 }
408
409 /// lookup - Returns the value number of the specified value. Fails if
410 /// the value has not yet been numbered.
lookup(Value * V) const411 uint32_t ValueTable::lookup(Value *V) const {
412 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
413 assert(VI != valueNumbering.end() && "Value not numbered?");
414 return VI->second;
415 }
416
417 /// clear - Remove all entries from the ValueTable.
clear()418 void ValueTable::clear() {
419 valueNumbering.clear();
420 expressionNumbering.clear();
421 nextValueNumber = 1;
422 }
423
424 /// erase - Remove a value from the value numbering.
erase(Value * V)425 void ValueTable::erase(Value *V) {
426 valueNumbering.erase(V);
427 }
428
429 /// verifyRemoved - Verify that the value is removed from all internal data
430 /// structures.
verifyRemoved(const Value * V) const431 void ValueTable::verifyRemoved(const Value *V) const {
432 for (DenseMap<Value*, uint32_t>::const_iterator
433 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
434 assert(I->first != V && "Inst still occurs in value numbering map!");
435 }
436 }
437
438 //===----------------------------------------------------------------------===//
439 // GVN Pass
440 //===----------------------------------------------------------------------===//
441
442 namespace {
443
444 class GVN : public FunctionPass {
445 bool NoLoads;
446 MemoryDependenceAnalysis *MD;
447 DominatorTree *DT;
448 const TargetData *TD;
449
450 ValueTable VN;
451
452 /// LeaderTable - A mapping from value numbers to lists of Value*'s that
453 /// have that value number. Use findLeader to query it.
454 struct LeaderTableEntry {
455 Value *Val;
456 BasicBlock *BB;
457 LeaderTableEntry *Next;
458 };
459 DenseMap<uint32_t, LeaderTableEntry> LeaderTable;
460 BumpPtrAllocator TableAllocator;
461
462 SmallVector<Instruction*, 8> InstrsToErase;
463 public:
464 static char ID; // Pass identification, replacement for typeid
GVN(bool noloads=false)465 explicit GVN(bool noloads = false)
466 : FunctionPass(ID), NoLoads(noloads), MD(0) {
467 initializeGVNPass(*PassRegistry::getPassRegistry());
468 }
469
470 bool runOnFunction(Function &F);
471
472 /// markInstructionForDeletion - This removes the specified instruction from
473 /// our various maps and marks it for deletion.
markInstructionForDeletion(Instruction * I)474 void markInstructionForDeletion(Instruction *I) {
475 VN.erase(I);
476 InstrsToErase.push_back(I);
477 }
478
getTargetData() const479 const TargetData *getTargetData() const { return TD; }
getDominatorTree() const480 DominatorTree &getDominatorTree() const { return *DT; }
getAliasAnalysis() const481 AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); }
getMemDep() const482 MemoryDependenceAnalysis &getMemDep() const { return *MD; }
483 private:
484 /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for
485 /// its value number.
addToLeaderTable(uint32_t N,Value * V,BasicBlock * BB)486 void addToLeaderTable(uint32_t N, Value *V, BasicBlock *BB) {
487 LeaderTableEntry &Curr = LeaderTable[N];
488 if (!Curr.Val) {
489 Curr.Val = V;
490 Curr.BB = BB;
491 return;
492 }
493
494 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>();
495 Node->Val = V;
496 Node->BB = BB;
497 Node->Next = Curr.Next;
498 Curr.Next = Node;
499 }
500
501 /// removeFromLeaderTable - Scan the list of values corresponding to a given
502 /// value number, and remove the given value if encountered.
removeFromLeaderTable(uint32_t N,Value * V,BasicBlock * BB)503 void removeFromLeaderTable(uint32_t N, Value *V, BasicBlock *BB) {
504 LeaderTableEntry* Prev = 0;
505 LeaderTableEntry* Curr = &LeaderTable[N];
506
507 while (Curr->Val != V || Curr->BB != BB) {
508 Prev = Curr;
509 Curr = Curr->Next;
510 }
511
512 if (Prev) {
513 Prev->Next = Curr->Next;
514 } else {
515 if (!Curr->Next) {
516 Curr->Val = 0;
517 Curr->BB = 0;
518 } else {
519 LeaderTableEntry* Next = Curr->Next;
520 Curr->Val = Next->Val;
521 Curr->BB = Next->BB;
522 Curr->Next = Next->Next;
523 }
524 }
525 }
526
527 // List of critical edges to be split between iterations.
528 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
529
530 // This transformation requires dominator postdominator info
getAnalysisUsage(AnalysisUsage & AU) const531 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
532 AU.addRequired<DominatorTree>();
533 if (!NoLoads)
534 AU.addRequired<MemoryDependenceAnalysis>();
535 AU.addRequired<AliasAnalysis>();
536
537 AU.addPreserved<DominatorTree>();
538 AU.addPreserved<AliasAnalysis>();
539 }
540
541
542 // Helper fuctions
543 // FIXME: eliminate or document these better
544 bool processLoad(LoadInst *L);
545 bool processInstruction(Instruction *I);
546 bool processNonLocalLoad(LoadInst *L);
547 bool processBlock(BasicBlock *BB);
548 void dump(DenseMap<uint32_t, Value*> &d);
549 bool iterateOnFunction(Function &F);
550 bool performPRE(Function &F);
551 Value *findLeader(BasicBlock *BB, uint32_t num);
552 void cleanupGlobalSets();
553 void verifyRemoved(const Instruction *I) const;
554 bool splitCriticalEdges();
555 unsigned replaceAllDominatedUsesWith(Value *From, Value *To,
556 BasicBlock *Root);
557 bool propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root);
558 };
559
560 char GVN::ID = 0;
561 }
562
563 // createGVNPass - The public interface to this file...
createGVNPass(bool NoLoads)564 FunctionPass *llvm::createGVNPass(bool NoLoads) {
565 return new GVN(NoLoads);
566 }
567
568 INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)569 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
570 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
571 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
572 INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false)
573
574 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
575 errs() << "{\n";
576 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
577 E = d.end(); I != E; ++I) {
578 errs() << I->first << "\n";
579 I->second->dump();
580 }
581 errs() << "}\n";
582 }
583
584 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
585 /// we're analyzing is fully available in the specified block. As we go, keep
586 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
587 /// map is actually a tri-state map with the following values:
588 /// 0) we know the block *is not* fully available.
589 /// 1) we know the block *is* fully available.
590 /// 2) we do not know whether the block is fully available or not, but we are
591 /// currently speculating that it will be.
592 /// 3) we are speculating for this block and have used that to speculate for
593 /// other blocks.
IsValueFullyAvailableInBlock(BasicBlock * BB,DenseMap<BasicBlock *,char> & FullyAvailableBlocks)594 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
595 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
596 // Optimistically assume that the block is fully available and check to see
597 // if we already know about this block in one lookup.
598 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
599 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
600
601 // If the entry already existed for this block, return the precomputed value.
602 if (!IV.second) {
603 // If this is a speculative "available" value, mark it as being used for
604 // speculation of other blocks.
605 if (IV.first->second == 2)
606 IV.first->second = 3;
607 return IV.first->second != 0;
608 }
609
610 // Otherwise, see if it is fully available in all predecessors.
611 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
612
613 // If this block has no predecessors, it isn't live-in here.
614 if (PI == PE)
615 goto SpeculationFailure;
616
617 for (; PI != PE; ++PI)
618 // If the value isn't fully available in one of our predecessors, then it
619 // isn't fully available in this block either. Undo our previous
620 // optimistic assumption and bail out.
621 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
622 goto SpeculationFailure;
623
624 return true;
625
626 // SpeculationFailure - If we get here, we found out that this is not, after
627 // all, a fully-available block. We have a problem if we speculated on this and
628 // used the speculation to mark other blocks as available.
629 SpeculationFailure:
630 char &BBVal = FullyAvailableBlocks[BB];
631
632 // If we didn't speculate on this, just return with it set to false.
633 if (BBVal == 2) {
634 BBVal = 0;
635 return false;
636 }
637
638 // If we did speculate on this value, we could have blocks set to 1 that are
639 // incorrect. Walk the (transitive) successors of this block and mark them as
640 // 0 if set to one.
641 SmallVector<BasicBlock*, 32> BBWorklist;
642 BBWorklist.push_back(BB);
643
644 do {
645 BasicBlock *Entry = BBWorklist.pop_back_val();
646 // Note that this sets blocks to 0 (unavailable) if they happen to not
647 // already be in FullyAvailableBlocks. This is safe.
648 char &EntryVal = FullyAvailableBlocks[Entry];
649 if (EntryVal == 0) continue; // Already unavailable.
650
651 // Mark as unavailable.
652 EntryVal = 0;
653
654 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
655 BBWorklist.push_back(*I);
656 } while (!BBWorklist.empty());
657
658 return false;
659 }
660
661
662 /// CanCoerceMustAliasedValueToLoad - Return true if
663 /// CoerceAvailableValueToLoadType will succeed.
CanCoerceMustAliasedValueToLoad(Value * StoredVal,Type * LoadTy,const TargetData & TD)664 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
665 Type *LoadTy,
666 const TargetData &TD) {
667 // If the loaded or stored value is an first class array or struct, don't try
668 // to transform them. We need to be able to bitcast to integer.
669 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
670 StoredVal->getType()->isStructTy() ||
671 StoredVal->getType()->isArrayTy())
672 return false;
673
674 // The store has to be at least as big as the load.
675 if (TD.getTypeSizeInBits(StoredVal->getType()) <
676 TD.getTypeSizeInBits(LoadTy))
677 return false;
678
679 return true;
680 }
681
682
683 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
684 /// then a load from a must-aliased pointer of a different type, try to coerce
685 /// the stored value. LoadedTy is the type of the load we want to replace and
686 /// InsertPt is the place to insert new instructions.
687 ///
688 /// If we can't do it, return null.
CoerceAvailableValueToLoadType(Value * StoredVal,Type * LoadedTy,Instruction * InsertPt,const TargetData & TD)689 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
690 Type *LoadedTy,
691 Instruction *InsertPt,
692 const TargetData &TD) {
693 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
694 return 0;
695
696 // If this is already the right type, just return it.
697 Type *StoredValTy = StoredVal->getType();
698
699 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy);
700 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
701
702 // If the store and reload are the same size, we can always reuse it.
703 if (StoreSize == LoadSize) {
704 // Pointer to Pointer -> use bitcast.
705 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy())
706 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
707
708 // Convert source pointers to integers, which can be bitcast.
709 if (StoredValTy->isPointerTy()) {
710 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
711 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
712 }
713
714 Type *TypeToCastTo = LoadedTy;
715 if (TypeToCastTo->isPointerTy())
716 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
717
718 if (StoredValTy != TypeToCastTo)
719 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
720
721 // Cast to pointer if the load needs a pointer type.
722 if (LoadedTy->isPointerTy())
723 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
724
725 return StoredVal;
726 }
727
728 // If the loaded value is smaller than the available value, then we can
729 // extract out a piece from it. If the available value is too small, then we
730 // can't do anything.
731 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
732
733 // Convert source pointers to integers, which can be manipulated.
734 if (StoredValTy->isPointerTy()) {
735 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
736 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
737 }
738
739 // Convert vectors and fp to integer, which can be manipulated.
740 if (!StoredValTy->isIntegerTy()) {
741 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
742 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
743 }
744
745 // If this is a big-endian system, we need to shift the value down to the low
746 // bits so that a truncate will work.
747 if (TD.isBigEndian()) {
748 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
749 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
750 }
751
752 // Truncate the integer to the right size now.
753 Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
754 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
755
756 if (LoadedTy == NewIntTy)
757 return StoredVal;
758
759 // If the result is a pointer, inttoptr.
760 if (LoadedTy->isPointerTy())
761 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
762
763 // Otherwise, bitcast.
764 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
765 }
766
767 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
768 /// memdep query of a load that ends up being a clobbering memory write (store,
769 /// memset, memcpy, memmove). This means that the write *may* provide bits used
770 /// by the load but we can't be sure because the pointers don't mustalias.
771 ///
772 /// Check this case to see if there is anything more we can do before we give
773 /// up. This returns -1 if we have to give up, or a byte number in the stored
774 /// value of the piece that feeds the load.
AnalyzeLoadFromClobberingWrite(Type * LoadTy,Value * LoadPtr,Value * WritePtr,uint64_t WriteSizeInBits,const TargetData & TD)775 static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr,
776 Value *WritePtr,
777 uint64_t WriteSizeInBits,
778 const TargetData &TD) {
779 // If the loaded or stored value is an first class array or struct, don't try
780 // to transform them. We need to be able to bitcast to integer.
781 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
782 return -1;
783
784 int64_t StoreOffset = 0, LoadOffset = 0;
785 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr, StoreOffset,TD);
786 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
787 if (StoreBase != LoadBase)
788 return -1;
789
790 // If the load and store are to the exact same address, they should have been
791 // a must alias. AA must have gotten confused.
792 // FIXME: Study to see if/when this happens. One case is forwarding a memset
793 // to a load from the base of the memset.
794 #if 0
795 if (LoadOffset == StoreOffset) {
796 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
797 << "Base = " << *StoreBase << "\n"
798 << "Store Ptr = " << *WritePtr << "\n"
799 << "Store Offs = " << StoreOffset << "\n"
800 << "Load Ptr = " << *LoadPtr << "\n";
801 abort();
802 }
803 #endif
804
805 // If the load and store don't overlap at all, the store doesn't provide
806 // anything to the load. In this case, they really don't alias at all, AA
807 // must have gotten confused.
808 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
809
810 if ((WriteSizeInBits & 7) | (LoadSize & 7))
811 return -1;
812 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
813 LoadSize >>= 3;
814
815
816 bool isAAFailure = false;
817 if (StoreOffset < LoadOffset)
818 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
819 else
820 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
821
822 if (isAAFailure) {
823 #if 0
824 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
825 << "Base = " << *StoreBase << "\n"
826 << "Store Ptr = " << *WritePtr << "\n"
827 << "Store Offs = " << StoreOffset << "\n"
828 << "Load Ptr = " << *LoadPtr << "\n";
829 abort();
830 #endif
831 return -1;
832 }
833
834 // If the Load isn't completely contained within the stored bits, we don't
835 // have all the bits to feed it. We could do something crazy in the future
836 // (issue a smaller load then merge the bits in) but this seems unlikely to be
837 // valuable.
838 if (StoreOffset > LoadOffset ||
839 StoreOffset+StoreSize < LoadOffset+LoadSize)
840 return -1;
841
842 // Okay, we can do this transformation. Return the number of bytes into the
843 // store that the load is.
844 return LoadOffset-StoreOffset;
845 }
846
847 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
848 /// memdep query of a load that ends up being a clobbering store.
AnalyzeLoadFromClobberingStore(Type * LoadTy,Value * LoadPtr,StoreInst * DepSI,const TargetData & TD)849 static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr,
850 StoreInst *DepSI,
851 const TargetData &TD) {
852 // Cannot handle reading from store of first-class aggregate yet.
853 if (DepSI->getValueOperand()->getType()->isStructTy() ||
854 DepSI->getValueOperand()->getType()->isArrayTy())
855 return -1;
856
857 Value *StorePtr = DepSI->getPointerOperand();
858 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType());
859 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
860 StorePtr, StoreSize, TD);
861 }
862
863 /// AnalyzeLoadFromClobberingLoad - This function is called when we have a
864 /// memdep query of a load that ends up being clobbered by another load. See if
865 /// the other load can feed into the second load.
AnalyzeLoadFromClobberingLoad(Type * LoadTy,Value * LoadPtr,LoadInst * DepLI,const TargetData & TD)866 static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr,
867 LoadInst *DepLI, const TargetData &TD){
868 // Cannot handle reading from store of first-class aggregate yet.
869 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy())
870 return -1;
871
872 Value *DepPtr = DepLI->getPointerOperand();
873 uint64_t DepSize = TD.getTypeSizeInBits(DepLI->getType());
874 int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, TD);
875 if (R != -1) return R;
876
877 // If we have a load/load clobber an DepLI can be widened to cover this load,
878 // then we should widen it!
879 int64_t LoadOffs = 0;
880 const Value *LoadBase =
881 GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, TD);
882 unsigned LoadSize = TD.getTypeStoreSize(LoadTy);
883
884 unsigned Size = MemoryDependenceAnalysis::
885 getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, TD);
886 if (Size == 0) return -1;
887
888 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, TD);
889 }
890
891
892
AnalyzeLoadFromClobberingMemInst(Type * LoadTy,Value * LoadPtr,MemIntrinsic * MI,const TargetData & TD)893 static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
894 MemIntrinsic *MI,
895 const TargetData &TD) {
896 // If the mem operation is a non-constant size, we can't handle it.
897 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
898 if (SizeCst == 0) return -1;
899 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
900
901 // If this is memset, we just need to see if the offset is valid in the size
902 // of the memset..
903 if (MI->getIntrinsicID() == Intrinsic::memset)
904 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
905 MemSizeInBits, TD);
906
907 // If we have a memcpy/memmove, the only case we can handle is if this is a
908 // copy from constant memory. In that case, we can read directly from the
909 // constant memory.
910 MemTransferInst *MTI = cast<MemTransferInst>(MI);
911
912 Constant *Src = dyn_cast<Constant>(MTI->getSource());
913 if (Src == 0) return -1;
914
915 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &TD));
916 if (GV == 0 || !GV->isConstant()) return -1;
917
918 // See if the access is within the bounds of the transfer.
919 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
920 MI->getDest(), MemSizeInBits, TD);
921 if (Offset == -1)
922 return Offset;
923
924 // Otherwise, see if we can constant fold a load from the constant with the
925 // offset applied as appropriate.
926 Src = ConstantExpr::getBitCast(Src,
927 llvm::Type::getInt8PtrTy(Src->getContext()));
928 Constant *OffsetCst =
929 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
930 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst);
931 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
932 if (ConstantFoldLoadFromConstPtr(Src, &TD))
933 return Offset;
934 return -1;
935 }
936
937
938 /// GetStoreValueForLoad - This function is called when we have a
939 /// memdep query of a load that ends up being a clobbering store. This means
940 /// that the store provides bits used by the load but we the pointers don't
941 /// mustalias. Check this case to see if there is anything more we can do
942 /// before we give up.
GetStoreValueForLoad(Value * SrcVal,unsigned Offset,Type * LoadTy,Instruction * InsertPt,const TargetData & TD)943 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
944 Type *LoadTy,
945 Instruction *InsertPt, const TargetData &TD){
946 LLVMContext &Ctx = SrcVal->getType()->getContext();
947
948 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
949 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
950
951 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
952
953 // Compute which bits of the stored value are being used by the load. Convert
954 // to an integer type to start with.
955 if (SrcVal->getType()->isPointerTy())
956 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx));
957 if (!SrcVal->getType()->isIntegerTy())
958 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8));
959
960 // Shift the bits to the least significant depending on endianness.
961 unsigned ShiftAmt;
962 if (TD.isLittleEndian())
963 ShiftAmt = Offset*8;
964 else
965 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
966
967 if (ShiftAmt)
968 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt);
969
970 if (LoadSize != StoreSize)
971 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8));
972
973 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
974 }
975
976 /// GetStoreValueForLoad - This function is called when we have a
977 /// memdep query of a load that ends up being a clobbering load. This means
978 /// that the load *may* provide bits used by the load but we can't be sure
979 /// because the pointers don't mustalias. Check this case to see if there is
980 /// anything more we can do before we give up.
GetLoadValueForLoad(LoadInst * SrcVal,unsigned Offset,Type * LoadTy,Instruction * InsertPt,GVN & gvn)981 static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset,
982 Type *LoadTy, Instruction *InsertPt,
983 GVN &gvn) {
984 const TargetData &TD = *gvn.getTargetData();
985 // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to
986 // widen SrcVal out to a larger load.
987 unsigned SrcValSize = TD.getTypeStoreSize(SrcVal->getType());
988 unsigned LoadSize = TD.getTypeStoreSize(LoadTy);
989 if (Offset+LoadSize > SrcValSize) {
990 assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!");
991 assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load");
992 // If we have a load/load clobber an DepLI can be widened to cover this
993 // load, then we should widen it to the next power of 2 size big enough!
994 unsigned NewLoadSize = Offset+LoadSize;
995 if (!isPowerOf2_32(NewLoadSize))
996 NewLoadSize = NextPowerOf2(NewLoadSize);
997
998 Value *PtrVal = SrcVal->getPointerOperand();
999
1000 // Insert the new load after the old load. This ensures that subsequent
1001 // memdep queries will find the new load. We can't easily remove the old
1002 // load completely because it is already in the value numbering table.
1003 IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal));
1004 Type *DestPTy =
1005 IntegerType::get(LoadTy->getContext(), NewLoadSize*8);
1006 DestPTy = PointerType::get(DestPTy,
1007 cast<PointerType>(PtrVal->getType())->getAddressSpace());
1008 Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc());
1009 PtrVal = Builder.CreateBitCast(PtrVal, DestPTy);
1010 LoadInst *NewLoad = Builder.CreateLoad(PtrVal);
1011 NewLoad->takeName(SrcVal);
1012 NewLoad->setAlignment(SrcVal->getAlignment());
1013
1014 DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n");
1015 DEBUG(dbgs() << "TO: " << *NewLoad << "\n");
1016
1017 // Replace uses of the original load with the wider load. On a big endian
1018 // system, we need to shift down to get the relevant bits.
1019 Value *RV = NewLoad;
1020 if (TD.isBigEndian())
1021 RV = Builder.CreateLShr(RV,
1022 NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits());
1023 RV = Builder.CreateTrunc(RV, SrcVal->getType());
1024 SrcVal->replaceAllUsesWith(RV);
1025
1026 // We would like to use gvn.markInstructionForDeletion here, but we can't
1027 // because the load is already memoized into the leader map table that GVN
1028 // tracks. It is potentially possible to remove the load from the table,
1029 // but then there all of the operations based on it would need to be
1030 // rehashed. Just leave the dead load around.
1031 gvn.getMemDep().removeInstruction(SrcVal);
1032 SrcVal = NewLoad;
1033 }
1034
1035 return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, TD);
1036 }
1037
1038
1039 /// GetMemInstValueForLoad - This function is called when we have a
1040 /// memdep query of a load that ends up being a clobbering mem intrinsic.
GetMemInstValueForLoad(MemIntrinsic * SrcInst,unsigned Offset,Type * LoadTy,Instruction * InsertPt,const TargetData & TD)1041 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1042 Type *LoadTy, Instruction *InsertPt,
1043 const TargetData &TD){
1044 LLVMContext &Ctx = LoadTy->getContext();
1045 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1046
1047 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1048
1049 // We know that this method is only called when the mem transfer fully
1050 // provides the bits for the load.
1051 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1052 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1053 // independently of what the offset is.
1054 Value *Val = MSI->getValue();
1055 if (LoadSize != 1)
1056 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1057
1058 Value *OneElt = Val;
1059
1060 // Splat the value out to the right number of bits.
1061 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1062 // If we can double the number of bytes set, do it.
1063 if (NumBytesSet*2 <= LoadSize) {
1064 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1065 Val = Builder.CreateOr(Val, ShVal);
1066 NumBytesSet <<= 1;
1067 continue;
1068 }
1069
1070 // Otherwise insert one byte at a time.
1071 Value *ShVal = Builder.CreateShl(Val, 1*8);
1072 Val = Builder.CreateOr(OneElt, ShVal);
1073 ++NumBytesSet;
1074 }
1075
1076 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1077 }
1078
1079 // Otherwise, this is a memcpy/memmove from a constant global.
1080 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1081 Constant *Src = cast<Constant>(MTI->getSource());
1082
1083 // Otherwise, see if we can constant fold a load from the constant with the
1084 // offset applied as appropriate.
1085 Src = ConstantExpr::getBitCast(Src,
1086 llvm::Type::getInt8PtrTy(Src->getContext()));
1087 Constant *OffsetCst =
1088 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1089 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst);
1090 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1091 return ConstantFoldLoadFromConstPtr(Src, &TD);
1092 }
1093
1094 namespace {
1095
1096 struct AvailableValueInBlock {
1097 /// BB - The basic block in question.
1098 BasicBlock *BB;
1099 enum ValType {
1100 SimpleVal, // A simple offsetted value that is accessed.
1101 LoadVal, // A value produced by a load.
1102 MemIntrin // A memory intrinsic which is loaded from.
1103 };
1104
1105 /// V - The value that is live out of the block.
1106 PointerIntPair<Value *, 2, ValType> Val;
1107
1108 /// Offset - The byte offset in Val that is interesting for the load query.
1109 unsigned Offset;
1110
get__anond0db39690311::AvailableValueInBlock1111 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1112 unsigned Offset = 0) {
1113 AvailableValueInBlock Res;
1114 Res.BB = BB;
1115 Res.Val.setPointer(V);
1116 Res.Val.setInt(SimpleVal);
1117 Res.Offset = Offset;
1118 return Res;
1119 }
1120
getMI__anond0db39690311::AvailableValueInBlock1121 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1122 unsigned Offset = 0) {
1123 AvailableValueInBlock Res;
1124 Res.BB = BB;
1125 Res.Val.setPointer(MI);
1126 Res.Val.setInt(MemIntrin);
1127 Res.Offset = Offset;
1128 return Res;
1129 }
1130
getLoad__anond0db39690311::AvailableValueInBlock1131 static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI,
1132 unsigned Offset = 0) {
1133 AvailableValueInBlock Res;
1134 Res.BB = BB;
1135 Res.Val.setPointer(LI);
1136 Res.Val.setInt(LoadVal);
1137 Res.Offset = Offset;
1138 return Res;
1139 }
1140
isSimpleValue__anond0db39690311::AvailableValueInBlock1141 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
isCoercedLoadValue__anond0db39690311::AvailableValueInBlock1142 bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; }
isMemIntrinValue__anond0db39690311::AvailableValueInBlock1143 bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; }
1144
getSimpleValue__anond0db39690311::AvailableValueInBlock1145 Value *getSimpleValue() const {
1146 assert(isSimpleValue() && "Wrong accessor");
1147 return Val.getPointer();
1148 }
1149
getCoercedLoadValue__anond0db39690311::AvailableValueInBlock1150 LoadInst *getCoercedLoadValue() const {
1151 assert(isCoercedLoadValue() && "Wrong accessor");
1152 return cast<LoadInst>(Val.getPointer());
1153 }
1154
getMemIntrinValue__anond0db39690311::AvailableValueInBlock1155 MemIntrinsic *getMemIntrinValue() const {
1156 assert(isMemIntrinValue() && "Wrong accessor");
1157 return cast<MemIntrinsic>(Val.getPointer());
1158 }
1159
1160 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1161 /// defined here to the specified type. This handles various coercion cases.
MaterializeAdjustedValue__anond0db39690311::AvailableValueInBlock1162 Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const {
1163 Value *Res;
1164 if (isSimpleValue()) {
1165 Res = getSimpleValue();
1166 if (Res->getType() != LoadTy) {
1167 const TargetData *TD = gvn.getTargetData();
1168 assert(TD && "Need target data to handle type mismatch case");
1169 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1170 *TD);
1171
1172 DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1173 << *getSimpleValue() << '\n'
1174 << *Res << '\n' << "\n\n\n");
1175 }
1176 } else if (isCoercedLoadValue()) {
1177 LoadInst *Load = getCoercedLoadValue();
1178 if (Load->getType() == LoadTy && Offset == 0) {
1179 Res = Load;
1180 } else {
1181 Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(),
1182 gvn);
1183
1184 DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " "
1185 << *getCoercedLoadValue() << '\n'
1186 << *Res << '\n' << "\n\n\n");
1187 }
1188 } else {
1189 const TargetData *TD = gvn.getTargetData();
1190 assert(TD && "Need target data to handle type mismatch case");
1191 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1192 LoadTy, BB->getTerminator(), *TD);
1193 DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1194 << " " << *getMemIntrinValue() << '\n'
1195 << *Res << '\n' << "\n\n\n");
1196 }
1197 return Res;
1198 }
1199 };
1200
1201 } // end anonymous namespace
1202
1203 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1204 /// construct SSA form, allowing us to eliminate LI. This returns the value
1205 /// that should be used at LI's definition site.
ConstructSSAForLoadSet(LoadInst * LI,SmallVectorImpl<AvailableValueInBlock> & ValuesPerBlock,GVN & gvn)1206 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1207 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1208 GVN &gvn) {
1209 // Check for the fully redundant, dominating load case. In this case, we can
1210 // just use the dominating value directly.
1211 if (ValuesPerBlock.size() == 1 &&
1212 gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB,
1213 LI->getParent()))
1214 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn);
1215
1216 // Otherwise, we have to construct SSA form.
1217 SmallVector<PHINode*, 8> NewPHIs;
1218 SSAUpdater SSAUpdate(&NewPHIs);
1219 SSAUpdate.Initialize(LI->getType(), LI->getName());
1220
1221 Type *LoadTy = LI->getType();
1222
1223 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1224 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1225 BasicBlock *BB = AV.BB;
1226
1227 if (SSAUpdate.HasValueForBlock(BB))
1228 continue;
1229
1230 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn));
1231 }
1232
1233 // Perform PHI construction.
1234 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1235
1236 // If new PHI nodes were created, notify alias analysis.
1237 if (V->getType()->isPointerTy()) {
1238 AliasAnalysis *AA = gvn.getAliasAnalysis();
1239
1240 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1241 AA->copyValue(LI, NewPHIs[i]);
1242
1243 // Now that we've copied information to the new PHIs, scan through
1244 // them again and inform alias analysis that we've added potentially
1245 // escaping uses to any values that are operands to these PHIs.
1246 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) {
1247 PHINode *P = NewPHIs[i];
1248 for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) {
1249 unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
1250 AA->addEscapingUse(P->getOperandUse(jj));
1251 }
1252 }
1253 }
1254
1255 return V;
1256 }
1257
isLifetimeStart(const Instruction * Inst)1258 static bool isLifetimeStart(const Instruction *Inst) {
1259 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1260 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1261 return false;
1262 }
1263
1264 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1265 /// non-local by performing PHI construction.
processNonLocalLoad(LoadInst * LI)1266 bool GVN::processNonLocalLoad(LoadInst *LI) {
1267 // Find the non-local dependencies of the load.
1268 SmallVector<NonLocalDepResult, 64> Deps;
1269 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI);
1270 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps);
1271 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1272 // << Deps.size() << *LI << '\n');
1273
1274 // If we had to process more than one hundred blocks to find the
1275 // dependencies, this load isn't worth worrying about. Optimizing
1276 // it will be too expensive.
1277 if (Deps.size() > 100)
1278 return false;
1279
1280 // If we had a phi translation failure, we'll have a single entry which is a
1281 // clobber in the current block. Reject this early.
1282 if (Deps.size() == 1
1283 && !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber())
1284 {
1285 DEBUG(
1286 dbgs() << "GVN: non-local load ";
1287 WriteAsOperand(dbgs(), LI);
1288 dbgs() << " has unknown dependencies\n";
1289 );
1290 return false;
1291 }
1292
1293 // Filter out useless results (non-locals, etc). Keep track of the blocks
1294 // where we have a value available in repl, also keep track of whether we see
1295 // dependencies that produce an unknown value for the load (such as a call
1296 // that could potentially clobber the load).
1297 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1298 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1299
1300 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1301 BasicBlock *DepBB = Deps[i].getBB();
1302 MemDepResult DepInfo = Deps[i].getResult();
1303
1304 if (!DepInfo.isDef() && !DepInfo.isClobber()) {
1305 UnavailableBlocks.push_back(DepBB);
1306 continue;
1307 }
1308
1309 if (DepInfo.isClobber()) {
1310 // The address being loaded in this non-local block may not be the same as
1311 // the pointer operand of the load if PHI translation occurs. Make sure
1312 // to consider the right address.
1313 Value *Address = Deps[i].getAddress();
1314
1315 // If the dependence is to a store that writes to a superset of the bits
1316 // read by the load, we can extract the bits we need for the load from the
1317 // stored value.
1318 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1319 if (TD && Address) {
1320 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1321 DepSI, *TD);
1322 if (Offset != -1) {
1323 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1324 DepSI->getValueOperand(),
1325 Offset));
1326 continue;
1327 }
1328 }
1329 }
1330
1331 // Check to see if we have something like this:
1332 // load i32* P
1333 // load i8* (P+1)
1334 // if we have this, replace the later with an extraction from the former.
1335 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) {
1336 // If this is a clobber and L is the first instruction in its block, then
1337 // we have the first instruction in the entry block.
1338 if (DepLI != LI && Address && TD) {
1339 int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(),
1340 LI->getPointerOperand(),
1341 DepLI, *TD);
1342
1343 if (Offset != -1) {
1344 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI,
1345 Offset));
1346 continue;
1347 }
1348 }
1349 }
1350
1351 // If the clobbering value is a memset/memcpy/memmove, see if we can
1352 // forward a value on from it.
1353 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1354 if (TD && Address) {
1355 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1356 DepMI, *TD);
1357 if (Offset != -1) {
1358 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1359 Offset));
1360 continue;
1361 }
1362 }
1363 }
1364
1365 UnavailableBlocks.push_back(DepBB);
1366 continue;
1367 }
1368
1369 // DepInfo.isDef() here
1370
1371 Instruction *DepInst = DepInfo.getInst();
1372
1373 // Loading the allocation -> undef.
1374 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1375 // Loading immediately after lifetime begin -> undef.
1376 isLifetimeStart(DepInst)) {
1377 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1378 UndefValue::get(LI->getType())));
1379 continue;
1380 }
1381
1382 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1383 // Reject loads and stores that are to the same address but are of
1384 // different types if we have to.
1385 if (S->getValueOperand()->getType() != LI->getType()) {
1386 // If the stored value is larger or equal to the loaded value, we can
1387 // reuse it.
1388 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(),
1389 LI->getType(), *TD)) {
1390 UnavailableBlocks.push_back(DepBB);
1391 continue;
1392 }
1393 }
1394
1395 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1396 S->getValueOperand()));
1397 continue;
1398 }
1399
1400 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1401 // If the types mismatch and we can't handle it, reject reuse of the load.
1402 if (LD->getType() != LI->getType()) {
1403 // If the stored value is larger or equal to the loaded value, we can
1404 // reuse it.
1405 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1406 UnavailableBlocks.push_back(DepBB);
1407 continue;
1408 }
1409 }
1410 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD));
1411 continue;
1412 }
1413
1414 UnavailableBlocks.push_back(DepBB);
1415 continue;
1416 }
1417
1418 // If we have no predecessors that produce a known value for this load, exit
1419 // early.
1420 if (ValuesPerBlock.empty()) return false;
1421
1422 // If all of the instructions we depend on produce a known value for this
1423 // load, then it is fully redundant and we can use PHI insertion to compute
1424 // its value. Insert PHIs and remove the fully redundant value now.
1425 if (UnavailableBlocks.empty()) {
1426 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1427
1428 // Perform PHI construction.
1429 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
1430 LI->replaceAllUsesWith(V);
1431
1432 if (isa<PHINode>(V))
1433 V->takeName(LI);
1434 if (V->getType()->isPointerTy())
1435 MD->invalidateCachedPointerInfo(V);
1436 markInstructionForDeletion(LI);
1437 ++NumGVNLoad;
1438 return true;
1439 }
1440
1441 if (!EnablePRE || !EnableLoadPRE)
1442 return false;
1443
1444 // Okay, we have *some* definitions of the value. This means that the value
1445 // is available in some of our (transitive) predecessors. Lets think about
1446 // doing PRE of this load. This will involve inserting a new load into the
1447 // predecessor when it's not available. We could do this in general, but
1448 // prefer to not increase code size. As such, we only do this when we know
1449 // that we only have to insert *one* load (which means we're basically moving
1450 // the load, not inserting a new one).
1451
1452 SmallPtrSet<BasicBlock *, 4> Blockers;
1453 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1454 Blockers.insert(UnavailableBlocks[i]);
1455
1456 // Let's find the first basic block with more than one predecessor. Walk
1457 // backwards through predecessors if needed.
1458 BasicBlock *LoadBB = LI->getParent();
1459 BasicBlock *TmpBB = LoadBB;
1460
1461 bool isSinglePred = false;
1462 bool allSingleSucc = true;
1463 while (TmpBB->getSinglePredecessor()) {
1464 isSinglePred = true;
1465 TmpBB = TmpBB->getSinglePredecessor();
1466 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1467 return false;
1468 if (Blockers.count(TmpBB))
1469 return false;
1470
1471 // If any of these blocks has more than one successor (i.e. if the edge we
1472 // just traversed was critical), then there are other paths through this
1473 // block along which the load may not be anticipated. Hoisting the load
1474 // above this block would be adding the load to execution paths along
1475 // which it was not previously executed.
1476 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1477 return false;
1478 }
1479
1480 assert(TmpBB);
1481 LoadBB = TmpBB;
1482
1483 // FIXME: It is extremely unclear what this loop is doing, other than
1484 // artificially restricting loadpre.
1485 if (isSinglePred) {
1486 bool isHot = false;
1487 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1488 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1489 if (AV.isSimpleValue())
1490 // "Hot" Instruction is in some loop (because it dominates its dep.
1491 // instruction).
1492 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1493 if (DT->dominates(LI, I)) {
1494 isHot = true;
1495 break;
1496 }
1497 }
1498
1499 // We are interested only in "hot" instructions. We don't want to do any
1500 // mis-optimizations here.
1501 if (!isHot)
1502 return false;
1503 }
1504
1505 // Check to see how many predecessors have the loaded value fully
1506 // available.
1507 DenseMap<BasicBlock*, Value*> PredLoads;
1508 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1509 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1510 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1511 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1512 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1513
1514 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1515 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1516 PI != E; ++PI) {
1517 BasicBlock *Pred = *PI;
1518 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1519 continue;
1520 }
1521 PredLoads[Pred] = 0;
1522
1523 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1524 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1525 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1526 << Pred->getName() << "': " << *LI << '\n');
1527 return false;
1528 }
1529
1530 if (LoadBB->isLandingPad()) {
1531 DEBUG(dbgs()
1532 << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '"
1533 << Pred->getName() << "': " << *LI << '\n');
1534 return false;
1535 }
1536
1537 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1538 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1539 }
1540 }
1541
1542 if (!NeedToSplit.empty()) {
1543 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1544 return false;
1545 }
1546
1547 // Decide whether PRE is profitable for this load.
1548 unsigned NumUnavailablePreds = PredLoads.size();
1549 assert(NumUnavailablePreds != 0 &&
1550 "Fully available value should be eliminated above!");
1551
1552 // If this load is unavailable in multiple predecessors, reject it.
1553 // FIXME: If we could restructure the CFG, we could make a common pred with
1554 // all the preds that don't have an available LI and insert a new load into
1555 // that one block.
1556 if (NumUnavailablePreds != 1)
1557 return false;
1558
1559 // Check if the load can safely be moved to all the unavailable predecessors.
1560 bool CanDoPRE = true;
1561 SmallVector<Instruction*, 8> NewInsts;
1562 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1563 E = PredLoads.end(); I != E; ++I) {
1564 BasicBlock *UnavailablePred = I->first;
1565
1566 // Do PHI translation to get its value in the predecessor if necessary. The
1567 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1568
1569 // If all preds have a single successor, then we know it is safe to insert
1570 // the load on the pred (?!?), so we can insert code to materialize the
1571 // pointer if it is not available.
1572 PHITransAddr Address(LI->getPointerOperand(), TD);
1573 Value *LoadPtr = 0;
1574 if (allSingleSucc) {
1575 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1576 *DT, NewInsts);
1577 } else {
1578 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1579 LoadPtr = Address.getAddr();
1580 }
1581
1582 // If we couldn't find or insert a computation of this phi translated value,
1583 // we fail PRE.
1584 if (LoadPtr == 0) {
1585 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1586 << *LI->getPointerOperand() << "\n");
1587 CanDoPRE = false;
1588 break;
1589 }
1590
1591 // Make sure it is valid to move this load here. We have to watch out for:
1592 // @1 = getelementptr (i8* p, ...
1593 // test p and branch if == 0
1594 // load @1
1595 // It is valid to have the getelementptr before the test, even if p can
1596 // be 0, as getelementptr only does address arithmetic.
1597 // If we are not pushing the value through any multiple-successor blocks
1598 // we do not have this case. Otherwise, check that the load is safe to
1599 // put anywhere; this can be improved, but should be conservatively safe.
1600 if (!allSingleSucc &&
1601 // FIXME: REEVALUTE THIS.
1602 !isSafeToLoadUnconditionally(LoadPtr,
1603 UnavailablePred->getTerminator(),
1604 LI->getAlignment(), TD)) {
1605 CanDoPRE = false;
1606 break;
1607 }
1608
1609 I->second = LoadPtr;
1610 }
1611
1612 if (!CanDoPRE) {
1613 while (!NewInsts.empty()) {
1614 Instruction *I = NewInsts.pop_back_val();
1615 if (MD) MD->removeInstruction(I);
1616 I->eraseFromParent();
1617 }
1618 return false;
1619 }
1620
1621 // Okay, we can eliminate this load by inserting a reload in the predecessor
1622 // and using PHI construction to get the value in the other predecessors, do
1623 // it.
1624 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1625 DEBUG(if (!NewInsts.empty())
1626 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1627 << *NewInsts.back() << '\n');
1628
1629 // Assign value numbers to the new instructions.
1630 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1631 // FIXME: We really _ought_ to insert these value numbers into their
1632 // parent's availability map. However, in doing so, we risk getting into
1633 // ordering issues. If a block hasn't been processed yet, we would be
1634 // marking a value as AVAIL-IN, which isn't what we intend.
1635 VN.lookup_or_add(NewInsts[i]);
1636 }
1637
1638 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1639 E = PredLoads.end(); I != E; ++I) {
1640 BasicBlock *UnavailablePred = I->first;
1641 Value *LoadPtr = I->second;
1642
1643 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1644 LI->getAlignment(),
1645 UnavailablePred->getTerminator());
1646
1647 // Transfer the old load's TBAA tag to the new load.
1648 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa))
1649 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag);
1650
1651 // Transfer DebugLoc.
1652 NewLoad->setDebugLoc(LI->getDebugLoc());
1653
1654 // Add the newly created load.
1655 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1656 NewLoad));
1657 MD->invalidateCachedPointerInfo(LoadPtr);
1658 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1659 }
1660
1661 // Perform PHI construction.
1662 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
1663 LI->replaceAllUsesWith(V);
1664 if (isa<PHINode>(V))
1665 V->takeName(LI);
1666 if (V->getType()->isPointerTy())
1667 MD->invalidateCachedPointerInfo(V);
1668 markInstructionForDeletion(LI);
1669 ++NumPRELoad;
1670 return true;
1671 }
1672
1673 /// processLoad - Attempt to eliminate a load, first by eliminating it
1674 /// locally, and then attempting non-local elimination if that fails.
processLoad(LoadInst * L)1675 bool GVN::processLoad(LoadInst *L) {
1676 if (!MD)
1677 return false;
1678
1679 if (!L->isSimple())
1680 return false;
1681
1682 if (L->use_empty()) {
1683 markInstructionForDeletion(L);
1684 return true;
1685 }
1686
1687 // ... to a pointer that has been loaded from before...
1688 MemDepResult Dep = MD->getDependency(L);
1689
1690 // If we have a clobber and target data is around, see if this is a clobber
1691 // that we can fix up through code synthesis.
1692 if (Dep.isClobber() && TD) {
1693 // Check to see if we have something like this:
1694 // store i32 123, i32* %P
1695 // %A = bitcast i32* %P to i8*
1696 // %B = gep i8* %A, i32 1
1697 // %C = load i8* %B
1698 //
1699 // We could do that by recognizing if the clobber instructions are obviously
1700 // a common base + constant offset, and if the previous store (or memset)
1701 // completely covers this load. This sort of thing can happen in bitfield
1702 // access code.
1703 Value *AvailVal = 0;
1704 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) {
1705 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1706 L->getPointerOperand(),
1707 DepSI, *TD);
1708 if (Offset != -1)
1709 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset,
1710 L->getType(), L, *TD);
1711 }
1712
1713 // Check to see if we have something like this:
1714 // load i32* P
1715 // load i8* (P+1)
1716 // if we have this, replace the later with an extraction from the former.
1717 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) {
1718 // If this is a clobber and L is the first instruction in its block, then
1719 // we have the first instruction in the entry block.
1720 if (DepLI == L)
1721 return false;
1722
1723 int Offset = AnalyzeLoadFromClobberingLoad(L->getType(),
1724 L->getPointerOperand(),
1725 DepLI, *TD);
1726 if (Offset != -1)
1727 AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this);
1728 }
1729
1730 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1731 // a value on from it.
1732 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1733 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1734 L->getPointerOperand(),
1735 DepMI, *TD);
1736 if (Offset != -1)
1737 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *TD);
1738 }
1739
1740 if (AvailVal) {
1741 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1742 << *AvailVal << '\n' << *L << "\n\n\n");
1743
1744 // Replace the load!
1745 L->replaceAllUsesWith(AvailVal);
1746 if (AvailVal->getType()->isPointerTy())
1747 MD->invalidateCachedPointerInfo(AvailVal);
1748 markInstructionForDeletion(L);
1749 ++NumGVNLoad;
1750 return true;
1751 }
1752 }
1753
1754 // If the value isn't available, don't do anything!
1755 if (Dep.isClobber()) {
1756 DEBUG(
1757 // fast print dep, using operator<< on instruction is too slow.
1758 dbgs() << "GVN: load ";
1759 WriteAsOperand(dbgs(), L);
1760 Instruction *I = Dep.getInst();
1761 dbgs() << " is clobbered by " << *I << '\n';
1762 );
1763 return false;
1764 }
1765
1766 // If it is defined in another block, try harder.
1767 if (Dep.isNonLocal())
1768 return processNonLocalLoad(L);
1769
1770 if (!Dep.isDef()) {
1771 DEBUG(
1772 // fast print dep, using operator<< on instruction is too slow.
1773 dbgs() << "GVN: load ";
1774 WriteAsOperand(dbgs(), L);
1775 dbgs() << " has unknown dependence\n";
1776 );
1777 return false;
1778 }
1779
1780 Instruction *DepInst = Dep.getInst();
1781 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1782 Value *StoredVal = DepSI->getValueOperand();
1783
1784 // The store and load are to a must-aliased pointer, but they may not
1785 // actually have the same type. See if we know how to reuse the stored
1786 // value (depending on its type).
1787 if (StoredVal->getType() != L->getType()) {
1788 if (TD) {
1789 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1790 L, *TD);
1791 if (StoredVal == 0)
1792 return false;
1793
1794 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1795 << '\n' << *L << "\n\n\n");
1796 }
1797 else
1798 return false;
1799 }
1800
1801 // Remove it!
1802 L->replaceAllUsesWith(StoredVal);
1803 if (StoredVal->getType()->isPointerTy())
1804 MD->invalidateCachedPointerInfo(StoredVal);
1805 markInstructionForDeletion(L);
1806 ++NumGVNLoad;
1807 return true;
1808 }
1809
1810 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1811 Value *AvailableVal = DepLI;
1812
1813 // The loads are of a must-aliased pointer, but they may not actually have
1814 // the same type. See if we know how to reuse the previously loaded value
1815 // (depending on its type).
1816 if (DepLI->getType() != L->getType()) {
1817 if (TD) {
1818 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(),
1819 L, *TD);
1820 if (AvailableVal == 0)
1821 return false;
1822
1823 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1824 << "\n" << *L << "\n\n\n");
1825 }
1826 else
1827 return false;
1828 }
1829
1830 // Remove it!
1831 L->replaceAllUsesWith(AvailableVal);
1832 if (DepLI->getType()->isPointerTy())
1833 MD->invalidateCachedPointerInfo(DepLI);
1834 markInstructionForDeletion(L);
1835 ++NumGVNLoad;
1836 return true;
1837 }
1838
1839 // If this load really doesn't depend on anything, then we must be loading an
1840 // undef value. This can happen when loading for a fresh allocation with no
1841 // intervening stores, for example.
1842 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1843 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1844 markInstructionForDeletion(L);
1845 ++NumGVNLoad;
1846 return true;
1847 }
1848
1849 // If this load occurs either right after a lifetime begin,
1850 // then the loaded value is undefined.
1851 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) {
1852 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1853 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1854 markInstructionForDeletion(L);
1855 ++NumGVNLoad;
1856 return true;
1857 }
1858 }
1859
1860 return false;
1861 }
1862
1863 // findLeader - In order to find a leader for a given value number at a
1864 // specific basic block, we first obtain the list of all Values for that number,
1865 // and then scan the list to find one whose block dominates the block in
1866 // question. This is fast because dominator tree queries consist of only
1867 // a few comparisons of DFS numbers.
findLeader(BasicBlock * BB,uint32_t num)1868 Value *GVN::findLeader(BasicBlock *BB, uint32_t num) {
1869 LeaderTableEntry Vals = LeaderTable[num];
1870 if (!Vals.Val) return 0;
1871
1872 Value *Val = 0;
1873 if (DT->dominates(Vals.BB, BB)) {
1874 Val = Vals.Val;
1875 if (isa<Constant>(Val)) return Val;
1876 }
1877
1878 LeaderTableEntry* Next = Vals.Next;
1879 while (Next) {
1880 if (DT->dominates(Next->BB, BB)) {
1881 if (isa<Constant>(Next->Val)) return Next->Val;
1882 if (!Val) Val = Next->Val;
1883 }
1884
1885 Next = Next->Next;
1886 }
1887
1888 return Val;
1889 }
1890
1891 /// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the
1892 /// use is dominated by the given basic block. Returns the number of uses that
1893 /// were replaced.
replaceAllDominatedUsesWith(Value * From,Value * To,BasicBlock * Root)1894 unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
1895 BasicBlock *Root) {
1896 unsigned Count = 0;
1897 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1898 UI != UE; ) {
1899 Instruction *User = cast<Instruction>(*UI);
1900 unsigned OpNum = UI.getOperandNo();
1901 ++UI;
1902
1903 if (DT->dominates(Root, User->getParent())) {
1904 User->setOperand(OpNum, To);
1905 ++Count;
1906 }
1907 }
1908 return Count;
1909 }
1910
1911 /// propagateEquality - The given values are known to be equal in every block
1912 /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
1913 /// 'RHS' everywhere in the scope. Returns whether a change was made.
propagateEquality(Value * LHS,Value * RHS,BasicBlock * Root)1914 bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) {
1915 if (LHS == RHS) return false;
1916 assert(LHS->getType() == RHS->getType() && "Equal but types differ!");
1917
1918 // Don't try to propagate equalities between constants.
1919 if (isa<Constant>(LHS) && isa<Constant>(RHS))
1920 return false;
1921
1922 // Make sure that any constants are on the right-hand side. In general the
1923 // best results are obtained by placing the longest lived value on the RHS.
1924 if (isa<Constant>(LHS))
1925 std::swap(LHS, RHS);
1926
1927 // If neither term is constant then bail out. This is not for correctness,
1928 // it's just that the non-constant case is much less useful: it occurs just
1929 // as often as the constant case but handling it hardly ever results in an
1930 // improvement.
1931 if (!isa<Constant>(RHS))
1932 return false;
1933
1934 // If value numbering later deduces that an instruction in the scope is equal
1935 // to 'LHS' then ensure it will be turned into 'RHS'.
1936 addToLeaderTable(VN.lookup_or_add(LHS), RHS, Root);
1937
1938 // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope.
1939 unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
1940 bool Changed = NumReplacements > 0;
1941 NumGVNEqProp += NumReplacements;
1942
1943 // Now try to deduce additional equalities from this one. For example, if the
1944 // known equality was "(A != B)" == "false" then it follows that A and B are
1945 // equal in the scope. Only boolean equalities with an explicit true or false
1946 // RHS are currently supported.
1947 if (!RHS->getType()->isIntegerTy(1))
1948 // Not a boolean equality - bail out.
1949 return Changed;
1950 ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
1951 if (!CI)
1952 // RHS neither 'true' nor 'false' - bail out.
1953 return Changed;
1954 // Whether RHS equals 'true'. Otherwise it equals 'false'.
1955 bool isKnownTrue = CI->isAllOnesValue();
1956 bool isKnownFalse = !isKnownTrue;
1957
1958 // If "A && B" is known true then both A and B are known true. If "A || B"
1959 // is known false then both A and B are known false.
1960 Value *A, *B;
1961 if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
1962 (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
1963 Changed |= propagateEquality(A, RHS, Root);
1964 Changed |= propagateEquality(B, RHS, Root);
1965 return Changed;
1966 }
1967
1968 // If we are propagating an equality like "(A == B)" == "true" then also
1969 // propagate the equality A == B.
1970 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
1971 // Only equality comparisons are supported.
1972 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
1973 (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) {
1974 Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
1975 Changed |= propagateEquality(Op0, Op1, Root);
1976 }
1977 return Changed;
1978 }
1979
1980 return Changed;
1981 }
1982
1983 /// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return
1984 /// true if every path from the entry block to 'Dst' passes via this edge. In
1985 /// particular 'Dst' must not be reachable via another edge from 'Src'.
isOnlyReachableViaThisEdge(BasicBlock * Src,BasicBlock * Dst,DominatorTree * DT)1986 static bool isOnlyReachableViaThisEdge(BasicBlock *Src, BasicBlock *Dst,
1987 DominatorTree *DT) {
1988 // First off, there must not be more than one edge from Src to Dst, there
1989 // should be exactly one. So keep track of the number of times Src occurs
1990 // as a predecessor of Dst and fail if it's more than once. Secondly, any
1991 // other predecessors of Dst should be dominated by Dst (see logic below).
1992 bool SawEdgeFromSrc = false;
1993 for (pred_iterator PI = pred_begin(Dst), PE = pred_end(Dst); PI != PE; ++PI) {
1994 BasicBlock *Pred = *PI;
1995 if (Pred == Src) {
1996 // An edge from Src to Dst.
1997 if (SawEdgeFromSrc)
1998 // There are multiple edges from Src to Dst - fail.
1999 return false;
2000 SawEdgeFromSrc = true;
2001 continue;
2002 }
2003 // If the predecessor is not dominated by Dst, then it must be possible to
2004 // reach it either without passing through Src (and thus not via the edge)
2005 // or by passing through Src but taking a different edge out of Src. Either
2006 // way it is possible to reach Dst without passing via the edge, so fail.
2007 if (!DT->dominates(Dst, *PI))
2008 return false;
2009 }
2010 assert(SawEdgeFromSrc && "No edge between these basic blocks!");
2011
2012 // Every path from the entry block to Dst must at some point pass to Dst from
2013 // a predecessor that is not dominated by Dst. This predecessor can only be
2014 // Src, since all others are dominated by Dst. As there is only one edge from
2015 // Src to Dst, the path passes by this edge.
2016 return true;
2017 }
2018
2019 /// processInstruction - When calculating availability, handle an instruction
2020 /// by inserting it into the appropriate sets
processInstruction(Instruction * I)2021 bool GVN::processInstruction(Instruction *I) {
2022 // Ignore dbg info intrinsics.
2023 if (isa<DbgInfoIntrinsic>(I))
2024 return false;
2025
2026 // If the instruction can be easily simplified then do so now in preference
2027 // to value numbering it. Value numbering often exposes redundancies, for
2028 // example if it determines that %y is equal to %x then the instruction
2029 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify.
2030 if (Value *V = SimplifyInstruction(I, TD, DT)) {
2031 I->replaceAllUsesWith(V);
2032 if (MD && V->getType()->isPointerTy())
2033 MD->invalidateCachedPointerInfo(V);
2034 markInstructionForDeletion(I);
2035 ++NumGVNSimpl;
2036 return true;
2037 }
2038
2039 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
2040 if (processLoad(LI))
2041 return true;
2042
2043 unsigned Num = VN.lookup_or_add(LI);
2044 addToLeaderTable(Num, LI, LI->getParent());
2045 return false;
2046 }
2047
2048 // For conditional branches, we can perform simple conditional propagation on
2049 // the condition value itself.
2050 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
2051 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
2052 return false;
2053
2054 Value *BranchCond = BI->getCondition();
2055
2056 BasicBlock *TrueSucc = BI->getSuccessor(0);
2057 BasicBlock *FalseSucc = BI->getSuccessor(1);
2058 BasicBlock *Parent = BI->getParent();
2059 bool Changed = false;
2060
2061 if (isOnlyReachableViaThisEdge(Parent, TrueSucc, DT))
2062 Changed |= propagateEquality(BranchCond,
2063 ConstantInt::getTrue(TrueSucc->getContext()),
2064 TrueSucc);
2065
2066 if (isOnlyReachableViaThisEdge(Parent, FalseSucc, DT))
2067 Changed |= propagateEquality(BranchCond,
2068 ConstantInt::getFalse(FalseSucc->getContext()),
2069 FalseSucc);
2070
2071 return Changed;
2072 }
2073
2074 // For switches, propagate the case values into the case destinations.
2075 if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
2076 Value *SwitchCond = SI->getCondition();
2077 BasicBlock *Parent = SI->getParent();
2078 bool Changed = false;
2079 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2080 BasicBlock *Dst = SI->getSuccessor(i);
2081 if (isOnlyReachableViaThisEdge(Parent, Dst, DT))
2082 Changed |= propagateEquality(SwitchCond, SI->getCaseValue(i), Dst);
2083 }
2084 return Changed;
2085 }
2086
2087 // Instructions with void type don't return a value, so there's
2088 // no point in trying to find redudancies in them.
2089 if (I->getType()->isVoidTy()) return false;
2090
2091 uint32_t NextNum = VN.getNextUnusedValueNumber();
2092 unsigned Num = VN.lookup_or_add(I);
2093
2094 // Allocations are always uniquely numbered, so we can save time and memory
2095 // by fast failing them.
2096 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) {
2097 addToLeaderTable(Num, I, I->getParent());
2098 return false;
2099 }
2100
2101 // If the number we were assigned was a brand new VN, then we don't
2102 // need to do a lookup to see if the number already exists
2103 // somewhere in the domtree: it can't!
2104 if (Num == NextNum) {
2105 addToLeaderTable(Num, I, I->getParent());
2106 return false;
2107 }
2108
2109 // Perform fast-path value-number based elimination of values inherited from
2110 // dominators.
2111 Value *repl = findLeader(I->getParent(), Num);
2112 if (repl == 0) {
2113 // Failure, just remember this instance for future use.
2114 addToLeaderTable(Num, I, I->getParent());
2115 return false;
2116 }
2117
2118 // Remove it!
2119 I->replaceAllUsesWith(repl);
2120 if (MD && repl->getType()->isPointerTy())
2121 MD->invalidateCachedPointerInfo(repl);
2122 markInstructionForDeletion(I);
2123 return true;
2124 }
2125
2126 /// runOnFunction - This is the main transformation entry point for a function.
runOnFunction(Function & F)2127 bool GVN::runOnFunction(Function& F) {
2128 if (!NoLoads)
2129 MD = &getAnalysis<MemoryDependenceAnalysis>();
2130 DT = &getAnalysis<DominatorTree>();
2131 TD = getAnalysisIfAvailable<TargetData>();
2132 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2133 VN.setMemDep(MD);
2134 VN.setDomTree(DT);
2135
2136 bool Changed = false;
2137 bool ShouldContinue = true;
2138
2139 // Merge unconditional branches, allowing PRE to catch more
2140 // optimization opportunities.
2141 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2142 BasicBlock *BB = FI++;
2143
2144 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2145 if (removedBlock) ++NumGVNBlocks;
2146
2147 Changed |= removedBlock;
2148 }
2149
2150 unsigned Iteration = 0;
2151 while (ShouldContinue) {
2152 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2153 ShouldContinue = iterateOnFunction(F);
2154 if (splitCriticalEdges())
2155 ShouldContinue = true;
2156 Changed |= ShouldContinue;
2157 ++Iteration;
2158 }
2159
2160 if (EnablePRE) {
2161 bool PREChanged = true;
2162 while (PREChanged) {
2163 PREChanged = performPRE(F);
2164 Changed |= PREChanged;
2165 }
2166 }
2167 // FIXME: Should perform GVN again after PRE does something. PRE can move
2168 // computations into blocks where they become fully redundant. Note that
2169 // we can't do this until PRE's critical edge splitting updates memdep.
2170 // Actually, when this happens, we should just fully integrate PRE into GVN.
2171
2172 cleanupGlobalSets();
2173
2174 return Changed;
2175 }
2176
2177
processBlock(BasicBlock * BB)2178 bool GVN::processBlock(BasicBlock *BB) {
2179 // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function
2180 // (and incrementing BI before processing an instruction).
2181 assert(InstrsToErase.empty() &&
2182 "We expect InstrsToErase to be empty across iterations");
2183 bool ChangedFunction = false;
2184
2185 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2186 BI != BE;) {
2187 ChangedFunction |= processInstruction(BI);
2188 if (InstrsToErase.empty()) {
2189 ++BI;
2190 continue;
2191 }
2192
2193 // If we need some instructions deleted, do it now.
2194 NumGVNInstr += InstrsToErase.size();
2195
2196 // Avoid iterator invalidation.
2197 bool AtStart = BI == BB->begin();
2198 if (!AtStart)
2199 --BI;
2200
2201 for (SmallVector<Instruction*, 4>::iterator I = InstrsToErase.begin(),
2202 E = InstrsToErase.end(); I != E; ++I) {
2203 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2204 if (MD) MD->removeInstruction(*I);
2205 (*I)->eraseFromParent();
2206 DEBUG(verifyRemoved(*I));
2207 }
2208 InstrsToErase.clear();
2209
2210 if (AtStart)
2211 BI = BB->begin();
2212 else
2213 ++BI;
2214 }
2215
2216 return ChangedFunction;
2217 }
2218
2219 /// performPRE - Perform a purely local form of PRE that looks for diamond
2220 /// control flow patterns and attempts to perform simple PRE at the join point.
performPRE(Function & F)2221 bool GVN::performPRE(Function &F) {
2222 bool Changed = false;
2223 DenseMap<BasicBlock*, Value*> predMap;
2224 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2225 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2226 BasicBlock *CurrentBlock = *DI;
2227
2228 // Nothing to PRE in the entry block.
2229 if (CurrentBlock == &F.getEntryBlock()) continue;
2230
2231 // Don't perform PRE on a landing pad.
2232 if (CurrentBlock->isLandingPad()) continue;
2233
2234 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2235 BE = CurrentBlock->end(); BI != BE; ) {
2236 Instruction *CurInst = BI++;
2237
2238 if (isa<AllocaInst>(CurInst) ||
2239 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2240 CurInst->getType()->isVoidTy() ||
2241 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2242 isa<DbgInfoIntrinsic>(CurInst))
2243 continue;
2244
2245 // We don't currently value number ANY inline asm calls.
2246 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2247 if (CallI->isInlineAsm())
2248 continue;
2249
2250 uint32_t ValNo = VN.lookup(CurInst);
2251
2252 // Look for the predecessors for PRE opportunities. We're
2253 // only trying to solve the basic diamond case, where
2254 // a value is computed in the successor and one predecessor,
2255 // but not the other. We also explicitly disallow cases
2256 // where the successor is its own predecessor, because they're
2257 // more complicated to get right.
2258 unsigned NumWith = 0;
2259 unsigned NumWithout = 0;
2260 BasicBlock *PREPred = 0;
2261 predMap.clear();
2262
2263 for (pred_iterator PI = pred_begin(CurrentBlock),
2264 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2265 BasicBlock *P = *PI;
2266 // We're not interested in PRE where the block is its
2267 // own predecessor, or in blocks with predecessors
2268 // that are not reachable.
2269 if (P == CurrentBlock) {
2270 NumWithout = 2;
2271 break;
2272 } else if (!DT->dominates(&F.getEntryBlock(), P)) {
2273 NumWithout = 2;
2274 break;
2275 }
2276
2277 Value* predV = findLeader(P, ValNo);
2278 if (predV == 0) {
2279 PREPred = P;
2280 ++NumWithout;
2281 } else if (predV == CurInst) {
2282 NumWithout = 2;
2283 } else {
2284 predMap[P] = predV;
2285 ++NumWith;
2286 }
2287 }
2288
2289 // Don't do PRE when it might increase code size, i.e. when
2290 // we would need to insert instructions in more than one pred.
2291 if (NumWithout != 1 || NumWith == 0)
2292 continue;
2293
2294 // Don't do PRE across indirect branch.
2295 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2296 continue;
2297
2298 // We can't do PRE safely on a critical edge, so instead we schedule
2299 // the edge to be split and perform the PRE the next time we iterate
2300 // on the function.
2301 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2302 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2303 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2304 continue;
2305 }
2306
2307 // Instantiate the expression in the predecessor that lacked it.
2308 // Because we are going top-down through the block, all value numbers
2309 // will be available in the predecessor by the time we need them. Any
2310 // that weren't originally present will have been instantiated earlier
2311 // in this loop.
2312 Instruction *PREInstr = CurInst->clone();
2313 bool success = true;
2314 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2315 Value *Op = PREInstr->getOperand(i);
2316 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2317 continue;
2318
2319 if (Value *V = findLeader(PREPred, VN.lookup(Op))) {
2320 PREInstr->setOperand(i, V);
2321 } else {
2322 success = false;
2323 break;
2324 }
2325 }
2326
2327 // Fail out if we encounter an operand that is not available in
2328 // the PRE predecessor. This is typically because of loads which
2329 // are not value numbered precisely.
2330 if (!success) {
2331 delete PREInstr;
2332 DEBUG(verifyRemoved(PREInstr));
2333 continue;
2334 }
2335
2336 PREInstr->insertBefore(PREPred->getTerminator());
2337 PREInstr->setName(CurInst->getName() + ".pre");
2338 PREInstr->setDebugLoc(CurInst->getDebugLoc());
2339 predMap[PREPred] = PREInstr;
2340 VN.add(PREInstr, ValNo);
2341 ++NumGVNPRE;
2342
2343 // Update the availability map to include the new instruction.
2344 addToLeaderTable(ValNo, PREInstr, PREPred);
2345
2346 // Create a PHI to make the value available in this block.
2347 pred_iterator PB = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock);
2348 PHINode* Phi = PHINode::Create(CurInst->getType(), std::distance(PB, PE),
2349 CurInst->getName() + ".pre-phi",
2350 CurrentBlock->begin());
2351 for (pred_iterator PI = PB; PI != PE; ++PI) {
2352 BasicBlock *P = *PI;
2353 Phi->addIncoming(predMap[P], P);
2354 }
2355
2356 VN.add(Phi, ValNo);
2357 addToLeaderTable(ValNo, Phi, CurrentBlock);
2358 Phi->setDebugLoc(CurInst->getDebugLoc());
2359 CurInst->replaceAllUsesWith(Phi);
2360 if (Phi->getType()->isPointerTy()) {
2361 // Because we have added a PHI-use of the pointer value, it has now
2362 // "escaped" from alias analysis' perspective. We need to inform
2363 // AA of this.
2364 for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee;
2365 ++ii) {
2366 unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
2367 VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj));
2368 }
2369
2370 if (MD)
2371 MD->invalidateCachedPointerInfo(Phi);
2372 }
2373 VN.erase(CurInst);
2374 removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
2375
2376 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2377 if (MD) MD->removeInstruction(CurInst);
2378 CurInst->eraseFromParent();
2379 DEBUG(verifyRemoved(CurInst));
2380 Changed = true;
2381 }
2382 }
2383
2384 if (splitCriticalEdges())
2385 Changed = true;
2386
2387 return Changed;
2388 }
2389
2390 /// splitCriticalEdges - Split critical edges found during the previous
2391 /// iteration that may enable further optimization.
splitCriticalEdges()2392 bool GVN::splitCriticalEdges() {
2393 if (toSplit.empty())
2394 return false;
2395 do {
2396 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2397 SplitCriticalEdge(Edge.first, Edge.second, this);
2398 } while (!toSplit.empty());
2399 if (MD) MD->invalidateCachedPredecessors();
2400 return true;
2401 }
2402
2403 /// iterateOnFunction - Executes one iteration of GVN
iterateOnFunction(Function & F)2404 bool GVN::iterateOnFunction(Function &F) {
2405 cleanupGlobalSets();
2406
2407 // Top-down walk of the dominator tree
2408 bool Changed = false;
2409 #if 0
2410 // Needed for value numbering with phi construction to work.
2411 ReversePostOrderTraversal<Function*> RPOT(&F);
2412 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2413 RE = RPOT.end(); RI != RE; ++RI)
2414 Changed |= processBlock(*RI);
2415 #else
2416 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2417 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2418 Changed |= processBlock(DI->getBlock());
2419 #endif
2420
2421 return Changed;
2422 }
2423
cleanupGlobalSets()2424 void GVN::cleanupGlobalSets() {
2425 VN.clear();
2426 LeaderTable.clear();
2427 TableAllocator.Reset();
2428 }
2429
2430 /// verifyRemoved - Verify that the specified instruction does not occur in our
2431 /// internal data structures.
verifyRemoved(const Instruction * Inst) const2432 void GVN::verifyRemoved(const Instruction *Inst) const {
2433 VN.verifyRemoved(Inst);
2434
2435 // Walk through the value number scope to make sure the instruction isn't
2436 // ferreted away in it.
2437 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator
2438 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) {
2439 const LeaderTableEntry *Node = &I->second;
2440 assert(Node->Val != Inst && "Inst still in value numbering scope!");
2441
2442 while (Node->Next) {
2443 Node = Node->Next;
2444 assert(Node->Val != Inst && "Inst still in value numbering scope!");
2445 }
2446 }
2447 }
2448