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 #include "llvm/Transforms/Scalar.h"
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/ADT/DepthFirstIterator.h"
21 #include "llvm/ADT/Hashing.h"
22 #include "llvm/ADT/MapVector.h"
23 #include "llvm/ADT/SetVector.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/ADT/Statistic.h"
26 #include "llvm/Analysis/AliasAnalysis.h"
27 #include "llvm/Analysis/CFG.h"
28 #include "llvm/Analysis/ConstantFolding.h"
29 #include "llvm/Analysis/InstructionSimplify.h"
30 #include "llvm/Analysis/Loads.h"
31 #include "llvm/Analysis/MemoryBuiltins.h"
32 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
33 #include "llvm/Analysis/PHITransAddr.h"
34 #include "llvm/Analysis/ValueTracking.h"
35 #include "llvm/IR/DataLayout.h"
36 #include "llvm/IR/Dominators.h"
37 #include "llvm/IR/GlobalVariable.h"
38 #include "llvm/IR/IRBuilder.h"
39 #include "llvm/IR/IntrinsicInst.h"
40 #include "llvm/IR/LLVMContext.h"
41 #include "llvm/IR/Metadata.h"
42 #include "llvm/IR/PatternMatch.h"
43 #include "llvm/Support/Allocator.h"
44 #include "llvm/Support/CommandLine.h"
45 #include "llvm/Support/Debug.h"
46 #include "llvm/Target/TargetLibraryInfo.h"
47 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
48 #include "llvm/Transforms/Utils/SSAUpdater.h"
49 #include <vector>
50 using namespace llvm;
51 using namespace PatternMatch;
52
53 #define DEBUG_TYPE "gvn"
54
55 STATISTIC(NumGVNInstr, "Number of instructions deleted");
56 STATISTIC(NumGVNLoad, "Number of loads deleted");
57 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
58 STATISTIC(NumGVNBlocks, "Number of blocks merged");
59 STATISTIC(NumGVNSimpl, "Number of instructions simplified");
60 STATISTIC(NumGVNEqProp, "Number of equalities propagated");
61 STATISTIC(NumPRELoad, "Number of loads PRE'd");
62
63 static cl::opt<bool> EnablePRE("enable-pre",
64 cl::init(true), cl::Hidden);
65 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
66
67 // Maximum allowed recursion depth.
68 static cl::opt<uint32_t>
69 MaxRecurseDepth("max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore,
70 cl::desc("Max recurse depth (default = 1000)"));
71
72 //===----------------------------------------------------------------------===//
73 // ValueTable Class
74 //===----------------------------------------------------------------------===//
75
76 /// This class holds the mapping between values and value numbers. It is used
77 /// as an efficient mechanism to determine the expression-wise equivalence of
78 /// two values.
79 namespace {
80 struct Expression {
81 uint32_t opcode;
82 Type *type;
83 SmallVector<uint32_t, 4> varargs;
84
Expression__anon64de0b970111::Expression85 Expression(uint32_t o = ~2U) : opcode(o) { }
86
operator ==__anon64de0b970111::Expression87 bool operator==(const Expression &other) const {
88 if (opcode != other.opcode)
89 return false;
90 if (opcode == ~0U || opcode == ~1U)
91 return true;
92 if (type != other.type)
93 return false;
94 if (varargs != other.varargs)
95 return false;
96 return true;
97 }
98
hash_value(const Expression & Value)99 friend hash_code hash_value(const Expression &Value) {
100 return hash_combine(Value.opcode, Value.type,
101 hash_combine_range(Value.varargs.begin(),
102 Value.varargs.end()));
103 }
104 };
105
106 class ValueTable {
107 DenseMap<Value*, uint32_t> valueNumbering;
108 DenseMap<Expression, uint32_t> expressionNumbering;
109 AliasAnalysis *AA;
110 MemoryDependenceAnalysis *MD;
111 DominatorTree *DT;
112
113 uint32_t nextValueNumber;
114
115 Expression create_expression(Instruction* I);
116 Expression create_cmp_expression(unsigned Opcode,
117 CmpInst::Predicate Predicate,
118 Value *LHS, Value *RHS);
119 Expression create_extractvalue_expression(ExtractValueInst* EI);
120 uint32_t lookup_or_add_call(CallInst* C);
121 public:
ValueTable()122 ValueTable() : nextValueNumber(1) { }
123 uint32_t lookup_or_add(Value *V);
124 uint32_t lookup(Value *V) const;
125 uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred,
126 Value *LHS, Value *RHS);
127 void add(Value *V, uint32_t num);
128 void clear();
129 void erase(Value *v);
setAliasAnalysis(AliasAnalysis * A)130 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
getAliasAnalysis() const131 AliasAnalysis *getAliasAnalysis() const { return AA; }
setMemDep(MemoryDependenceAnalysis * M)132 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
setDomTree(DominatorTree * D)133 void setDomTree(DominatorTree* D) { DT = D; }
getNextUnusedValueNumber()134 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
135 void verifyRemoved(const Value *) const;
136 };
137 }
138
139 namespace llvm {
140 template <> struct DenseMapInfo<Expression> {
getEmptyKeyllvm::DenseMapInfo141 static inline Expression getEmptyKey() {
142 return ~0U;
143 }
144
getTombstoneKeyllvm::DenseMapInfo145 static inline Expression getTombstoneKey() {
146 return ~1U;
147 }
148
getHashValuellvm::DenseMapInfo149 static unsigned getHashValue(const Expression e) {
150 using llvm::hash_value;
151 return static_cast<unsigned>(hash_value(e));
152 }
isEqualllvm::DenseMapInfo153 static bool isEqual(const Expression &LHS, const Expression &RHS) {
154 return LHS == RHS;
155 }
156 };
157
158 }
159
160 //===----------------------------------------------------------------------===//
161 // ValueTable Internal Functions
162 //===----------------------------------------------------------------------===//
163
create_expression(Instruction * I)164 Expression ValueTable::create_expression(Instruction *I) {
165 Expression e;
166 e.type = I->getType();
167 e.opcode = I->getOpcode();
168 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
169 OI != OE; ++OI)
170 e.varargs.push_back(lookup_or_add(*OI));
171 if (I->isCommutative()) {
172 // Ensure that commutative instructions that only differ by a permutation
173 // of their operands get the same value number by sorting the operand value
174 // numbers. Since all commutative instructions have two operands it is more
175 // efficient to sort by hand rather than using, say, std::sort.
176 assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
177 if (e.varargs[0] > e.varargs[1])
178 std::swap(e.varargs[0], e.varargs[1]);
179 }
180
181 if (CmpInst *C = dyn_cast<CmpInst>(I)) {
182 // Sort the operand value numbers so x<y and y>x get the same value number.
183 CmpInst::Predicate Predicate = C->getPredicate();
184 if (e.varargs[0] > e.varargs[1]) {
185 std::swap(e.varargs[0], e.varargs[1]);
186 Predicate = CmpInst::getSwappedPredicate(Predicate);
187 }
188 e.opcode = (C->getOpcode() << 8) | Predicate;
189 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) {
190 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
191 II != IE; ++II)
192 e.varargs.push_back(*II);
193 }
194
195 return e;
196 }
197
create_cmp_expression(unsigned Opcode,CmpInst::Predicate Predicate,Value * LHS,Value * RHS)198 Expression ValueTable::create_cmp_expression(unsigned Opcode,
199 CmpInst::Predicate Predicate,
200 Value *LHS, Value *RHS) {
201 assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
202 "Not a comparison!");
203 Expression e;
204 e.type = CmpInst::makeCmpResultType(LHS->getType());
205 e.varargs.push_back(lookup_or_add(LHS));
206 e.varargs.push_back(lookup_or_add(RHS));
207
208 // Sort the operand value numbers so x<y and y>x get the same value number.
209 if (e.varargs[0] > e.varargs[1]) {
210 std::swap(e.varargs[0], e.varargs[1]);
211 Predicate = CmpInst::getSwappedPredicate(Predicate);
212 }
213 e.opcode = (Opcode << 8) | Predicate;
214 return e;
215 }
216
create_extractvalue_expression(ExtractValueInst * EI)217 Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) {
218 assert(EI && "Not an ExtractValueInst?");
219 Expression e;
220 e.type = EI->getType();
221 e.opcode = 0;
222
223 IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
224 if (I != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) {
225 // EI might be an extract from one of our recognised intrinsics. If it
226 // is we'll synthesize a semantically equivalent expression instead on
227 // an extract value expression.
228 switch (I->getIntrinsicID()) {
229 case Intrinsic::sadd_with_overflow:
230 case Intrinsic::uadd_with_overflow:
231 e.opcode = Instruction::Add;
232 break;
233 case Intrinsic::ssub_with_overflow:
234 case Intrinsic::usub_with_overflow:
235 e.opcode = Instruction::Sub;
236 break;
237 case Intrinsic::smul_with_overflow:
238 case Intrinsic::umul_with_overflow:
239 e.opcode = Instruction::Mul;
240 break;
241 default:
242 break;
243 }
244
245 if (e.opcode != 0) {
246 // Intrinsic recognized. Grab its args to finish building the expression.
247 assert(I->getNumArgOperands() == 2 &&
248 "Expect two args for recognised intrinsics.");
249 e.varargs.push_back(lookup_or_add(I->getArgOperand(0)));
250 e.varargs.push_back(lookup_or_add(I->getArgOperand(1)));
251 return e;
252 }
253 }
254
255 // Not a recognised intrinsic. Fall back to producing an extract value
256 // expression.
257 e.opcode = EI->getOpcode();
258 for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end();
259 OI != OE; ++OI)
260 e.varargs.push_back(lookup_or_add(*OI));
261
262 for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end();
263 II != IE; ++II)
264 e.varargs.push_back(*II);
265
266 return e;
267 }
268
269 //===----------------------------------------------------------------------===//
270 // ValueTable External Functions
271 //===----------------------------------------------------------------------===//
272
273 /// add - Insert a value into the table with a specified value number.
add(Value * V,uint32_t num)274 void ValueTable::add(Value *V, uint32_t num) {
275 valueNumbering.insert(std::make_pair(V, num));
276 }
277
lookup_or_add_call(CallInst * C)278 uint32_t ValueTable::lookup_or_add_call(CallInst *C) {
279 if (AA->doesNotAccessMemory(C)) {
280 Expression exp = create_expression(C);
281 uint32_t &e = expressionNumbering[exp];
282 if (!e) e = nextValueNumber++;
283 valueNumbering[C] = e;
284 return e;
285 } else if (AA->onlyReadsMemory(C)) {
286 Expression exp = create_expression(C);
287 uint32_t &e = expressionNumbering[exp];
288 if (!e) {
289 e = nextValueNumber++;
290 valueNumbering[C] = e;
291 return e;
292 }
293 if (!MD) {
294 e = nextValueNumber++;
295 valueNumbering[C] = e;
296 return e;
297 }
298
299 MemDepResult local_dep = MD->getDependency(C);
300
301 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
302 valueNumbering[C] = nextValueNumber;
303 return nextValueNumber++;
304 }
305
306 if (local_dep.isDef()) {
307 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
308
309 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
310 valueNumbering[C] = nextValueNumber;
311 return nextValueNumber++;
312 }
313
314 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
315 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
316 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i));
317 if (c_vn != cd_vn) {
318 valueNumbering[C] = nextValueNumber;
319 return nextValueNumber++;
320 }
321 }
322
323 uint32_t v = lookup_or_add(local_cdep);
324 valueNumbering[C] = v;
325 return v;
326 }
327
328 // Non-local case.
329 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
330 MD->getNonLocalCallDependency(CallSite(C));
331 // FIXME: Move the checking logic to MemDep!
332 CallInst* cdep = nullptr;
333
334 // Check to see if we have a single dominating call instruction that is
335 // identical to C.
336 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
337 const NonLocalDepEntry *I = &deps[i];
338 if (I->getResult().isNonLocal())
339 continue;
340
341 // We don't handle non-definitions. If we already have a call, reject
342 // instruction dependencies.
343 if (!I->getResult().isDef() || cdep != nullptr) {
344 cdep = nullptr;
345 break;
346 }
347
348 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
349 // FIXME: All duplicated with non-local case.
350 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
351 cdep = NonLocalDepCall;
352 continue;
353 }
354
355 cdep = nullptr;
356 break;
357 }
358
359 if (!cdep) {
360 valueNumbering[C] = nextValueNumber;
361 return nextValueNumber++;
362 }
363
364 if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
365 valueNumbering[C] = nextValueNumber;
366 return nextValueNumber++;
367 }
368 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
369 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
370 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i));
371 if (c_vn != cd_vn) {
372 valueNumbering[C] = nextValueNumber;
373 return nextValueNumber++;
374 }
375 }
376
377 uint32_t v = lookup_or_add(cdep);
378 valueNumbering[C] = v;
379 return v;
380
381 } else {
382 valueNumbering[C] = nextValueNumber;
383 return nextValueNumber++;
384 }
385 }
386
387 /// lookup_or_add - Returns the value number for the specified value, assigning
388 /// it a new number if it did not have one before.
lookup_or_add(Value * V)389 uint32_t ValueTable::lookup_or_add(Value *V) {
390 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
391 if (VI != valueNumbering.end())
392 return VI->second;
393
394 if (!isa<Instruction>(V)) {
395 valueNumbering[V] = nextValueNumber;
396 return nextValueNumber++;
397 }
398
399 Instruction* I = cast<Instruction>(V);
400 Expression exp;
401 switch (I->getOpcode()) {
402 case Instruction::Call:
403 return lookup_or_add_call(cast<CallInst>(I));
404 case Instruction::Add:
405 case Instruction::FAdd:
406 case Instruction::Sub:
407 case Instruction::FSub:
408 case Instruction::Mul:
409 case Instruction::FMul:
410 case Instruction::UDiv:
411 case Instruction::SDiv:
412 case Instruction::FDiv:
413 case Instruction::URem:
414 case Instruction::SRem:
415 case Instruction::FRem:
416 case Instruction::Shl:
417 case Instruction::LShr:
418 case Instruction::AShr:
419 case Instruction::And:
420 case Instruction::Or:
421 case Instruction::Xor:
422 case Instruction::ICmp:
423 case Instruction::FCmp:
424 case Instruction::Trunc:
425 case Instruction::ZExt:
426 case Instruction::SExt:
427 case Instruction::FPToUI:
428 case Instruction::FPToSI:
429 case Instruction::UIToFP:
430 case Instruction::SIToFP:
431 case Instruction::FPTrunc:
432 case Instruction::FPExt:
433 case Instruction::PtrToInt:
434 case Instruction::IntToPtr:
435 case Instruction::BitCast:
436 case Instruction::Select:
437 case Instruction::ExtractElement:
438 case Instruction::InsertElement:
439 case Instruction::ShuffleVector:
440 case Instruction::InsertValue:
441 case Instruction::GetElementPtr:
442 exp = create_expression(I);
443 break;
444 case Instruction::ExtractValue:
445 exp = create_extractvalue_expression(cast<ExtractValueInst>(I));
446 break;
447 default:
448 valueNumbering[V] = nextValueNumber;
449 return nextValueNumber++;
450 }
451
452 uint32_t& e = expressionNumbering[exp];
453 if (!e) e = nextValueNumber++;
454 valueNumbering[V] = e;
455 return e;
456 }
457
458 /// lookup - Returns the value number of the specified value. Fails if
459 /// the value has not yet been numbered.
lookup(Value * V) const460 uint32_t ValueTable::lookup(Value *V) const {
461 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
462 assert(VI != valueNumbering.end() && "Value not numbered?");
463 return VI->second;
464 }
465
466 /// lookup_or_add_cmp - Returns the value number of the given comparison,
467 /// assigning it a new number if it did not have one before. Useful when
468 /// we deduced the result of a comparison, but don't immediately have an
469 /// instruction realizing that comparison to hand.
lookup_or_add_cmp(unsigned Opcode,CmpInst::Predicate Predicate,Value * LHS,Value * RHS)470 uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode,
471 CmpInst::Predicate Predicate,
472 Value *LHS, Value *RHS) {
473 Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS);
474 uint32_t& e = expressionNumbering[exp];
475 if (!e) e = nextValueNumber++;
476 return e;
477 }
478
479 /// clear - Remove all entries from the ValueTable.
clear()480 void ValueTable::clear() {
481 valueNumbering.clear();
482 expressionNumbering.clear();
483 nextValueNumber = 1;
484 }
485
486 /// erase - Remove a value from the value numbering.
erase(Value * V)487 void ValueTable::erase(Value *V) {
488 valueNumbering.erase(V);
489 }
490
491 /// verifyRemoved - Verify that the value is removed from all internal data
492 /// structures.
verifyRemoved(const Value * V) const493 void ValueTable::verifyRemoved(const Value *V) const {
494 for (DenseMap<Value*, uint32_t>::const_iterator
495 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
496 assert(I->first != V && "Inst still occurs in value numbering map!");
497 }
498 }
499
500 //===----------------------------------------------------------------------===//
501 // GVN Pass
502 //===----------------------------------------------------------------------===//
503
504 namespace {
505 class GVN;
506 struct AvailableValueInBlock {
507 /// BB - The basic block in question.
508 BasicBlock *BB;
509 enum ValType {
510 SimpleVal, // A simple offsetted value that is accessed.
511 LoadVal, // A value produced by a load.
512 MemIntrin, // A memory intrinsic which is loaded from.
513 UndefVal // A UndefValue representing a value from dead block (which
514 // is not yet physically removed from the CFG).
515 };
516
517 /// V - The value that is live out of the block.
518 PointerIntPair<Value *, 2, ValType> Val;
519
520 /// Offset - The byte offset in Val that is interesting for the load query.
521 unsigned Offset;
522
get__anon64de0b970211::AvailableValueInBlock523 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
524 unsigned Offset = 0) {
525 AvailableValueInBlock Res;
526 Res.BB = BB;
527 Res.Val.setPointer(V);
528 Res.Val.setInt(SimpleVal);
529 Res.Offset = Offset;
530 return Res;
531 }
532
getMI__anon64de0b970211::AvailableValueInBlock533 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
534 unsigned Offset = 0) {
535 AvailableValueInBlock Res;
536 Res.BB = BB;
537 Res.Val.setPointer(MI);
538 Res.Val.setInt(MemIntrin);
539 Res.Offset = Offset;
540 return Res;
541 }
542
getLoad__anon64de0b970211::AvailableValueInBlock543 static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI,
544 unsigned Offset = 0) {
545 AvailableValueInBlock Res;
546 Res.BB = BB;
547 Res.Val.setPointer(LI);
548 Res.Val.setInt(LoadVal);
549 Res.Offset = Offset;
550 return Res;
551 }
552
getUndef__anon64de0b970211::AvailableValueInBlock553 static AvailableValueInBlock getUndef(BasicBlock *BB) {
554 AvailableValueInBlock Res;
555 Res.BB = BB;
556 Res.Val.setPointer(nullptr);
557 Res.Val.setInt(UndefVal);
558 Res.Offset = 0;
559 return Res;
560 }
561
isSimpleValue__anon64de0b970211::AvailableValueInBlock562 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
isCoercedLoadValue__anon64de0b970211::AvailableValueInBlock563 bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; }
isMemIntrinValue__anon64de0b970211::AvailableValueInBlock564 bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; }
isUndefValue__anon64de0b970211::AvailableValueInBlock565 bool isUndefValue() const { return Val.getInt() == UndefVal; }
566
getSimpleValue__anon64de0b970211::AvailableValueInBlock567 Value *getSimpleValue() const {
568 assert(isSimpleValue() && "Wrong accessor");
569 return Val.getPointer();
570 }
571
getCoercedLoadValue__anon64de0b970211::AvailableValueInBlock572 LoadInst *getCoercedLoadValue() const {
573 assert(isCoercedLoadValue() && "Wrong accessor");
574 return cast<LoadInst>(Val.getPointer());
575 }
576
getMemIntrinValue__anon64de0b970211::AvailableValueInBlock577 MemIntrinsic *getMemIntrinValue() const {
578 assert(isMemIntrinValue() && "Wrong accessor");
579 return cast<MemIntrinsic>(Val.getPointer());
580 }
581
582 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
583 /// defined here to the specified type. This handles various coercion cases.
584 Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const;
585 };
586
587 class GVN : public FunctionPass {
588 bool NoLoads;
589 MemoryDependenceAnalysis *MD;
590 DominatorTree *DT;
591 const DataLayout *DL;
592 const TargetLibraryInfo *TLI;
593 SetVector<BasicBlock *> DeadBlocks;
594
595 ValueTable VN;
596
597 /// LeaderTable - A mapping from value numbers to lists of Value*'s that
598 /// have that value number. Use findLeader to query it.
599 struct LeaderTableEntry {
600 Value *Val;
601 const BasicBlock *BB;
602 LeaderTableEntry *Next;
603 };
604 DenseMap<uint32_t, LeaderTableEntry> LeaderTable;
605 BumpPtrAllocator TableAllocator;
606
607 SmallVector<Instruction*, 8> InstrsToErase;
608
609 typedef SmallVector<NonLocalDepResult, 64> LoadDepVect;
610 typedef SmallVector<AvailableValueInBlock, 64> AvailValInBlkVect;
611 typedef SmallVector<BasicBlock*, 64> UnavailBlkVect;
612
613 public:
614 static char ID; // Pass identification, replacement for typeid
GVN(bool noloads=false)615 explicit GVN(bool noloads = false)
616 : FunctionPass(ID), NoLoads(noloads), MD(nullptr) {
617 initializeGVNPass(*PassRegistry::getPassRegistry());
618 }
619
620 bool runOnFunction(Function &F) override;
621
622 /// markInstructionForDeletion - This removes the specified instruction from
623 /// our various maps and marks it for deletion.
markInstructionForDeletion(Instruction * I)624 void markInstructionForDeletion(Instruction *I) {
625 VN.erase(I);
626 InstrsToErase.push_back(I);
627 }
628
getDataLayout() const629 const DataLayout *getDataLayout() const { return DL; }
getDominatorTree() const630 DominatorTree &getDominatorTree() const { return *DT; }
getAliasAnalysis() const631 AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); }
getMemDep() const632 MemoryDependenceAnalysis &getMemDep() const { return *MD; }
633 private:
634 /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for
635 /// its value number.
addToLeaderTable(uint32_t N,Value * V,const BasicBlock * BB)636 void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) {
637 LeaderTableEntry &Curr = LeaderTable[N];
638 if (!Curr.Val) {
639 Curr.Val = V;
640 Curr.BB = BB;
641 return;
642 }
643
644 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>();
645 Node->Val = V;
646 Node->BB = BB;
647 Node->Next = Curr.Next;
648 Curr.Next = Node;
649 }
650
651 /// removeFromLeaderTable - Scan the list of values corresponding to a given
652 /// value number, and remove the given instruction if encountered.
removeFromLeaderTable(uint32_t N,Instruction * I,BasicBlock * BB)653 void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) {
654 LeaderTableEntry* Prev = nullptr;
655 LeaderTableEntry* Curr = &LeaderTable[N];
656
657 while (Curr->Val != I || Curr->BB != BB) {
658 Prev = Curr;
659 Curr = Curr->Next;
660 }
661
662 if (Prev) {
663 Prev->Next = Curr->Next;
664 } else {
665 if (!Curr->Next) {
666 Curr->Val = nullptr;
667 Curr->BB = nullptr;
668 } else {
669 LeaderTableEntry* Next = Curr->Next;
670 Curr->Val = Next->Val;
671 Curr->BB = Next->BB;
672 Curr->Next = Next->Next;
673 }
674 }
675 }
676
677 // List of critical edges to be split between iterations.
678 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
679
680 // This transformation requires dominator postdominator info
getAnalysisUsage(AnalysisUsage & AU) const681 void getAnalysisUsage(AnalysisUsage &AU) const override {
682 AU.addRequired<DominatorTreeWrapperPass>();
683 AU.addRequired<TargetLibraryInfo>();
684 if (!NoLoads)
685 AU.addRequired<MemoryDependenceAnalysis>();
686 AU.addRequired<AliasAnalysis>();
687
688 AU.addPreserved<DominatorTreeWrapperPass>();
689 AU.addPreserved<AliasAnalysis>();
690 }
691
692
693 // Helper fuctions of redundant load elimination
694 bool processLoad(LoadInst *L);
695 bool processNonLocalLoad(LoadInst *L);
696 void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
697 AvailValInBlkVect &ValuesPerBlock,
698 UnavailBlkVect &UnavailableBlocks);
699 bool PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
700 UnavailBlkVect &UnavailableBlocks);
701
702 // Other helper routines
703 bool processInstruction(Instruction *I);
704 bool processBlock(BasicBlock *BB);
705 void dump(DenseMap<uint32_t, Value*> &d);
706 bool iterateOnFunction(Function &F);
707 bool performPRE(Function &F);
708 Value *findLeader(const BasicBlock *BB, uint32_t num);
709 void cleanupGlobalSets();
710 void verifyRemoved(const Instruction *I) const;
711 bool splitCriticalEdges();
712 BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
713 unsigned replaceAllDominatedUsesWith(Value *From, Value *To,
714 const BasicBlockEdge &Root);
715 bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root);
716 bool processFoldableCondBr(BranchInst *BI);
717 void addDeadBlock(BasicBlock *BB);
718 void assignValNumForDeadCode();
719 };
720
721 char GVN::ID = 0;
722 }
723
724 // createGVNPass - The public interface to this file...
createGVNPass(bool NoLoads)725 FunctionPass *llvm::createGVNPass(bool NoLoads) {
726 return new GVN(NoLoads);
727 }
728
729 INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)730 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
731 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
732 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
733 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
734 INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false)
735
736 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
737 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
738 errs() << "{\n";
739 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
740 E = d.end(); I != E; ++I) {
741 errs() << I->first << "\n";
742 I->second->dump();
743 }
744 errs() << "}\n";
745 }
746 #endif
747
748 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
749 /// we're analyzing is fully available in the specified block. As we go, keep
750 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
751 /// map is actually a tri-state map with the following values:
752 /// 0) we know the block *is not* fully available.
753 /// 1) we know the block *is* fully available.
754 /// 2) we do not know whether the block is fully available or not, but we are
755 /// currently speculating that it will be.
756 /// 3) we are speculating for this block and have used that to speculate for
757 /// other blocks.
IsValueFullyAvailableInBlock(BasicBlock * BB,DenseMap<BasicBlock *,char> & FullyAvailableBlocks,uint32_t RecurseDepth)758 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
759 DenseMap<BasicBlock*, char> &FullyAvailableBlocks,
760 uint32_t RecurseDepth) {
761 if (RecurseDepth > MaxRecurseDepth)
762 return false;
763
764 // Optimistically assume that the block is fully available and check to see
765 // if we already know about this block in one lookup.
766 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
767 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
768
769 // If the entry already existed for this block, return the precomputed value.
770 if (!IV.second) {
771 // If this is a speculative "available" value, mark it as being used for
772 // speculation of other blocks.
773 if (IV.first->second == 2)
774 IV.first->second = 3;
775 return IV.first->second != 0;
776 }
777
778 // Otherwise, see if it is fully available in all predecessors.
779 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
780
781 // If this block has no predecessors, it isn't live-in here.
782 if (PI == PE)
783 goto SpeculationFailure;
784
785 for (; PI != PE; ++PI)
786 // If the value isn't fully available in one of our predecessors, then it
787 // isn't fully available in this block either. Undo our previous
788 // optimistic assumption and bail out.
789 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1))
790 goto SpeculationFailure;
791
792 return true;
793
794 // SpeculationFailure - If we get here, we found out that this is not, after
795 // all, a fully-available block. We have a problem if we speculated on this and
796 // used the speculation to mark other blocks as available.
797 SpeculationFailure:
798 char &BBVal = FullyAvailableBlocks[BB];
799
800 // If we didn't speculate on this, just return with it set to false.
801 if (BBVal == 2) {
802 BBVal = 0;
803 return false;
804 }
805
806 // If we did speculate on this value, we could have blocks set to 1 that are
807 // incorrect. Walk the (transitive) successors of this block and mark them as
808 // 0 if set to one.
809 SmallVector<BasicBlock*, 32> BBWorklist;
810 BBWorklist.push_back(BB);
811
812 do {
813 BasicBlock *Entry = BBWorklist.pop_back_val();
814 // Note that this sets blocks to 0 (unavailable) if they happen to not
815 // already be in FullyAvailableBlocks. This is safe.
816 char &EntryVal = FullyAvailableBlocks[Entry];
817 if (EntryVal == 0) continue; // Already unavailable.
818
819 // Mark as unavailable.
820 EntryVal = 0;
821
822 BBWorklist.append(succ_begin(Entry), succ_end(Entry));
823 } while (!BBWorklist.empty());
824
825 return false;
826 }
827
828
829 /// CanCoerceMustAliasedValueToLoad - Return true if
830 /// CoerceAvailableValueToLoadType will succeed.
CanCoerceMustAliasedValueToLoad(Value * StoredVal,Type * LoadTy,const DataLayout & DL)831 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
832 Type *LoadTy,
833 const DataLayout &DL) {
834 // If the loaded or stored value is an first class array or struct, don't try
835 // to transform them. We need to be able to bitcast to integer.
836 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
837 StoredVal->getType()->isStructTy() ||
838 StoredVal->getType()->isArrayTy())
839 return false;
840
841 // The store has to be at least as big as the load.
842 if (DL.getTypeSizeInBits(StoredVal->getType()) <
843 DL.getTypeSizeInBits(LoadTy))
844 return false;
845
846 return true;
847 }
848
849 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
850 /// then a load from a must-aliased pointer of a different type, try to coerce
851 /// the stored value. LoadedTy is the type of the load we want to replace and
852 /// InsertPt is the place to insert new instructions.
853 ///
854 /// If we can't do it, return null.
CoerceAvailableValueToLoadType(Value * StoredVal,Type * LoadedTy,Instruction * InsertPt,const DataLayout & DL)855 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
856 Type *LoadedTy,
857 Instruction *InsertPt,
858 const DataLayout &DL) {
859 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, DL))
860 return nullptr;
861
862 // If this is already the right type, just return it.
863 Type *StoredValTy = StoredVal->getType();
864
865 uint64_t StoreSize = DL.getTypeSizeInBits(StoredValTy);
866 uint64_t LoadSize = DL.getTypeSizeInBits(LoadedTy);
867
868 // If the store and reload are the same size, we can always reuse it.
869 if (StoreSize == LoadSize) {
870 // Pointer to Pointer -> use bitcast.
871 if (StoredValTy->getScalarType()->isPointerTy() &&
872 LoadedTy->getScalarType()->isPointerTy())
873 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
874
875 // Convert source pointers to integers, which can be bitcast.
876 if (StoredValTy->getScalarType()->isPointerTy()) {
877 StoredValTy = DL.getIntPtrType(StoredValTy);
878 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
879 }
880
881 Type *TypeToCastTo = LoadedTy;
882 if (TypeToCastTo->getScalarType()->isPointerTy())
883 TypeToCastTo = DL.getIntPtrType(TypeToCastTo);
884
885 if (StoredValTy != TypeToCastTo)
886 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
887
888 // Cast to pointer if the load needs a pointer type.
889 if (LoadedTy->getScalarType()->isPointerTy())
890 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
891
892 return StoredVal;
893 }
894
895 // If the loaded value is smaller than the available value, then we can
896 // extract out a piece from it. If the available value is too small, then we
897 // can't do anything.
898 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
899
900 // Convert source pointers to integers, which can be manipulated.
901 if (StoredValTy->getScalarType()->isPointerTy()) {
902 StoredValTy = DL.getIntPtrType(StoredValTy);
903 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
904 }
905
906 // Convert vectors and fp to integer, which can be manipulated.
907 if (!StoredValTy->isIntegerTy()) {
908 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
909 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
910 }
911
912 // If this is a big-endian system, we need to shift the value down to the low
913 // bits so that a truncate will work.
914 if (DL.isBigEndian()) {
915 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
916 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
917 }
918
919 // Truncate the integer to the right size now.
920 Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
921 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
922
923 if (LoadedTy == NewIntTy)
924 return StoredVal;
925
926 // If the result is a pointer, inttoptr.
927 if (LoadedTy->getScalarType()->isPointerTy())
928 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
929
930 // Otherwise, bitcast.
931 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
932 }
933
934 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
935 /// memdep query of a load that ends up being a clobbering memory write (store,
936 /// memset, memcpy, memmove). This means that the write *may* provide bits used
937 /// by the load but we can't be sure because the pointers don't mustalias.
938 ///
939 /// Check this case to see if there is anything more we can do before we give
940 /// up. This returns -1 if we have to give up, or a byte number in the stored
941 /// value of the piece that feeds the load.
AnalyzeLoadFromClobberingWrite(Type * LoadTy,Value * LoadPtr,Value * WritePtr,uint64_t WriteSizeInBits,const DataLayout & DL)942 static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr,
943 Value *WritePtr,
944 uint64_t WriteSizeInBits,
945 const DataLayout &DL) {
946 // If the loaded or stored value is a first class array or struct, don't try
947 // to transform them. We need to be able to bitcast to integer.
948 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
949 return -1;
950
951 int64_t StoreOffset = 0, LoadOffset = 0;
952 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr,StoreOffset,&DL);
953 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, &DL);
954 if (StoreBase != LoadBase)
955 return -1;
956
957 // If the load and store are to the exact same address, they should have been
958 // a must alias. AA must have gotten confused.
959 // FIXME: Study to see if/when this happens. One case is forwarding a memset
960 // to a load from the base of the memset.
961 #if 0
962 if (LoadOffset == StoreOffset) {
963 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
964 << "Base = " << *StoreBase << "\n"
965 << "Store Ptr = " << *WritePtr << "\n"
966 << "Store Offs = " << StoreOffset << "\n"
967 << "Load Ptr = " << *LoadPtr << "\n";
968 abort();
969 }
970 #endif
971
972 // If the load and store don't overlap at all, the store doesn't provide
973 // anything to the load. In this case, they really don't alias at all, AA
974 // must have gotten confused.
975 uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy);
976
977 if ((WriteSizeInBits & 7) | (LoadSize & 7))
978 return -1;
979 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
980 LoadSize >>= 3;
981
982
983 bool isAAFailure = false;
984 if (StoreOffset < LoadOffset)
985 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
986 else
987 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
988
989 if (isAAFailure) {
990 #if 0
991 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
992 << "Base = " << *StoreBase << "\n"
993 << "Store Ptr = " << *WritePtr << "\n"
994 << "Store Offs = " << StoreOffset << "\n"
995 << "Load Ptr = " << *LoadPtr << "\n";
996 abort();
997 #endif
998 return -1;
999 }
1000
1001 // If the Load isn't completely contained within the stored bits, we don't
1002 // have all the bits to feed it. We could do something crazy in the future
1003 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1004 // valuable.
1005 if (StoreOffset > LoadOffset ||
1006 StoreOffset+StoreSize < LoadOffset+LoadSize)
1007 return -1;
1008
1009 // Okay, we can do this transformation. Return the number of bytes into the
1010 // store that the load is.
1011 return LoadOffset-StoreOffset;
1012 }
1013
1014 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1015 /// memdep query of a load that ends up being a clobbering store.
AnalyzeLoadFromClobberingStore(Type * LoadTy,Value * LoadPtr,StoreInst * DepSI,const DataLayout & DL)1016 static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr,
1017 StoreInst *DepSI,
1018 const DataLayout &DL) {
1019 // Cannot handle reading from store of first-class aggregate yet.
1020 if (DepSI->getValueOperand()->getType()->isStructTy() ||
1021 DepSI->getValueOperand()->getType()->isArrayTy())
1022 return -1;
1023
1024 Value *StorePtr = DepSI->getPointerOperand();
1025 uint64_t StoreSize =DL.getTypeSizeInBits(DepSI->getValueOperand()->getType());
1026 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1027 StorePtr, StoreSize, DL);
1028 }
1029
1030 /// AnalyzeLoadFromClobberingLoad - This function is called when we have a
1031 /// memdep query of a load that ends up being clobbered by another load. See if
1032 /// the other load can feed into the second load.
AnalyzeLoadFromClobberingLoad(Type * LoadTy,Value * LoadPtr,LoadInst * DepLI,const DataLayout & DL)1033 static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr,
1034 LoadInst *DepLI, const DataLayout &DL){
1035 // Cannot handle reading from store of first-class aggregate yet.
1036 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy())
1037 return -1;
1038
1039 Value *DepPtr = DepLI->getPointerOperand();
1040 uint64_t DepSize = DL.getTypeSizeInBits(DepLI->getType());
1041 int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, DL);
1042 if (R != -1) return R;
1043
1044 // If we have a load/load clobber an DepLI can be widened to cover this load,
1045 // then we should widen it!
1046 int64_t LoadOffs = 0;
1047 const Value *LoadBase =
1048 GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, &DL);
1049 unsigned LoadSize = DL.getTypeStoreSize(LoadTy);
1050
1051 unsigned Size = MemoryDependenceAnalysis::
1052 getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, DL);
1053 if (Size == 0) return -1;
1054
1055 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, DL);
1056 }
1057
1058
1059
AnalyzeLoadFromClobberingMemInst(Type * LoadTy,Value * LoadPtr,MemIntrinsic * MI,const DataLayout & DL)1060 static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
1061 MemIntrinsic *MI,
1062 const DataLayout &DL) {
1063 // If the mem operation is a non-constant size, we can't handle it.
1064 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1065 if (!SizeCst) return -1;
1066 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1067
1068 // If this is memset, we just need to see if the offset is valid in the size
1069 // of the memset..
1070 if (MI->getIntrinsicID() == Intrinsic::memset)
1071 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1072 MemSizeInBits, DL);
1073
1074 // If we have a memcpy/memmove, the only case we can handle is if this is a
1075 // copy from constant memory. In that case, we can read directly from the
1076 // constant memory.
1077 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1078
1079 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1080 if (!Src) return -1;
1081
1082 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &DL));
1083 if (!GV || !GV->isConstant()) return -1;
1084
1085 // See if the access is within the bounds of the transfer.
1086 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1087 MI->getDest(), MemSizeInBits, DL);
1088 if (Offset == -1)
1089 return Offset;
1090
1091 unsigned AS = Src->getType()->getPointerAddressSpace();
1092 // Otherwise, see if we can constant fold a load from the constant with the
1093 // offset applied as appropriate.
1094 Src = ConstantExpr::getBitCast(Src,
1095 Type::getInt8PtrTy(Src->getContext(), AS));
1096 Constant *OffsetCst =
1097 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1098 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst);
1099 Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
1100 if (ConstantFoldLoadFromConstPtr(Src, &DL))
1101 return Offset;
1102 return -1;
1103 }
1104
1105
1106 /// GetStoreValueForLoad - This function is called when we have a
1107 /// memdep query of a load that ends up being a clobbering store. This means
1108 /// that the store provides bits used by the load but we the pointers don't
1109 /// mustalias. Check this case to see if there is anything more we can do
1110 /// before we give up.
GetStoreValueForLoad(Value * SrcVal,unsigned Offset,Type * LoadTy,Instruction * InsertPt,const DataLayout & DL)1111 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1112 Type *LoadTy,
1113 Instruction *InsertPt, const DataLayout &DL){
1114 LLVMContext &Ctx = SrcVal->getType()->getContext();
1115
1116 uint64_t StoreSize = (DL.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1117 uint64_t LoadSize = (DL.getTypeSizeInBits(LoadTy) + 7) / 8;
1118
1119 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1120
1121 // Compute which bits of the stored value are being used by the load. Convert
1122 // to an integer type to start with.
1123 if (SrcVal->getType()->getScalarType()->isPointerTy())
1124 SrcVal = Builder.CreatePtrToInt(SrcVal,
1125 DL.getIntPtrType(SrcVal->getType()));
1126 if (!SrcVal->getType()->isIntegerTy())
1127 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8));
1128
1129 // Shift the bits to the least significant depending on endianness.
1130 unsigned ShiftAmt;
1131 if (DL.isLittleEndian())
1132 ShiftAmt = Offset*8;
1133 else
1134 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1135
1136 if (ShiftAmt)
1137 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt);
1138
1139 if (LoadSize != StoreSize)
1140 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8));
1141
1142 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, DL);
1143 }
1144
1145 /// GetLoadValueForLoad - This function is called when we have a
1146 /// memdep query of a load that ends up being a clobbering load. This means
1147 /// that the load *may* provide bits used by the load but we can't be sure
1148 /// because the pointers don't mustalias. Check this case to see if there is
1149 /// anything more we can do before we give up.
GetLoadValueForLoad(LoadInst * SrcVal,unsigned Offset,Type * LoadTy,Instruction * InsertPt,GVN & gvn)1150 static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset,
1151 Type *LoadTy, Instruction *InsertPt,
1152 GVN &gvn) {
1153 const DataLayout &DL = *gvn.getDataLayout();
1154 // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to
1155 // widen SrcVal out to a larger load.
1156 unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType());
1157 unsigned LoadSize = DL.getTypeStoreSize(LoadTy);
1158 if (Offset+LoadSize > SrcValSize) {
1159 assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!");
1160 assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load");
1161 // If we have a load/load clobber an DepLI can be widened to cover this
1162 // load, then we should widen it to the next power of 2 size big enough!
1163 unsigned NewLoadSize = Offset+LoadSize;
1164 if (!isPowerOf2_32(NewLoadSize))
1165 NewLoadSize = NextPowerOf2(NewLoadSize);
1166
1167 Value *PtrVal = SrcVal->getPointerOperand();
1168
1169 // Insert the new load after the old load. This ensures that subsequent
1170 // memdep queries will find the new load. We can't easily remove the old
1171 // load completely because it is already in the value numbering table.
1172 IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal));
1173 Type *DestPTy =
1174 IntegerType::get(LoadTy->getContext(), NewLoadSize*8);
1175 DestPTy = PointerType::get(DestPTy,
1176 PtrVal->getType()->getPointerAddressSpace());
1177 Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc());
1178 PtrVal = Builder.CreateBitCast(PtrVal, DestPTy);
1179 LoadInst *NewLoad = Builder.CreateLoad(PtrVal);
1180 NewLoad->takeName(SrcVal);
1181 NewLoad->setAlignment(SrcVal->getAlignment());
1182
1183 DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n");
1184 DEBUG(dbgs() << "TO: " << *NewLoad << "\n");
1185
1186 // Replace uses of the original load with the wider load. On a big endian
1187 // system, we need to shift down to get the relevant bits.
1188 Value *RV = NewLoad;
1189 if (DL.isBigEndian())
1190 RV = Builder.CreateLShr(RV,
1191 NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits());
1192 RV = Builder.CreateTrunc(RV, SrcVal->getType());
1193 SrcVal->replaceAllUsesWith(RV);
1194
1195 // We would like to use gvn.markInstructionForDeletion here, but we can't
1196 // because the load is already memoized into the leader map table that GVN
1197 // tracks. It is potentially possible to remove the load from the table,
1198 // but then there all of the operations based on it would need to be
1199 // rehashed. Just leave the dead load around.
1200 gvn.getMemDep().removeInstruction(SrcVal);
1201 SrcVal = NewLoad;
1202 }
1203
1204 return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, DL);
1205 }
1206
1207
1208 /// GetMemInstValueForLoad - This function is called when we have a
1209 /// memdep query of a load that ends up being a clobbering mem intrinsic.
GetMemInstValueForLoad(MemIntrinsic * SrcInst,unsigned Offset,Type * LoadTy,Instruction * InsertPt,const DataLayout & DL)1210 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1211 Type *LoadTy, Instruction *InsertPt,
1212 const DataLayout &DL){
1213 LLVMContext &Ctx = LoadTy->getContext();
1214 uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy)/8;
1215
1216 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1217
1218 // We know that this method is only called when the mem transfer fully
1219 // provides the bits for the load.
1220 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1221 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1222 // independently of what the offset is.
1223 Value *Val = MSI->getValue();
1224 if (LoadSize != 1)
1225 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1226
1227 Value *OneElt = Val;
1228
1229 // Splat the value out to the right number of bits.
1230 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1231 // If we can double the number of bytes set, do it.
1232 if (NumBytesSet*2 <= LoadSize) {
1233 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1234 Val = Builder.CreateOr(Val, ShVal);
1235 NumBytesSet <<= 1;
1236 continue;
1237 }
1238
1239 // Otherwise insert one byte at a time.
1240 Value *ShVal = Builder.CreateShl(Val, 1*8);
1241 Val = Builder.CreateOr(OneElt, ShVal);
1242 ++NumBytesSet;
1243 }
1244
1245 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, DL);
1246 }
1247
1248 // Otherwise, this is a memcpy/memmove from a constant global.
1249 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1250 Constant *Src = cast<Constant>(MTI->getSource());
1251 unsigned AS = Src->getType()->getPointerAddressSpace();
1252
1253 // Otherwise, see if we can constant fold a load from the constant with the
1254 // offset applied as appropriate.
1255 Src = ConstantExpr::getBitCast(Src,
1256 Type::getInt8PtrTy(Src->getContext(), AS));
1257 Constant *OffsetCst =
1258 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1259 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst);
1260 Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
1261 return ConstantFoldLoadFromConstPtr(Src, &DL);
1262 }
1263
1264
1265 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1266 /// construct SSA form, allowing us to eliminate LI. This returns the value
1267 /// that should be used at LI's definition site.
ConstructSSAForLoadSet(LoadInst * LI,SmallVectorImpl<AvailableValueInBlock> & ValuesPerBlock,GVN & gvn)1268 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1269 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1270 GVN &gvn) {
1271 // Check for the fully redundant, dominating load case. In this case, we can
1272 // just use the dominating value directly.
1273 if (ValuesPerBlock.size() == 1 &&
1274 gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB,
1275 LI->getParent())) {
1276 assert(!ValuesPerBlock[0].isUndefValue() && "Dead BB dominate this block");
1277 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn);
1278 }
1279
1280 // Otherwise, we have to construct SSA form.
1281 SmallVector<PHINode*, 8> NewPHIs;
1282 SSAUpdater SSAUpdate(&NewPHIs);
1283 SSAUpdate.Initialize(LI->getType(), LI->getName());
1284
1285 Type *LoadTy = LI->getType();
1286
1287 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1288 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1289 BasicBlock *BB = AV.BB;
1290
1291 if (SSAUpdate.HasValueForBlock(BB))
1292 continue;
1293
1294 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn));
1295 }
1296
1297 // Perform PHI construction.
1298 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1299
1300 // If new PHI nodes were created, notify alias analysis.
1301 if (V->getType()->getScalarType()->isPointerTy()) {
1302 AliasAnalysis *AA = gvn.getAliasAnalysis();
1303
1304 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1305 AA->copyValue(LI, NewPHIs[i]);
1306
1307 // Now that we've copied information to the new PHIs, scan through
1308 // them again and inform alias analysis that we've added potentially
1309 // escaping uses to any values that are operands to these PHIs.
1310 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) {
1311 PHINode *P = NewPHIs[i];
1312 for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) {
1313 unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
1314 AA->addEscapingUse(P->getOperandUse(jj));
1315 }
1316 }
1317 }
1318
1319 return V;
1320 }
1321
MaterializeAdjustedValue(Type * LoadTy,GVN & gvn) const1322 Value *AvailableValueInBlock::MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const {
1323 Value *Res;
1324 if (isSimpleValue()) {
1325 Res = getSimpleValue();
1326 if (Res->getType() != LoadTy) {
1327 const DataLayout *DL = gvn.getDataLayout();
1328 assert(DL && "Need target data to handle type mismatch case");
1329 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1330 *DL);
1331
1332 DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1333 << *getSimpleValue() << '\n'
1334 << *Res << '\n' << "\n\n\n");
1335 }
1336 } else if (isCoercedLoadValue()) {
1337 LoadInst *Load = getCoercedLoadValue();
1338 if (Load->getType() == LoadTy && Offset == 0) {
1339 Res = Load;
1340 } else {
1341 Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(),
1342 gvn);
1343
1344 DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " "
1345 << *getCoercedLoadValue() << '\n'
1346 << *Res << '\n' << "\n\n\n");
1347 }
1348 } else if (isMemIntrinValue()) {
1349 const DataLayout *DL = gvn.getDataLayout();
1350 assert(DL && "Need target data to handle type mismatch case");
1351 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1352 LoadTy, BB->getTerminator(), *DL);
1353 DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1354 << " " << *getMemIntrinValue() << '\n'
1355 << *Res << '\n' << "\n\n\n");
1356 } else {
1357 assert(isUndefValue() && "Should be UndefVal");
1358 DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";);
1359 return UndefValue::get(LoadTy);
1360 }
1361 return Res;
1362 }
1363
isLifetimeStart(const Instruction * Inst)1364 static bool isLifetimeStart(const Instruction *Inst) {
1365 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1366 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1367 return false;
1368 }
1369
AnalyzeLoadAvailability(LoadInst * LI,LoadDepVect & Deps,AvailValInBlkVect & ValuesPerBlock,UnavailBlkVect & UnavailableBlocks)1370 void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
1371 AvailValInBlkVect &ValuesPerBlock,
1372 UnavailBlkVect &UnavailableBlocks) {
1373
1374 // Filter out useless results (non-locals, etc). Keep track of the blocks
1375 // where we have a value available in repl, also keep track of whether we see
1376 // dependencies that produce an unknown value for the load (such as a call
1377 // that could potentially clobber the load).
1378 unsigned NumDeps = Deps.size();
1379 for (unsigned i = 0, e = NumDeps; i != e; ++i) {
1380 BasicBlock *DepBB = Deps[i].getBB();
1381 MemDepResult DepInfo = Deps[i].getResult();
1382
1383 if (DeadBlocks.count(DepBB)) {
1384 // Dead dependent mem-op disguise as a load evaluating the same value
1385 // as the load in question.
1386 ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB));
1387 continue;
1388 }
1389
1390 if (!DepInfo.isDef() && !DepInfo.isClobber()) {
1391 UnavailableBlocks.push_back(DepBB);
1392 continue;
1393 }
1394
1395 if (DepInfo.isClobber()) {
1396 // The address being loaded in this non-local block may not be the same as
1397 // the pointer operand of the load if PHI translation occurs. Make sure
1398 // to consider the right address.
1399 Value *Address = Deps[i].getAddress();
1400
1401 // If the dependence is to a store that writes to a superset of the bits
1402 // read by the load, we can extract the bits we need for the load from the
1403 // stored value.
1404 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1405 if (DL && Address) {
1406 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1407 DepSI, *DL);
1408 if (Offset != -1) {
1409 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1410 DepSI->getValueOperand(),
1411 Offset));
1412 continue;
1413 }
1414 }
1415 }
1416
1417 // Check to see if we have something like this:
1418 // load i32* P
1419 // load i8* (P+1)
1420 // if we have this, replace the later with an extraction from the former.
1421 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) {
1422 // If this is a clobber and L is the first instruction in its block, then
1423 // we have the first instruction in the entry block.
1424 if (DepLI != LI && Address && DL) {
1425 int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), Address,
1426 DepLI, *DL);
1427
1428 if (Offset != -1) {
1429 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI,
1430 Offset));
1431 continue;
1432 }
1433 }
1434 }
1435
1436 // If the clobbering value is a memset/memcpy/memmove, see if we can
1437 // forward a value on from it.
1438 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1439 if (DL && Address) {
1440 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1441 DepMI, *DL);
1442 if (Offset != -1) {
1443 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1444 Offset));
1445 continue;
1446 }
1447 }
1448 }
1449
1450 UnavailableBlocks.push_back(DepBB);
1451 continue;
1452 }
1453
1454 // DepInfo.isDef() here
1455
1456 Instruction *DepInst = DepInfo.getInst();
1457
1458 // Loading the allocation -> undef.
1459 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) ||
1460 // Loading immediately after lifetime begin -> undef.
1461 isLifetimeStart(DepInst)) {
1462 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1463 UndefValue::get(LI->getType())));
1464 continue;
1465 }
1466
1467 // Loading from calloc (which zero initializes memory) -> zero
1468 if (isCallocLikeFn(DepInst, TLI)) {
1469 ValuesPerBlock.push_back(AvailableValueInBlock::get(
1470 DepBB, Constant::getNullValue(LI->getType())));
1471 continue;
1472 }
1473
1474 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1475 // Reject loads and stores that are to the same address but are of
1476 // different types if we have to.
1477 if (S->getValueOperand()->getType() != LI->getType()) {
1478 // If the stored value is larger or equal to the loaded value, we can
1479 // reuse it.
1480 if (!DL || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(),
1481 LI->getType(), *DL)) {
1482 UnavailableBlocks.push_back(DepBB);
1483 continue;
1484 }
1485 }
1486
1487 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1488 S->getValueOperand()));
1489 continue;
1490 }
1491
1492 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1493 // If the types mismatch and we can't handle it, reject reuse of the load.
1494 if (LD->getType() != LI->getType()) {
1495 // If the stored value is larger or equal to the loaded value, we can
1496 // reuse it.
1497 if (!DL || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*DL)) {
1498 UnavailableBlocks.push_back(DepBB);
1499 continue;
1500 }
1501 }
1502 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD));
1503 continue;
1504 }
1505
1506 UnavailableBlocks.push_back(DepBB);
1507 }
1508 }
1509
PerformLoadPRE(LoadInst * LI,AvailValInBlkVect & ValuesPerBlock,UnavailBlkVect & UnavailableBlocks)1510 bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
1511 UnavailBlkVect &UnavailableBlocks) {
1512 // Okay, we have *some* definitions of the value. This means that the value
1513 // is available in some of our (transitive) predecessors. Lets think about
1514 // doing PRE of this load. This will involve inserting a new load into the
1515 // predecessor when it's not available. We could do this in general, but
1516 // prefer to not increase code size. As such, we only do this when we know
1517 // that we only have to insert *one* load (which means we're basically moving
1518 // the load, not inserting a new one).
1519
1520 SmallPtrSet<BasicBlock *, 4> Blockers;
1521 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1522 Blockers.insert(UnavailableBlocks[i]);
1523
1524 // Let's find the first basic block with more than one predecessor. Walk
1525 // backwards through predecessors if needed.
1526 BasicBlock *LoadBB = LI->getParent();
1527 BasicBlock *TmpBB = LoadBB;
1528
1529 while (TmpBB->getSinglePredecessor()) {
1530 TmpBB = TmpBB->getSinglePredecessor();
1531 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1532 return false;
1533 if (Blockers.count(TmpBB))
1534 return false;
1535
1536 // If any of these blocks has more than one successor (i.e. if the edge we
1537 // just traversed was critical), then there are other paths through this
1538 // block along which the load may not be anticipated. Hoisting the load
1539 // above this block would be adding the load to execution paths along
1540 // which it was not previously executed.
1541 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1542 return false;
1543 }
1544
1545 assert(TmpBB);
1546 LoadBB = TmpBB;
1547
1548 // Check to see how many predecessors have the loaded value fully
1549 // available.
1550 MapVector<BasicBlock *, Value *> PredLoads;
1551 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1552 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1553 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1554 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1555 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1556
1557 SmallVector<BasicBlock *, 4> CriticalEdgePred;
1558 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1559 PI != E; ++PI) {
1560 BasicBlock *Pred = *PI;
1561 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) {
1562 continue;
1563 }
1564
1565 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1566 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1567 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1568 << Pred->getName() << "': " << *LI << '\n');
1569 return false;
1570 }
1571
1572 if (LoadBB->isLandingPad()) {
1573 DEBUG(dbgs()
1574 << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '"
1575 << Pred->getName() << "': " << *LI << '\n');
1576 return false;
1577 }
1578
1579 CriticalEdgePred.push_back(Pred);
1580 } else {
1581 // Only add the predecessors that will not be split for now.
1582 PredLoads[Pred] = nullptr;
1583 }
1584 }
1585
1586 // Decide whether PRE is profitable for this load.
1587 unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size();
1588 assert(NumUnavailablePreds != 0 &&
1589 "Fully available value should already be eliminated!");
1590
1591 // If this load is unavailable in multiple predecessors, reject it.
1592 // FIXME: If we could restructure the CFG, we could make a common pred with
1593 // all the preds that don't have an available LI and insert a new load into
1594 // that one block.
1595 if (NumUnavailablePreds != 1)
1596 return false;
1597
1598 // Split critical edges, and update the unavailable predecessors accordingly.
1599 for (BasicBlock *OrigPred : CriticalEdgePred) {
1600 BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB);
1601 assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!");
1602 PredLoads[NewPred] = nullptr;
1603 DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->"
1604 << LoadBB->getName() << '\n');
1605 }
1606
1607 // Check if the load can safely be moved to all the unavailable predecessors.
1608 bool CanDoPRE = true;
1609 SmallVector<Instruction*, 8> NewInsts;
1610 for (auto &PredLoad : PredLoads) {
1611 BasicBlock *UnavailablePred = PredLoad.first;
1612
1613 // Do PHI translation to get its value in the predecessor if necessary. The
1614 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1615
1616 // If all preds have a single successor, then we know it is safe to insert
1617 // the load on the pred (?!?), so we can insert code to materialize the
1618 // pointer if it is not available.
1619 PHITransAddr Address(LI->getPointerOperand(), DL);
1620 Value *LoadPtr = nullptr;
1621 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1622 *DT, NewInsts);
1623
1624 // If we couldn't find or insert a computation of this phi translated value,
1625 // we fail PRE.
1626 if (!LoadPtr) {
1627 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1628 << *LI->getPointerOperand() << "\n");
1629 CanDoPRE = false;
1630 break;
1631 }
1632
1633 PredLoad.second = LoadPtr;
1634 }
1635
1636 if (!CanDoPRE) {
1637 while (!NewInsts.empty()) {
1638 Instruction *I = NewInsts.pop_back_val();
1639 if (MD) MD->removeInstruction(I);
1640 I->eraseFromParent();
1641 }
1642 // HINT: Don't revert the edge-splitting as following transformation may
1643 // also need to split these critical edges.
1644 return !CriticalEdgePred.empty();
1645 }
1646
1647 // Okay, we can eliminate this load by inserting a reload in the predecessor
1648 // and using PHI construction to get the value in the other predecessors, do
1649 // it.
1650 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1651 DEBUG(if (!NewInsts.empty())
1652 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1653 << *NewInsts.back() << '\n');
1654
1655 // Assign value numbers to the new instructions.
1656 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1657 // FIXME: We really _ought_ to insert these value numbers into their
1658 // parent's availability map. However, in doing so, we risk getting into
1659 // ordering issues. If a block hasn't been processed yet, we would be
1660 // marking a value as AVAIL-IN, which isn't what we intend.
1661 VN.lookup_or_add(NewInsts[i]);
1662 }
1663
1664 for (const auto &PredLoad : PredLoads) {
1665 BasicBlock *UnavailablePred = PredLoad.first;
1666 Value *LoadPtr = PredLoad.second;
1667
1668 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1669 LI->getAlignment(),
1670 UnavailablePred->getTerminator());
1671
1672 // Transfer the old load's TBAA tag to the new load.
1673 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa))
1674 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag);
1675
1676 // Transfer DebugLoc.
1677 NewLoad->setDebugLoc(LI->getDebugLoc());
1678
1679 // Add the newly created load.
1680 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1681 NewLoad));
1682 MD->invalidateCachedPointerInfo(LoadPtr);
1683 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1684 }
1685
1686 // Perform PHI construction.
1687 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
1688 LI->replaceAllUsesWith(V);
1689 if (isa<PHINode>(V))
1690 V->takeName(LI);
1691 if (V->getType()->getScalarType()->isPointerTy())
1692 MD->invalidateCachedPointerInfo(V);
1693 markInstructionForDeletion(LI);
1694 ++NumPRELoad;
1695 return true;
1696 }
1697
1698 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1699 /// non-local by performing PHI construction.
processNonLocalLoad(LoadInst * LI)1700 bool GVN::processNonLocalLoad(LoadInst *LI) {
1701 // Step 1: Find the non-local dependencies of the load.
1702 LoadDepVect Deps;
1703 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI);
1704 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps);
1705
1706 // If we had to process more than one hundred blocks to find the
1707 // dependencies, this load isn't worth worrying about. Optimizing
1708 // it will be too expensive.
1709 unsigned NumDeps = Deps.size();
1710 if (NumDeps > 100)
1711 return false;
1712
1713 // If we had a phi translation failure, we'll have a single entry which is a
1714 // clobber in the current block. Reject this early.
1715 if (NumDeps == 1 &&
1716 !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) {
1717 DEBUG(
1718 dbgs() << "GVN: non-local load ";
1719 LI->printAsOperand(dbgs());
1720 dbgs() << " has unknown dependencies\n";
1721 );
1722 return false;
1723 }
1724
1725 // Step 2: Analyze the availability of the load
1726 AvailValInBlkVect ValuesPerBlock;
1727 UnavailBlkVect UnavailableBlocks;
1728 AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks);
1729
1730 // If we have no predecessors that produce a known value for this load, exit
1731 // early.
1732 if (ValuesPerBlock.empty())
1733 return false;
1734
1735 // Step 3: Eliminate fully redundancy.
1736 //
1737 // If all of the instructions we depend on produce a known value for this
1738 // load, then it is fully redundant and we can use PHI insertion to compute
1739 // its value. Insert PHIs and remove the fully redundant value now.
1740 if (UnavailableBlocks.empty()) {
1741 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1742
1743 // Perform PHI construction.
1744 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
1745 LI->replaceAllUsesWith(V);
1746
1747 if (isa<PHINode>(V))
1748 V->takeName(LI);
1749 if (V->getType()->getScalarType()->isPointerTy())
1750 MD->invalidateCachedPointerInfo(V);
1751 markInstructionForDeletion(LI);
1752 ++NumGVNLoad;
1753 return true;
1754 }
1755
1756 // Step 4: Eliminate partial redundancy.
1757 if (!EnablePRE || !EnableLoadPRE)
1758 return false;
1759
1760 return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks);
1761 }
1762
1763
patchReplacementInstruction(Instruction * I,Value * Repl)1764 static void patchReplacementInstruction(Instruction *I, Value *Repl) {
1765 // Patch the replacement so that it is not more restrictive than the value
1766 // being replaced.
1767 BinaryOperator *Op = dyn_cast<BinaryOperator>(I);
1768 BinaryOperator *ReplOp = dyn_cast<BinaryOperator>(Repl);
1769 if (Op && ReplOp && isa<OverflowingBinaryOperator>(Op) &&
1770 isa<OverflowingBinaryOperator>(ReplOp)) {
1771 if (ReplOp->hasNoSignedWrap() && !Op->hasNoSignedWrap())
1772 ReplOp->setHasNoSignedWrap(false);
1773 if (ReplOp->hasNoUnsignedWrap() && !Op->hasNoUnsignedWrap())
1774 ReplOp->setHasNoUnsignedWrap(false);
1775 }
1776 if (Instruction *ReplInst = dyn_cast<Instruction>(Repl)) {
1777 SmallVector<std::pair<unsigned, MDNode*>, 4> Metadata;
1778 ReplInst->getAllMetadataOtherThanDebugLoc(Metadata);
1779 for (int i = 0, n = Metadata.size(); i < n; ++i) {
1780 unsigned Kind = Metadata[i].first;
1781 MDNode *IMD = I->getMetadata(Kind);
1782 MDNode *ReplMD = Metadata[i].second;
1783 switch(Kind) {
1784 default:
1785 ReplInst->setMetadata(Kind, nullptr); // Remove unknown metadata
1786 break;
1787 case LLVMContext::MD_dbg:
1788 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1789 case LLVMContext::MD_tbaa:
1790 ReplInst->setMetadata(Kind, MDNode::getMostGenericTBAA(IMD, ReplMD));
1791 break;
1792 case LLVMContext::MD_range:
1793 ReplInst->setMetadata(Kind, MDNode::getMostGenericRange(IMD, ReplMD));
1794 break;
1795 case LLVMContext::MD_prof:
1796 llvm_unreachable("MD_prof in a non-terminator instruction");
1797 break;
1798 case LLVMContext::MD_fpmath:
1799 ReplInst->setMetadata(Kind, MDNode::getMostGenericFPMath(IMD, ReplMD));
1800 break;
1801 case LLVMContext::MD_invariant_load:
1802 // Only set the !invariant.load if it is present in both instructions.
1803 ReplInst->setMetadata(Kind, IMD);
1804 break;
1805 }
1806 }
1807 }
1808 }
1809
patchAndReplaceAllUsesWith(Instruction * I,Value * Repl)1810 static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
1811 patchReplacementInstruction(I, Repl);
1812 I->replaceAllUsesWith(Repl);
1813 }
1814
1815 /// processLoad - Attempt to eliminate a load, first by eliminating it
1816 /// locally, and then attempting non-local elimination if that fails.
processLoad(LoadInst * L)1817 bool GVN::processLoad(LoadInst *L) {
1818 if (!MD)
1819 return false;
1820
1821 if (!L->isSimple())
1822 return false;
1823
1824 if (L->use_empty()) {
1825 markInstructionForDeletion(L);
1826 return true;
1827 }
1828
1829 // ... to a pointer that has been loaded from before...
1830 MemDepResult Dep = MD->getDependency(L);
1831
1832 // If we have a clobber and target data is around, see if this is a clobber
1833 // that we can fix up through code synthesis.
1834 if (Dep.isClobber() && DL) {
1835 // Check to see if we have something like this:
1836 // store i32 123, i32* %P
1837 // %A = bitcast i32* %P to i8*
1838 // %B = gep i8* %A, i32 1
1839 // %C = load i8* %B
1840 //
1841 // We could do that by recognizing if the clobber instructions are obviously
1842 // a common base + constant offset, and if the previous store (or memset)
1843 // completely covers this load. This sort of thing can happen in bitfield
1844 // access code.
1845 Value *AvailVal = nullptr;
1846 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) {
1847 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1848 L->getPointerOperand(),
1849 DepSI, *DL);
1850 if (Offset != -1)
1851 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset,
1852 L->getType(), L, *DL);
1853 }
1854
1855 // Check to see if we have something like this:
1856 // load i32* P
1857 // load i8* (P+1)
1858 // if we have this, replace the later with an extraction from the former.
1859 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) {
1860 // If this is a clobber and L is the first instruction in its block, then
1861 // we have the first instruction in the entry block.
1862 if (DepLI == L)
1863 return false;
1864
1865 int Offset = AnalyzeLoadFromClobberingLoad(L->getType(),
1866 L->getPointerOperand(),
1867 DepLI, *DL);
1868 if (Offset != -1)
1869 AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this);
1870 }
1871
1872 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1873 // a value on from it.
1874 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1875 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1876 L->getPointerOperand(),
1877 DepMI, *DL);
1878 if (Offset != -1)
1879 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *DL);
1880 }
1881
1882 if (AvailVal) {
1883 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1884 << *AvailVal << '\n' << *L << "\n\n\n");
1885
1886 // Replace the load!
1887 L->replaceAllUsesWith(AvailVal);
1888 if (AvailVal->getType()->getScalarType()->isPointerTy())
1889 MD->invalidateCachedPointerInfo(AvailVal);
1890 markInstructionForDeletion(L);
1891 ++NumGVNLoad;
1892 return true;
1893 }
1894 }
1895
1896 // If the value isn't available, don't do anything!
1897 if (Dep.isClobber()) {
1898 DEBUG(
1899 // fast print dep, using operator<< on instruction is too slow.
1900 dbgs() << "GVN: load ";
1901 L->printAsOperand(dbgs());
1902 Instruction *I = Dep.getInst();
1903 dbgs() << " is clobbered by " << *I << '\n';
1904 );
1905 return false;
1906 }
1907
1908 // If it is defined in another block, try harder.
1909 if (Dep.isNonLocal())
1910 return processNonLocalLoad(L);
1911
1912 if (!Dep.isDef()) {
1913 DEBUG(
1914 // fast print dep, using operator<< on instruction is too slow.
1915 dbgs() << "GVN: load ";
1916 L->printAsOperand(dbgs());
1917 dbgs() << " has unknown dependence\n";
1918 );
1919 return false;
1920 }
1921
1922 Instruction *DepInst = Dep.getInst();
1923 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1924 Value *StoredVal = DepSI->getValueOperand();
1925
1926 // The store and load are to a must-aliased pointer, but they may not
1927 // actually have the same type. See if we know how to reuse the stored
1928 // value (depending on its type).
1929 if (StoredVal->getType() != L->getType()) {
1930 if (DL) {
1931 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1932 L, *DL);
1933 if (!StoredVal)
1934 return false;
1935
1936 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1937 << '\n' << *L << "\n\n\n");
1938 }
1939 else
1940 return false;
1941 }
1942
1943 // Remove it!
1944 L->replaceAllUsesWith(StoredVal);
1945 if (StoredVal->getType()->getScalarType()->isPointerTy())
1946 MD->invalidateCachedPointerInfo(StoredVal);
1947 markInstructionForDeletion(L);
1948 ++NumGVNLoad;
1949 return true;
1950 }
1951
1952 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1953 Value *AvailableVal = DepLI;
1954
1955 // The loads are of a must-aliased pointer, but they may not actually have
1956 // the same type. See if we know how to reuse the previously loaded value
1957 // (depending on its type).
1958 if (DepLI->getType() != L->getType()) {
1959 if (DL) {
1960 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(),
1961 L, *DL);
1962 if (!AvailableVal)
1963 return false;
1964
1965 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1966 << "\n" << *L << "\n\n\n");
1967 }
1968 else
1969 return false;
1970 }
1971
1972 // Remove it!
1973 patchAndReplaceAllUsesWith(L, AvailableVal);
1974 if (DepLI->getType()->getScalarType()->isPointerTy())
1975 MD->invalidateCachedPointerInfo(DepLI);
1976 markInstructionForDeletion(L);
1977 ++NumGVNLoad;
1978 return true;
1979 }
1980
1981 // If this load really doesn't depend on anything, then we must be loading an
1982 // undef value. This can happen when loading for a fresh allocation with no
1983 // intervening stores, for example.
1984 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) {
1985 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1986 markInstructionForDeletion(L);
1987 ++NumGVNLoad;
1988 return true;
1989 }
1990
1991 // If this load occurs either right after a lifetime begin,
1992 // then the loaded value is undefined.
1993 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) {
1994 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1995 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1996 markInstructionForDeletion(L);
1997 ++NumGVNLoad;
1998 return true;
1999 }
2000 }
2001
2002 // If this load follows a calloc (which zero initializes memory),
2003 // then the loaded value is zero
2004 if (isCallocLikeFn(DepInst, TLI)) {
2005 L->replaceAllUsesWith(Constant::getNullValue(L->getType()));
2006 markInstructionForDeletion(L);
2007 ++NumGVNLoad;
2008 return true;
2009 }
2010
2011 return false;
2012 }
2013
2014 // findLeader - In order to find a leader for a given value number at a
2015 // specific basic block, we first obtain the list of all Values for that number,
2016 // and then scan the list to find one whose block dominates the block in
2017 // question. This is fast because dominator tree queries consist of only
2018 // a few comparisons of DFS numbers.
findLeader(const BasicBlock * BB,uint32_t num)2019 Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) {
2020 LeaderTableEntry Vals = LeaderTable[num];
2021 if (!Vals.Val) return nullptr;
2022
2023 Value *Val = nullptr;
2024 if (DT->dominates(Vals.BB, BB)) {
2025 Val = Vals.Val;
2026 if (isa<Constant>(Val)) return Val;
2027 }
2028
2029 LeaderTableEntry* Next = Vals.Next;
2030 while (Next) {
2031 if (DT->dominates(Next->BB, BB)) {
2032 if (isa<Constant>(Next->Val)) return Next->Val;
2033 if (!Val) Val = Next->Val;
2034 }
2035
2036 Next = Next->Next;
2037 }
2038
2039 return Val;
2040 }
2041
2042 /// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the
2043 /// use is dominated by the given basic block. Returns the number of uses that
2044 /// were replaced.
replaceAllDominatedUsesWith(Value * From,Value * To,const BasicBlockEdge & Root)2045 unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
2046 const BasicBlockEdge &Root) {
2047 unsigned Count = 0;
2048 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
2049 UI != UE; ) {
2050 Use &U = *UI++;
2051
2052 if (DT->dominates(Root, U)) {
2053 U.set(To);
2054 ++Count;
2055 }
2056 }
2057 return Count;
2058 }
2059
2060 /// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return
2061 /// true if every path from the entry block to 'Dst' passes via this edge. In
2062 /// particular 'Dst' must not be reachable via another edge from 'Src'.
isOnlyReachableViaThisEdge(const BasicBlockEdge & E,DominatorTree * DT)2063 static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E,
2064 DominatorTree *DT) {
2065 // While in theory it is interesting to consider the case in which Dst has
2066 // more than one predecessor, because Dst might be part of a loop which is
2067 // only reachable from Src, in practice it is pointless since at the time
2068 // GVN runs all such loops have preheaders, which means that Dst will have
2069 // been changed to have only one predecessor, namely Src.
2070 const BasicBlock *Pred = E.getEnd()->getSinglePredecessor();
2071 const BasicBlock *Src = E.getStart();
2072 assert((!Pred || Pred == Src) && "No edge between these basic blocks!");
2073 (void)Src;
2074 return Pred != nullptr;
2075 }
2076
2077 /// propagateEquality - The given values are known to be equal in every block
2078 /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
2079 /// 'RHS' everywhere in the scope. Returns whether a change was made.
propagateEquality(Value * LHS,Value * RHS,const BasicBlockEdge & Root)2080 bool GVN::propagateEquality(Value *LHS, Value *RHS,
2081 const BasicBlockEdge &Root) {
2082 SmallVector<std::pair<Value*, Value*>, 4> Worklist;
2083 Worklist.push_back(std::make_pair(LHS, RHS));
2084 bool Changed = false;
2085 // For speed, compute a conservative fast approximation to
2086 // DT->dominates(Root, Root.getEnd());
2087 bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT);
2088
2089 while (!Worklist.empty()) {
2090 std::pair<Value*, Value*> Item = Worklist.pop_back_val();
2091 LHS = Item.first; RHS = Item.second;
2092
2093 if (LHS == RHS) continue;
2094 assert(LHS->getType() == RHS->getType() && "Equality but unequal types!");
2095
2096 // Don't try to propagate equalities between constants.
2097 if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue;
2098
2099 // Prefer a constant on the right-hand side, or an Argument if no constants.
2100 if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
2101 std::swap(LHS, RHS);
2102 assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!");
2103
2104 // If there is no obvious reason to prefer the left-hand side over the right-
2105 // hand side, ensure the longest lived term is on the right-hand side, so the
2106 // shortest lived term will be replaced by the longest lived. This tends to
2107 // expose more simplifications.
2108 uint32_t LVN = VN.lookup_or_add(LHS);
2109 if ((isa<Argument>(LHS) && isa<Argument>(RHS)) ||
2110 (isa<Instruction>(LHS) && isa<Instruction>(RHS))) {
2111 // Move the 'oldest' value to the right-hand side, using the value number as
2112 // a proxy for age.
2113 uint32_t RVN = VN.lookup_or_add(RHS);
2114 if (LVN < RVN) {
2115 std::swap(LHS, RHS);
2116 LVN = RVN;
2117 }
2118 }
2119
2120 // If value numbering later sees that an instruction in the scope is equal
2121 // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve
2122 // the invariant that instructions only occur in the leader table for their
2123 // own value number (this is used by removeFromLeaderTable), do not do this
2124 // if RHS is an instruction (if an instruction in the scope is morphed into
2125 // LHS then it will be turned into RHS by the next GVN iteration anyway, so
2126 // using the leader table is about compiling faster, not optimizing better).
2127 // The leader table only tracks basic blocks, not edges. Only add to if we
2128 // have the simple case where the edge dominates the end.
2129 if (RootDominatesEnd && !isa<Instruction>(RHS))
2130 addToLeaderTable(LVN, RHS, Root.getEnd());
2131
2132 // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As
2133 // LHS always has at least one use that is not dominated by Root, this will
2134 // never do anything if LHS has only one use.
2135 if (!LHS->hasOneUse()) {
2136 unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
2137 Changed |= NumReplacements > 0;
2138 NumGVNEqProp += NumReplacements;
2139 }
2140
2141 // Now try to deduce additional equalities from this one. For example, if the
2142 // known equality was "(A != B)" == "false" then it follows that A and B are
2143 // equal in the scope. Only boolean equalities with an explicit true or false
2144 // RHS are currently supported.
2145 if (!RHS->getType()->isIntegerTy(1))
2146 // Not a boolean equality - bail out.
2147 continue;
2148 ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
2149 if (!CI)
2150 // RHS neither 'true' nor 'false' - bail out.
2151 continue;
2152 // Whether RHS equals 'true'. Otherwise it equals 'false'.
2153 bool isKnownTrue = CI->isAllOnesValue();
2154 bool isKnownFalse = !isKnownTrue;
2155
2156 // If "A && B" is known true then both A and B are known true. If "A || B"
2157 // is known false then both A and B are known false.
2158 Value *A, *B;
2159 if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
2160 (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
2161 Worklist.push_back(std::make_pair(A, RHS));
2162 Worklist.push_back(std::make_pair(B, RHS));
2163 continue;
2164 }
2165
2166 // If we are propagating an equality like "(A == B)" == "true" then also
2167 // propagate the equality A == B. When propagating a comparison such as
2168 // "(A >= B)" == "true", replace all instances of "A < B" with "false".
2169 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
2170 Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
2171
2172 // If "A == B" is known true, or "A != B" is known false, then replace
2173 // A with B everywhere in the scope.
2174 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
2175 (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
2176 Worklist.push_back(std::make_pair(Op0, Op1));
2177
2178 // If "A >= B" is known true, replace "A < B" with false everywhere.
2179 CmpInst::Predicate NotPred = Cmp->getInversePredicate();
2180 Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
2181 // Since we don't have the instruction "A < B" immediately to hand, work out
2182 // the value number that it would have and use that to find an appropriate
2183 // instruction (if any).
2184 uint32_t NextNum = VN.getNextUnusedValueNumber();
2185 uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
2186 // If the number we were assigned was brand new then there is no point in
2187 // looking for an instruction realizing it: there cannot be one!
2188 if (Num < NextNum) {
2189 Value *NotCmp = findLeader(Root.getEnd(), Num);
2190 if (NotCmp && isa<Instruction>(NotCmp)) {
2191 unsigned NumReplacements =
2192 replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
2193 Changed |= NumReplacements > 0;
2194 NumGVNEqProp += NumReplacements;
2195 }
2196 }
2197 // Ensure that any instruction in scope that gets the "A < B" value number
2198 // is replaced with false.
2199 // The leader table only tracks basic blocks, not edges. Only add to if we
2200 // have the simple case where the edge dominates the end.
2201 if (RootDominatesEnd)
2202 addToLeaderTable(Num, NotVal, Root.getEnd());
2203
2204 continue;
2205 }
2206 }
2207
2208 return Changed;
2209 }
2210
2211 /// processInstruction - When calculating availability, handle an instruction
2212 /// by inserting it into the appropriate sets
processInstruction(Instruction * I)2213 bool GVN::processInstruction(Instruction *I) {
2214 // Ignore dbg info intrinsics.
2215 if (isa<DbgInfoIntrinsic>(I))
2216 return false;
2217
2218 // If the instruction can be easily simplified then do so now in preference
2219 // to value numbering it. Value numbering often exposes redundancies, for
2220 // example if it determines that %y is equal to %x then the instruction
2221 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify.
2222 if (Value *V = SimplifyInstruction(I, DL, TLI, DT)) {
2223 I->replaceAllUsesWith(V);
2224 if (MD && V->getType()->getScalarType()->isPointerTy())
2225 MD->invalidateCachedPointerInfo(V);
2226 markInstructionForDeletion(I);
2227 ++NumGVNSimpl;
2228 return true;
2229 }
2230
2231 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
2232 if (processLoad(LI))
2233 return true;
2234
2235 unsigned Num = VN.lookup_or_add(LI);
2236 addToLeaderTable(Num, LI, LI->getParent());
2237 return false;
2238 }
2239
2240 // For conditional branches, we can perform simple conditional propagation on
2241 // the condition value itself.
2242 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
2243 if (!BI->isConditional())
2244 return false;
2245
2246 if (isa<Constant>(BI->getCondition()))
2247 return processFoldableCondBr(BI);
2248
2249 Value *BranchCond = BI->getCondition();
2250 BasicBlock *TrueSucc = BI->getSuccessor(0);
2251 BasicBlock *FalseSucc = BI->getSuccessor(1);
2252 // Avoid multiple edges early.
2253 if (TrueSucc == FalseSucc)
2254 return false;
2255
2256 BasicBlock *Parent = BI->getParent();
2257 bool Changed = false;
2258
2259 Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext());
2260 BasicBlockEdge TrueE(Parent, TrueSucc);
2261 Changed |= propagateEquality(BranchCond, TrueVal, TrueE);
2262
2263 Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext());
2264 BasicBlockEdge FalseE(Parent, FalseSucc);
2265 Changed |= propagateEquality(BranchCond, FalseVal, FalseE);
2266
2267 return Changed;
2268 }
2269
2270 // For switches, propagate the case values into the case destinations.
2271 if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
2272 Value *SwitchCond = SI->getCondition();
2273 BasicBlock *Parent = SI->getParent();
2274 bool Changed = false;
2275
2276 // Remember how many outgoing edges there are to every successor.
2277 SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
2278 for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
2279 ++SwitchEdges[SI->getSuccessor(i)];
2280
2281 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2282 i != e; ++i) {
2283 BasicBlock *Dst = i.getCaseSuccessor();
2284 // If there is only a single edge, propagate the case value into it.
2285 if (SwitchEdges.lookup(Dst) == 1) {
2286 BasicBlockEdge E(Parent, Dst);
2287 Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E);
2288 }
2289 }
2290 return Changed;
2291 }
2292
2293 // Instructions with void type don't return a value, so there's
2294 // no point in trying to find redundancies in them.
2295 if (I->getType()->isVoidTy()) return false;
2296
2297 uint32_t NextNum = VN.getNextUnusedValueNumber();
2298 unsigned Num = VN.lookup_or_add(I);
2299
2300 // Allocations are always uniquely numbered, so we can save time and memory
2301 // by fast failing them.
2302 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) {
2303 addToLeaderTable(Num, I, I->getParent());
2304 return false;
2305 }
2306
2307 // If the number we were assigned was a brand new VN, then we don't
2308 // need to do a lookup to see if the number already exists
2309 // somewhere in the domtree: it can't!
2310 if (Num >= NextNum) {
2311 addToLeaderTable(Num, I, I->getParent());
2312 return false;
2313 }
2314
2315 // Perform fast-path value-number based elimination of values inherited from
2316 // dominators.
2317 Value *repl = findLeader(I->getParent(), Num);
2318 if (!repl) {
2319 // Failure, just remember this instance for future use.
2320 addToLeaderTable(Num, I, I->getParent());
2321 return false;
2322 }
2323
2324 // Remove it!
2325 patchAndReplaceAllUsesWith(I, repl);
2326 if (MD && repl->getType()->getScalarType()->isPointerTy())
2327 MD->invalidateCachedPointerInfo(repl);
2328 markInstructionForDeletion(I);
2329 return true;
2330 }
2331
2332 /// runOnFunction - This is the main transformation entry point for a function.
runOnFunction(Function & F)2333 bool GVN::runOnFunction(Function& F) {
2334 if (skipOptnoneFunction(F))
2335 return false;
2336
2337 if (!NoLoads)
2338 MD = &getAnalysis<MemoryDependenceAnalysis>();
2339 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2340 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
2341 DL = DLP ? &DLP->getDataLayout() : nullptr;
2342 TLI = &getAnalysis<TargetLibraryInfo>();
2343 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2344 VN.setMemDep(MD);
2345 VN.setDomTree(DT);
2346
2347 bool Changed = false;
2348 bool ShouldContinue = true;
2349
2350 // Merge unconditional branches, allowing PRE to catch more
2351 // optimization opportunities.
2352 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2353 BasicBlock *BB = FI++;
2354
2355 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2356 if (removedBlock) ++NumGVNBlocks;
2357
2358 Changed |= removedBlock;
2359 }
2360
2361 unsigned Iteration = 0;
2362 while (ShouldContinue) {
2363 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2364 ShouldContinue = iterateOnFunction(F);
2365 Changed |= ShouldContinue;
2366 ++Iteration;
2367 }
2368
2369 if (EnablePRE) {
2370 // Fabricate val-num for dead-code in order to suppress assertion in
2371 // performPRE().
2372 assignValNumForDeadCode();
2373 bool PREChanged = true;
2374 while (PREChanged) {
2375 PREChanged = performPRE(F);
2376 Changed |= PREChanged;
2377 }
2378 }
2379
2380 // FIXME: Should perform GVN again after PRE does something. PRE can move
2381 // computations into blocks where they become fully redundant. Note that
2382 // we can't do this until PRE's critical edge splitting updates memdep.
2383 // Actually, when this happens, we should just fully integrate PRE into GVN.
2384
2385 cleanupGlobalSets();
2386 // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each
2387 // iteration.
2388 DeadBlocks.clear();
2389
2390 return Changed;
2391 }
2392
2393
processBlock(BasicBlock * BB)2394 bool GVN::processBlock(BasicBlock *BB) {
2395 // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function
2396 // (and incrementing BI before processing an instruction).
2397 assert(InstrsToErase.empty() &&
2398 "We expect InstrsToErase to be empty across iterations");
2399 if (DeadBlocks.count(BB))
2400 return false;
2401
2402 bool ChangedFunction = false;
2403
2404 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2405 BI != BE;) {
2406 ChangedFunction |= processInstruction(BI);
2407 if (InstrsToErase.empty()) {
2408 ++BI;
2409 continue;
2410 }
2411
2412 // If we need some instructions deleted, do it now.
2413 NumGVNInstr += InstrsToErase.size();
2414
2415 // Avoid iterator invalidation.
2416 bool AtStart = BI == BB->begin();
2417 if (!AtStart)
2418 --BI;
2419
2420 for (SmallVectorImpl<Instruction *>::iterator I = InstrsToErase.begin(),
2421 E = InstrsToErase.end(); I != E; ++I) {
2422 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2423 if (MD) MD->removeInstruction(*I);
2424 DEBUG(verifyRemoved(*I));
2425 (*I)->eraseFromParent();
2426 }
2427 InstrsToErase.clear();
2428
2429 if (AtStart)
2430 BI = BB->begin();
2431 else
2432 ++BI;
2433 }
2434
2435 return ChangedFunction;
2436 }
2437
2438 /// performPRE - Perform a purely local form of PRE that looks for diamond
2439 /// control flow patterns and attempts to perform simple PRE at the join point.
performPRE(Function & F)2440 bool GVN::performPRE(Function &F) {
2441 bool Changed = false;
2442 SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap;
2443 for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) {
2444 // Nothing to PRE in the entry block.
2445 if (CurrentBlock == &F.getEntryBlock()) continue;
2446
2447 // Don't perform PRE on a landing pad.
2448 if (CurrentBlock->isLandingPad()) continue;
2449
2450 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2451 BE = CurrentBlock->end(); BI != BE; ) {
2452 Instruction *CurInst = BI++;
2453
2454 if (isa<AllocaInst>(CurInst) ||
2455 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2456 CurInst->getType()->isVoidTy() ||
2457 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2458 isa<DbgInfoIntrinsic>(CurInst))
2459 continue;
2460
2461 // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from
2462 // sinking the compare again, and it would force the code generator to
2463 // move the i1 from processor flags or predicate registers into a general
2464 // purpose register.
2465 if (isa<CmpInst>(CurInst))
2466 continue;
2467
2468 // We don't currently value number ANY inline asm calls.
2469 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2470 if (CallI->isInlineAsm())
2471 continue;
2472
2473 uint32_t ValNo = VN.lookup(CurInst);
2474
2475 // Look for the predecessors for PRE opportunities. We're
2476 // only trying to solve the basic diamond case, where
2477 // a value is computed in the successor and one predecessor,
2478 // but not the other. We also explicitly disallow cases
2479 // where the successor is its own predecessor, because they're
2480 // more complicated to get right.
2481 unsigned NumWith = 0;
2482 unsigned NumWithout = 0;
2483 BasicBlock *PREPred = nullptr;
2484 predMap.clear();
2485
2486 for (pred_iterator PI = pred_begin(CurrentBlock),
2487 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2488 BasicBlock *P = *PI;
2489 // We're not interested in PRE where the block is its
2490 // own predecessor, or in blocks with predecessors
2491 // that are not reachable.
2492 if (P == CurrentBlock) {
2493 NumWithout = 2;
2494 break;
2495 } else if (!DT->isReachableFromEntry(P)) {
2496 NumWithout = 2;
2497 break;
2498 }
2499
2500 Value* predV = findLeader(P, ValNo);
2501 if (!predV) {
2502 predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P));
2503 PREPred = P;
2504 ++NumWithout;
2505 } else if (predV == CurInst) {
2506 /* CurInst dominates this predecessor. */
2507 NumWithout = 2;
2508 break;
2509 } else {
2510 predMap.push_back(std::make_pair(predV, P));
2511 ++NumWith;
2512 }
2513 }
2514
2515 // Don't do PRE when it might increase code size, i.e. when
2516 // we would need to insert instructions in more than one pred.
2517 if (NumWithout != 1 || NumWith == 0)
2518 continue;
2519
2520 // Don't do PRE across indirect branch.
2521 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2522 continue;
2523
2524 // We can't do PRE safely on a critical edge, so instead we schedule
2525 // the edge to be split and perform the PRE the next time we iterate
2526 // on the function.
2527 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2528 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2529 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2530 continue;
2531 }
2532
2533 // Instantiate the expression in the predecessor that lacked it.
2534 // Because we are going top-down through the block, all value numbers
2535 // will be available in the predecessor by the time we need them. Any
2536 // that weren't originally present will have been instantiated earlier
2537 // in this loop.
2538 Instruction *PREInstr = CurInst->clone();
2539 bool success = true;
2540 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2541 Value *Op = PREInstr->getOperand(i);
2542 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2543 continue;
2544
2545 if (Value *V = findLeader(PREPred, VN.lookup(Op))) {
2546 PREInstr->setOperand(i, V);
2547 } else {
2548 success = false;
2549 break;
2550 }
2551 }
2552
2553 // Fail out if we encounter an operand that is not available in
2554 // the PRE predecessor. This is typically because of loads which
2555 // are not value numbered precisely.
2556 if (!success) {
2557 DEBUG(verifyRemoved(PREInstr));
2558 delete PREInstr;
2559 continue;
2560 }
2561
2562 PREInstr->insertBefore(PREPred->getTerminator());
2563 PREInstr->setName(CurInst->getName() + ".pre");
2564 PREInstr->setDebugLoc(CurInst->getDebugLoc());
2565 VN.add(PREInstr, ValNo);
2566 ++NumGVNPRE;
2567
2568 // Update the availability map to include the new instruction.
2569 addToLeaderTable(ValNo, PREInstr, PREPred);
2570
2571 // Create a PHI to make the value available in this block.
2572 PHINode* Phi = PHINode::Create(CurInst->getType(), predMap.size(),
2573 CurInst->getName() + ".pre-phi",
2574 CurrentBlock->begin());
2575 for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
2576 if (Value *V = predMap[i].first)
2577 Phi->addIncoming(V, predMap[i].second);
2578 else
2579 Phi->addIncoming(PREInstr, PREPred);
2580 }
2581
2582 VN.add(Phi, ValNo);
2583 addToLeaderTable(ValNo, Phi, CurrentBlock);
2584 Phi->setDebugLoc(CurInst->getDebugLoc());
2585 CurInst->replaceAllUsesWith(Phi);
2586 if (Phi->getType()->getScalarType()->isPointerTy()) {
2587 // Because we have added a PHI-use of the pointer value, it has now
2588 // "escaped" from alias analysis' perspective. We need to inform
2589 // AA of this.
2590 for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee;
2591 ++ii) {
2592 unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
2593 VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj));
2594 }
2595
2596 if (MD)
2597 MD->invalidateCachedPointerInfo(Phi);
2598 }
2599 VN.erase(CurInst);
2600 removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
2601
2602 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2603 if (MD) MD->removeInstruction(CurInst);
2604 DEBUG(verifyRemoved(CurInst));
2605 CurInst->eraseFromParent();
2606 Changed = true;
2607 }
2608 }
2609
2610 if (splitCriticalEdges())
2611 Changed = true;
2612
2613 return Changed;
2614 }
2615
2616 /// Split the critical edge connecting the given two blocks, and return
2617 /// the block inserted to the critical edge.
splitCriticalEdges(BasicBlock * Pred,BasicBlock * Succ)2618 BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) {
2619 BasicBlock *BB = SplitCriticalEdge(Pred, Succ, this);
2620 if (MD)
2621 MD->invalidateCachedPredecessors();
2622 return BB;
2623 }
2624
2625 /// splitCriticalEdges - Split critical edges found during the previous
2626 /// iteration that may enable further optimization.
splitCriticalEdges()2627 bool GVN::splitCriticalEdges() {
2628 if (toSplit.empty())
2629 return false;
2630 do {
2631 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2632 SplitCriticalEdge(Edge.first, Edge.second, this);
2633 } while (!toSplit.empty());
2634 if (MD) MD->invalidateCachedPredecessors();
2635 return true;
2636 }
2637
2638 /// iterateOnFunction - Executes one iteration of GVN
iterateOnFunction(Function & F)2639 bool GVN::iterateOnFunction(Function &F) {
2640 cleanupGlobalSets();
2641
2642 // Top-down walk of the dominator tree
2643 bool Changed = false;
2644 #if 0
2645 // Needed for value numbering with phi construction to work.
2646 ReversePostOrderTraversal<Function*> RPOT(&F);
2647 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2648 RE = RPOT.end(); RI != RE; ++RI)
2649 Changed |= processBlock(*RI);
2650 #else
2651 // Save the blocks this function have before transformation begins. GVN may
2652 // split critical edge, and hence may invalidate the RPO/DT iterator.
2653 //
2654 std::vector<BasicBlock *> BBVect;
2655 BBVect.reserve(256);
2656 for (DomTreeNode *x : depth_first(DT->getRootNode()))
2657 BBVect.push_back(x->getBlock());
2658
2659 for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end();
2660 I != E; I++)
2661 Changed |= processBlock(*I);
2662 #endif
2663
2664 return Changed;
2665 }
2666
cleanupGlobalSets()2667 void GVN::cleanupGlobalSets() {
2668 VN.clear();
2669 LeaderTable.clear();
2670 TableAllocator.Reset();
2671 }
2672
2673 /// verifyRemoved - Verify that the specified instruction does not occur in our
2674 /// internal data structures.
verifyRemoved(const Instruction * Inst) const2675 void GVN::verifyRemoved(const Instruction *Inst) const {
2676 VN.verifyRemoved(Inst);
2677
2678 // Walk through the value number scope to make sure the instruction isn't
2679 // ferreted away in it.
2680 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator
2681 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) {
2682 const LeaderTableEntry *Node = &I->second;
2683 assert(Node->Val != Inst && "Inst still in value numbering scope!");
2684
2685 while (Node->Next) {
2686 Node = Node->Next;
2687 assert(Node->Val != Inst && "Inst still in value numbering scope!");
2688 }
2689 }
2690 }
2691
2692 // BB is declared dead, which implied other blocks become dead as well. This
2693 // function is to add all these blocks to "DeadBlocks". For the dead blocks'
2694 // live successors, update their phi nodes by replacing the operands
2695 // corresponding to dead blocks with UndefVal.
2696 //
addDeadBlock(BasicBlock * BB)2697 void GVN::addDeadBlock(BasicBlock *BB) {
2698 SmallVector<BasicBlock *, 4> NewDead;
2699 SmallSetVector<BasicBlock *, 4> DF;
2700
2701 NewDead.push_back(BB);
2702 while (!NewDead.empty()) {
2703 BasicBlock *D = NewDead.pop_back_val();
2704 if (DeadBlocks.count(D))
2705 continue;
2706
2707 // All blocks dominated by D are dead.
2708 SmallVector<BasicBlock *, 8> Dom;
2709 DT->getDescendants(D, Dom);
2710 DeadBlocks.insert(Dom.begin(), Dom.end());
2711
2712 // Figure out the dominance-frontier(D).
2713 for (SmallVectorImpl<BasicBlock *>::iterator I = Dom.begin(),
2714 E = Dom.end(); I != E; I++) {
2715 BasicBlock *B = *I;
2716 for (succ_iterator SI = succ_begin(B), SE = succ_end(B); SI != SE; SI++) {
2717 BasicBlock *S = *SI;
2718 if (DeadBlocks.count(S))
2719 continue;
2720
2721 bool AllPredDead = true;
2722 for (pred_iterator PI = pred_begin(S), PE = pred_end(S); PI != PE; PI++)
2723 if (!DeadBlocks.count(*PI)) {
2724 AllPredDead = false;
2725 break;
2726 }
2727
2728 if (!AllPredDead) {
2729 // S could be proved dead later on. That is why we don't update phi
2730 // operands at this moment.
2731 DF.insert(S);
2732 } else {
2733 // While S is not dominated by D, it is dead by now. This could take
2734 // place if S already have a dead predecessor before D is declared
2735 // dead.
2736 NewDead.push_back(S);
2737 }
2738 }
2739 }
2740 }
2741
2742 // For the dead blocks' live successors, update their phi nodes by replacing
2743 // the operands corresponding to dead blocks with UndefVal.
2744 for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end();
2745 I != E; I++) {
2746 BasicBlock *B = *I;
2747 if (DeadBlocks.count(B))
2748 continue;
2749
2750 SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B));
2751 for (SmallVectorImpl<BasicBlock *>::iterator PI = Preds.begin(),
2752 PE = Preds.end(); PI != PE; PI++) {
2753 BasicBlock *P = *PI;
2754
2755 if (!DeadBlocks.count(P))
2756 continue;
2757
2758 if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) {
2759 if (BasicBlock *S = splitCriticalEdges(P, B))
2760 DeadBlocks.insert(P = S);
2761 }
2762
2763 for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) {
2764 PHINode &Phi = cast<PHINode>(*II);
2765 Phi.setIncomingValue(Phi.getBasicBlockIndex(P),
2766 UndefValue::get(Phi.getType()));
2767 }
2768 }
2769 }
2770 }
2771
2772 // If the given branch is recognized as a foldable branch (i.e. conditional
2773 // branch with constant condition), it will perform following analyses and
2774 // transformation.
2775 // 1) If the dead out-coming edge is a critical-edge, split it. Let
2776 // R be the target of the dead out-coming edge.
2777 // 1) Identify the set of dead blocks implied by the branch's dead outcoming
2778 // edge. The result of this step will be {X| X is dominated by R}
2779 // 2) Identify those blocks which haves at least one dead prodecessor. The
2780 // result of this step will be dominance-frontier(R).
2781 // 3) Update the PHIs in DF(R) by replacing the operands corresponding to
2782 // dead blocks with "UndefVal" in an hope these PHIs will optimized away.
2783 //
2784 // Return true iff *NEW* dead code are found.
processFoldableCondBr(BranchInst * BI)2785 bool GVN::processFoldableCondBr(BranchInst *BI) {
2786 if (!BI || BI->isUnconditional())
2787 return false;
2788
2789 ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
2790 if (!Cond)
2791 return false;
2792
2793 BasicBlock *DeadRoot = Cond->getZExtValue() ?
2794 BI->getSuccessor(1) : BI->getSuccessor(0);
2795 if (DeadBlocks.count(DeadRoot))
2796 return false;
2797
2798 if (!DeadRoot->getSinglePredecessor())
2799 DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot);
2800
2801 addDeadBlock(DeadRoot);
2802 return true;
2803 }
2804
2805 // performPRE() will trigger assert if it come across an instruciton without
2806 // associated val-num. As it normally has far more live instructions than dead
2807 // instructions, it makes more sense just to "fabricate" a val-number for the
2808 // dead code than checking if instruction involved is dead or not.
assignValNumForDeadCode()2809 void GVN::assignValNumForDeadCode() {
2810 for (SetVector<BasicBlock *>::iterator I = DeadBlocks.begin(),
2811 E = DeadBlocks.end(); I != E; I++) {
2812 BasicBlock *BB = *I;
2813 for (BasicBlock::iterator II = BB->begin(), EE = BB->end();
2814 II != EE; II++) {
2815 Instruction *Inst = &*II;
2816 unsigned ValNum = VN.lookup_or_add(Inst);
2817 addToLeaderTable(ValNum, Inst, BB);
2818 }
2819 }
2820 }
2821