1 //===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This pass performs various transformations related to eliminating memcpy
10 // calls, or transforming sets of stores into memset's.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Transforms/Scalar/MemCpyOptimizer.h"
15 #include "llvm/ADT/DenseSet.h"
16 #include "llvm/ADT/None.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/ADT/iterator_range.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/AssumptionCache.h"
23 #include "llvm/Analysis/GlobalsModRef.h"
24 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
25 #include "llvm/Analysis/MemoryLocation.h"
26 #include "llvm/Analysis/TargetLibraryInfo.h"
27 #include "llvm/Transforms/Utils/Local.h"
28 #include "llvm/Analysis/ValueTracking.h"
29 #include "llvm/IR/Argument.h"
30 #include "llvm/IR/BasicBlock.h"
31 #include "llvm/IR/CallSite.h"
32 #include "llvm/IR/Constants.h"
33 #include "llvm/IR/DataLayout.h"
34 #include "llvm/IR/DerivedTypes.h"
35 #include "llvm/IR/Dominators.h"
36 #include "llvm/IR/Function.h"
37 #include "llvm/IR/GetElementPtrTypeIterator.h"
38 #include "llvm/IR/GlobalVariable.h"
39 #include "llvm/IR/IRBuilder.h"
40 #include "llvm/IR/InstrTypes.h"
41 #include "llvm/IR/Instruction.h"
42 #include "llvm/IR/Instructions.h"
43 #include "llvm/IR/IntrinsicInst.h"
44 #include "llvm/IR/Intrinsics.h"
45 #include "llvm/IR/LLVMContext.h"
46 #include "llvm/IR/Module.h"
47 #include "llvm/IR/Operator.h"
48 #include "llvm/IR/PassManager.h"
49 #include "llvm/IR/Type.h"
50 #include "llvm/IR/User.h"
51 #include "llvm/IR/Value.h"
52 #include "llvm/Pass.h"
53 #include "llvm/Support/Casting.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Support/MathExtras.h"
56 #include "llvm/Support/raw_ostream.h"
57 #include "llvm/Transforms/Scalar.h"
65 #define DEBUG_TYPE "memcpyopt"
67 STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
68 STATISTIC(NumMemSetInfer, "Number of memsets inferred");
69 STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy");
70 STATISTIC(NumCpyToSet, "Number of memcpys converted to memset");
72 static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
73 bool &VariableIdxFound,
74 const DataLayout &DL) {
75 // Skip over the first indices.
76 gep_type_iterator GTI = gep_type_begin(GEP);
77 for (unsigned i = 1; i != Idx; ++i, ++GTI)
80 // Compute the offset implied by the rest of the indices.
82 for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
83 ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
85 return VariableIdxFound = true;
86 if (OpC->isZero()) continue; // No offset.
88 // Handle struct indices, which add their field offset to the pointer.
89 if (StructType *STy = GTI.getStructTypeOrNull()) {
90 Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
94 // Otherwise, we have a sequential type like an array or vector. Multiply
95 // the index by the ElementSize.
96 uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
97 Offset += Size*OpC->getSExtValue();
103 /// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
104 /// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
105 /// might be &A[40]. In this case offset would be -8.
106 static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
107 const DataLayout &DL) {
108 Ptr1 = Ptr1->stripPointerCasts();
109 Ptr2 = Ptr2->stripPointerCasts();
111 // Handle the trivial case first.
117 GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
118 GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
120 bool VariableIdxFound = false;
122 // If one pointer is a GEP and the other isn't, then see if the GEP is a
123 // constant offset from the base, as in "P" and "gep P, 1".
124 if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
125 Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
126 return !VariableIdxFound;
129 if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
130 Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
131 return !VariableIdxFound;
134 // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
135 // base. After that base, they may have some number of common (and
136 // potentially variable) indices. After that they handle some constant
137 // offset, which determines their offset from each other. At this point, we
138 // handle no other case.
139 if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
142 // Skip any common indices and track the GEP types.
144 for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
145 if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
148 int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
149 int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
150 if (VariableIdxFound) return false;
152 Offset = Offset2-Offset1;
158 /// Represents a range of memset'd bytes with the ByteVal value.
159 /// This allows us to analyze stores like:
164 /// which sometimes happens with stores to arrays of structs etc. When we see
165 /// the first store, we make a range [1, 2). The second store extends the range
166 /// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
167 /// two ranges into [0, 3) which is memset'able.
169 // Start/End - A semi range that describes the span that this range covers.
170 // The range is closed at the start and open at the end: [Start, End).
173 /// StartPtr - The getelementptr instruction that points to the start of the
177 /// Alignment - The known alignment of the first store.
180 /// TheStores - The actual stores that make up this range.
181 SmallVector<Instruction*, 16> TheStores;
183 bool isProfitableToUseMemset(const DataLayout &DL) const;
186 } // end anonymous namespace
188 bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const {
189 // If we found more than 4 stores to merge or 16 bytes, use memset.
190 if (TheStores.size() >= 4 || End-Start >= 16) return true;
192 // If there is nothing to merge, don't do anything.
193 if (TheStores.size() < 2) return false;
195 // If any of the stores are a memset, then it is always good to extend the
197 for (Instruction *SI : TheStores)
198 if (!isa<StoreInst>(SI))
201 // Assume that the code generator is capable of merging pairs of stores
202 // together if it wants to.
203 if (TheStores.size() == 2) return false;
205 // If we have fewer than 8 stores, it can still be worthwhile to do this.
206 // For example, merging 4 i8 stores into an i32 store is useful almost always.
207 // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
208 // memset will be split into 2 32-bit stores anyway) and doing so can
209 // pessimize the llvm optimizer.
211 // Since we don't have perfect knowledge here, make some assumptions: assume
212 // the maximum GPR width is the same size as the largest legal integer
213 // size. If so, check to see whether we will end up actually reducing the
214 // number of stores used.
215 unsigned Bytes = unsigned(End-Start);
216 unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8;
219 unsigned NumPointerStores = Bytes / MaxIntSize;
221 // Assume the remaining bytes if any are done a byte at a time.
222 unsigned NumByteStores = Bytes % MaxIntSize;
224 // If we will reduce the # stores (according to this heuristic), do the
225 // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
227 return TheStores.size() > NumPointerStores+NumByteStores;
233 using range_iterator = SmallVectorImpl<MemsetRange>::iterator;
235 /// A sorted list of the memset ranges.
236 SmallVector<MemsetRange, 8> Ranges;
238 const DataLayout &DL;
241 MemsetRanges(const DataLayout &DL) : DL(DL) {}
243 using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator;
245 const_iterator begin() const { return Ranges.begin(); }
246 const_iterator end() const { return Ranges.end(); }
247 bool empty() const { return Ranges.empty(); }
249 void addInst(int64_t OffsetFromFirst, Instruction *Inst) {
250 if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
251 addStore(OffsetFromFirst, SI);
253 addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst));
256 void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
257 int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType());
259 addRange(OffsetFromFirst, StoreSize,
260 SI->getPointerOperand(), SI->getAlignment(), SI);
263 void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
264 int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue();
265 addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI);
268 void addRange(int64_t Start, int64_t Size, Value *Ptr,
269 unsigned Alignment, Instruction *Inst);
272 } // end anonymous namespace
274 /// Add a new store to the MemsetRanges data structure. This adds a
275 /// new range for the specified store at the specified offset, merging into
276 /// existing ranges as appropriate.
277 void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr,
278 unsigned Alignment, Instruction *Inst) {
279 int64_t End = Start+Size;
281 range_iterator I = partition_point(
282 Ranges, [=](const MemsetRange &O) { return O.End < Start; });
284 // We now know that I == E, in which case we didn't find anything to merge
285 // with, or that Start <= I->End. If End < I->Start or I == E, then we need
286 // to insert a new range. Handle this now.
287 if (I == Ranges.end() || End < I->Start) {
288 MemsetRange &R = *Ranges.insert(I, MemsetRange());
292 R.Alignment = Alignment;
293 R.TheStores.push_back(Inst);
297 // This store overlaps with I, add it.
298 I->TheStores.push_back(Inst);
300 // At this point, we may have an interval that completely contains our store.
301 // If so, just add it to the interval and return.
302 if (I->Start <= Start && I->End >= End)
305 // Now we know that Start <= I->End and End >= I->Start so the range overlaps
306 // but is not entirely contained within the range.
308 // See if the range extends the start of the range. In this case, it couldn't
309 // possibly cause it to join the prior range, because otherwise we would have
311 if (Start < I->Start) {
314 I->Alignment = Alignment;
317 // Now we know that Start <= I->End and Start >= I->Start (so the startpoint
318 // is in or right at the end of I), and that End >= I->Start. Extend I out to
322 range_iterator NextI = I;
323 while (++NextI != Ranges.end() && End >= NextI->Start) {
324 // Merge the range in.
325 I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
326 if (NextI->End > I->End)
334 //===----------------------------------------------------------------------===//
335 // MemCpyOptLegacyPass Pass
336 //===----------------------------------------------------------------------===//
340 class MemCpyOptLegacyPass : public FunctionPass {
344 static char ID; // Pass identification, replacement for typeid
346 MemCpyOptLegacyPass() : FunctionPass(ID) {
347 initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry());
350 bool runOnFunction(Function &F) override;
353 // This transformation requires dominator postdominator info
354 void getAnalysisUsage(AnalysisUsage &AU) const override {
355 AU.setPreservesCFG();
356 AU.addRequired<AssumptionCacheTracker>();
357 AU.addRequired<DominatorTreeWrapperPass>();
358 AU.addRequired<MemoryDependenceWrapperPass>();
359 AU.addRequired<AAResultsWrapperPass>();
360 AU.addRequired<TargetLibraryInfoWrapperPass>();
361 AU.addPreserved<GlobalsAAWrapperPass>();
362 AU.addPreserved<MemoryDependenceWrapperPass>();
366 } // end anonymous namespace
368 char MemCpyOptLegacyPass::ID = 0;
370 /// The public interface to this file...
371 FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); }
373 INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
375 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
376 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
377 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
378 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
379 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
380 INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
381 INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
384 /// When scanning forward over instructions, we look for some other patterns to
385 /// fold away. In particular, this looks for stores to neighboring locations of
386 /// memory. If it sees enough consecutive ones, it attempts to merge them
387 /// together into a memcpy/memset.
388 Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,
391 const DataLayout &DL = StartInst->getModule()->getDataLayout();
393 // Okay, so we now have a single store that can be splatable. Scan to find
394 // all subsequent stores of the same value to offset from the same pointer.
395 // Join these together into ranges, so we can decide whether contiguous blocks
397 MemsetRanges Ranges(DL);
399 BasicBlock::iterator BI(StartInst);
400 for (++BI; !BI->isTerminator(); ++BI) {
401 if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) {
402 // If the instruction is readnone, ignore it, otherwise bail out. We
403 // don't even allow readonly here because we don't want something like:
404 // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
405 if (BI->mayWriteToMemory() || BI->mayReadFromMemory())
410 if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
411 // If this is a store, see if we can merge it in.
412 if (!NextStore->isSimple()) break;
414 // Check to see if this stored value is of the same byte-splattable value.
415 Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL);
416 if (isa<UndefValue>(ByteVal) && StoredByte)
417 ByteVal = StoredByte;
418 if (ByteVal != StoredByte)
421 // Check to see if this store is to a constant offset from the start ptr.
423 if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
427 Ranges.addStore(Offset, NextStore);
429 MemSetInst *MSI = cast<MemSetInst>(BI);
431 if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
432 !isa<ConstantInt>(MSI->getLength()))
435 // Check to see if this store is to a constant offset from the start ptr.
437 if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
440 Ranges.addMemSet(Offset, MSI);
444 // If we have no ranges, then we just had a single store with nothing that
445 // could be merged in. This is a very common case of course.
449 // If we had at least one store that could be merged in, add the starting
450 // store as well. We try to avoid this unless there is at least something
451 // interesting as a small compile-time optimization.
452 Ranges.addInst(0, StartInst);
454 // If we create any memsets, we put it right before the first instruction that
455 // isn't part of the memset block. This ensure that the memset is dominated
456 // by any addressing instruction needed by the start of the block.
457 IRBuilder<> Builder(&*BI);
459 // Now that we have full information about ranges, loop over the ranges and
460 // emit memset's for anything big enough to be worthwhile.
461 Instruction *AMemSet = nullptr;
462 for (const MemsetRange &Range : Ranges) {
463 if (Range.TheStores.size() == 1) continue;
465 // If it is profitable to lower this range to memset, do so now.
466 if (!Range.isProfitableToUseMemset(DL))
469 // Otherwise, we do want to transform this! Create a new memset.
470 // Get the starting pointer of the block.
471 StartPtr = Range.StartPtr;
473 // Determine alignment
474 unsigned Alignment = Range.Alignment;
475 if (Alignment == 0) {
477 cast<PointerType>(StartPtr->getType())->getElementType();
478 Alignment = DL.getABITypeAlignment(EltType);
482 Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment);
484 LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI
485 : Range.TheStores) dbgs()
487 dbgs() << "With: " << *AMemSet << '\n');
489 if (!Range.TheStores.empty())
490 AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
492 // Zap all the stores.
493 for (Instruction *SI : Range.TheStores) {
494 MD->removeInstruction(SI);
495 SI->eraseFromParent();
503 static unsigned findStoreAlignment(const DataLayout &DL, const StoreInst *SI) {
504 unsigned StoreAlign = SI->getAlignment();
506 StoreAlign = DL.getABITypeAlignment(SI->getOperand(0)->getType());
510 static unsigned findLoadAlignment(const DataLayout &DL, const LoadInst *LI) {
511 unsigned LoadAlign = LI->getAlignment();
513 LoadAlign = DL.getABITypeAlignment(LI->getType());
517 static unsigned findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
518 const LoadInst *LI) {
519 unsigned StoreAlign = findStoreAlignment(DL, SI);
520 unsigned LoadAlign = findLoadAlignment(DL, LI);
521 return MinAlign(StoreAlign, LoadAlign);
524 // This method try to lift a store instruction before position P.
525 // It will lift the store and its argument + that anything that
526 // may alias with these.
527 // The method returns true if it was successful.
528 static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P,
529 const LoadInst *LI) {
530 // If the store alias this position, early bail out.
531 MemoryLocation StoreLoc = MemoryLocation::get(SI);
532 if (isModOrRefSet(AA.getModRefInfo(P, StoreLoc)))
535 // Keep track of the arguments of all instruction we plan to lift
536 // so we can make sure to lift them as well if appropriate.
537 DenseSet<Instruction*> Args;
538 if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand()))
539 if (Ptr->getParent() == SI->getParent())
542 // Instruction to lift before P.
543 SmallVector<Instruction*, 8> ToLift;
545 // Memory locations of lifted instructions.
546 SmallVector<MemoryLocation, 8> MemLocs{StoreLoc};
549 SmallVector<const CallBase *, 8> Calls;
551 const MemoryLocation LoadLoc = MemoryLocation::get(LI);
553 for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
556 bool MayAlias = isModOrRefSet(AA.getModRefInfo(C, None));
558 bool NeedLift = false;
562 NeedLift = llvm::any_of(MemLocs, [C, &AA](const MemoryLocation &ML) {
563 return isModOrRefSet(AA.getModRefInfo(C, ML));
567 NeedLift = llvm::any_of(Calls, [C, &AA](const CallBase *Call) {
568 return isModOrRefSet(AA.getModRefInfo(C, Call));
576 // Since LI is implicitly moved downwards past the lifted instructions,
577 // none of them may modify its source.
578 if (isModSet(AA.getModRefInfo(C, LoadLoc)))
580 else if (const auto *Call = dyn_cast<CallBase>(C)) {
581 // If we can't lift this before P, it's game over.
582 if (isModOrRefSet(AA.getModRefInfo(P, Call)))
585 Calls.push_back(Call);
586 } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) {
587 // If we can't lift this before P, it's game over.
588 auto ML = MemoryLocation::get(C);
589 if (isModOrRefSet(AA.getModRefInfo(P, ML)))
592 MemLocs.push_back(ML);
594 // We don't know how to lift this instruction.
599 for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
600 if (auto *A = dyn_cast<Instruction>(C->getOperand(k)))
601 if (A->getParent() == SI->getParent())
605 // We made it, we need to lift
606 for (auto *I : llvm::reverse(ToLift)) {
607 LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n");
614 bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
615 if (!SI->isSimple()) return false;
617 // Avoid merging nontemporal stores since the resulting
618 // memcpy/memset would not be able to preserve the nontemporal hint.
619 // In theory we could teach how to propagate the !nontemporal metadata to
620 // memset calls. However, that change would force the backend to
621 // conservatively expand !nontemporal memset calls back to sequences of
622 // store instructions (effectively undoing the merging).
623 if (SI->getMetadata(LLVMContext::MD_nontemporal))
626 const DataLayout &DL = SI->getModule()->getDataLayout();
628 // Load to store forwarding can be interpreted as memcpy.
629 if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
630 if (LI->isSimple() && LI->hasOneUse() &&
631 LI->getParent() == SI->getParent()) {
633 auto *T = LI->getType();
634 if (T->isAggregateType()) {
635 AliasAnalysis &AA = LookupAliasAnalysis();
636 MemoryLocation LoadLoc = MemoryLocation::get(LI);
638 // We use alias analysis to check if an instruction may store to
639 // the memory we load from in between the load and the store. If
640 // such an instruction is found, we try to promote there instead
641 // of at the store position.
643 for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
644 if (isModSet(AA.getModRefInfo(&I, LoadLoc))) {
650 // We found an instruction that may write to the loaded memory.
651 // We can try to promote at this position instead of the store
652 // position if nothing alias the store memory after this and the store
653 // destination is not in the range.
655 if (!moveUp(AA, SI, P, LI))
659 // If a valid insertion position is found, then we can promote
660 // the load/store pair to a memcpy.
662 // If we load from memory that may alias the memory we store to,
663 // memmove must be used to preserve semantic. If not, memcpy can
665 bool UseMemMove = false;
666 if (!AA.isNoAlias(MemoryLocation::get(SI), LoadLoc))
669 uint64_t Size = DL.getTypeStoreSize(T);
671 IRBuilder<> Builder(P);
674 M = Builder.CreateMemMove(
675 SI->getPointerOperand(), findStoreAlignment(DL, SI),
676 LI->getPointerOperand(), findLoadAlignment(DL, LI), Size);
678 M = Builder.CreateMemCpy(
679 SI->getPointerOperand(), findStoreAlignment(DL, SI),
680 LI->getPointerOperand(), findLoadAlignment(DL, LI), Size);
682 LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => "
685 MD->removeInstruction(SI);
686 SI->eraseFromParent();
687 MD->removeInstruction(LI);
688 LI->eraseFromParent();
691 // Make sure we do not invalidate the iterator.
692 BBI = M->getIterator();
697 // Detect cases where we're performing call slot forwarding, but
698 // happen to be using a load-store pair to implement it, rather than
700 MemDepResult ldep = MD->getDependency(LI);
701 CallInst *C = nullptr;
702 if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
703 C = dyn_cast<CallInst>(ldep.getInst());
706 // Check that nothing touches the dest of the "copy" between
707 // the call and the store.
708 Value *CpyDest = SI->getPointerOperand()->stripPointerCasts();
709 bool CpyDestIsLocal = isa<AllocaInst>(CpyDest);
710 AliasAnalysis &AA = LookupAliasAnalysis();
711 MemoryLocation StoreLoc = MemoryLocation::get(SI);
712 for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator();
714 if (isModOrRefSet(AA.getModRefInfo(&*I, StoreLoc))) {
718 // The store to dest may never happen if an exception can be thrown
719 // between the load and the store.
720 if (I->mayThrow() && !CpyDestIsLocal) {
728 bool changed = performCallSlotOptzn(
729 LI, SI->getPointerOperand()->stripPointerCasts(),
730 LI->getPointerOperand()->stripPointerCasts(),
731 DL.getTypeStoreSize(SI->getOperand(0)->getType()),
732 findCommonAlignment(DL, SI, LI), C);
734 MD->removeInstruction(SI);
735 SI->eraseFromParent();
736 MD->removeInstruction(LI);
737 LI->eraseFromParent();
745 // There are two cases that are interesting for this code to handle: memcpy
746 // and memset. Right now we only handle memset.
748 // Ensure that the value being stored is something that can be memset'able a
749 // byte at a time like "0" or "-1" or any width, as well as things like
750 // 0xA0A0A0A0 and 0.0.
751 auto *V = SI->getOperand(0);
752 if (Value *ByteVal = isBytewiseValue(V, DL)) {
753 if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
755 BBI = I->getIterator(); // Don't invalidate iterator.
759 // If we have an aggregate, we try to promote it to memset regardless
760 // of opportunity for merging as it can expose optimization opportunities
761 // in subsequent passes.
762 auto *T = V->getType();
763 if (T->isAggregateType()) {
764 uint64_t Size = DL.getTypeStoreSize(T);
765 unsigned Align = SI->getAlignment();
767 Align = DL.getABITypeAlignment(T);
768 IRBuilder<> Builder(SI);
770 Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size, Align);
772 LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n");
774 MD->removeInstruction(SI);
775 SI->eraseFromParent();
778 // Make sure we do not invalidate the iterator.
779 BBI = M->getIterator();
787 bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
788 // See if there is another memset or store neighboring this memset which
789 // allows us to widen out the memset to do a single larger store.
790 if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
791 if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
793 BBI = I->getIterator(); // Don't invalidate iterator.
799 /// Takes a memcpy and a call that it depends on,
800 /// and checks for the possibility of a call slot optimization by having
801 /// the call write its result directly into the destination of the memcpy.
802 bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpy, Value *cpyDest,
803 Value *cpySrc, uint64_t cpyLen,
804 unsigned cpyAlign, CallInst *C) {
805 // The general transformation to keep in mind is
807 // call @func(..., src, ...)
808 // memcpy(dest, src, ...)
812 // memcpy(dest, src, ...)
813 // call @func(..., dest, ...)
815 // Since moving the memcpy is technically awkward, we additionally check that
816 // src only holds uninitialized values at the moment of the call, meaning that
817 // the memcpy can be discarded rather than moved.
819 // Lifetime marks shouldn't be operated on.
820 if (Function *F = C->getCalledFunction())
821 if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start)
824 // Deliberately get the source and destination with bitcasts stripped away,
825 // because we'll need to do type comparisons based on the underlying type.
828 // Require that src be an alloca. This simplifies the reasoning considerably.
829 AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
833 ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
837 const DataLayout &DL = cpy->getModule()->getDataLayout();
838 uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) *
839 srcArraySize->getZExtValue();
841 if (cpyLen < srcSize)
844 // Check that accessing the first srcSize bytes of dest will not cause a
845 // trap. Otherwise the transform is invalid since it might cause a trap
846 // to occur earlier than it otherwise would.
847 if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) {
848 // The destination is an alloca. Check it is larger than srcSize.
849 ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
853 uint64_t destSize = DL.getTypeAllocSize(A->getAllocatedType()) *
854 destArraySize->getZExtValue();
856 if (destSize < srcSize)
858 } else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
859 // The store to dest may never happen if the call can throw.
863 if (A->getDereferenceableBytes() < srcSize) {
864 // If the destination is an sret parameter then only accesses that are
865 // outside of the returned struct type can trap.
866 if (!A->hasStructRetAttr())
869 Type *StructTy = cast<PointerType>(A->getType())->getElementType();
870 if (!StructTy->isSized()) {
871 // The call may never return and hence the copy-instruction may never
872 // be executed, and therefore it's not safe to say "the destination
873 // has at least <cpyLen> bytes, as implied by the copy-instruction",
877 uint64_t destSize = DL.getTypeAllocSize(StructTy);
878 if (destSize < srcSize)
885 // Check that dest points to memory that is at least as aligned as src.
886 unsigned srcAlign = srcAlloca->getAlignment();
888 srcAlign = DL.getABITypeAlignment(srcAlloca->getAllocatedType());
889 bool isDestSufficientlyAligned = srcAlign <= cpyAlign;
890 // If dest is not aligned enough and we can't increase its alignment then
892 if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest))
895 // Check that src is not accessed except via the call and the memcpy. This
896 // guarantees that it holds only undefined values when passed in (so the final
897 // memcpy can be dropped), that it is not read or written between the call and
898 // the memcpy, and that writing beyond the end of it is undefined.
899 SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(),
900 srcAlloca->user_end());
901 while (!srcUseList.empty()) {
902 User *U = srcUseList.pop_back_val();
904 if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
905 for (User *UU : U->users())
906 srcUseList.push_back(UU);
909 if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
910 if (!G->hasAllZeroIndices())
913 for (User *UU : U->users())
914 srcUseList.push_back(UU);
917 if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
918 if (IT->isLifetimeStartOrEnd())
921 if (U != C && U != cpy)
925 // Check that src isn't captured by the called function since the
926 // transformation can cause aliasing issues in that case.
927 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
928 if (CS.getArgument(i) == cpySrc && !CS.doesNotCapture(i))
931 // Since we're changing the parameter to the callsite, we need to make sure
932 // that what would be the new parameter dominates the callsite.
933 DominatorTree &DT = LookupDomTree();
934 if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest))
935 if (!DT.dominates(cpyDestInst, C))
938 // In addition to knowing that the call does not access src in some
939 // unexpected manner, for example via a global, which we deduce from
940 // the use analysis, we also need to know that it does not sneakily
941 // access dest. We rely on AA to figure this out for us.
942 AliasAnalysis &AA = LookupAliasAnalysis();
943 ModRefInfo MR = AA.getModRefInfo(C, cpyDest, LocationSize::precise(srcSize));
944 // If necessary, perform additional analysis.
945 if (isModOrRefSet(MR))
946 MR = AA.callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), &DT);
947 if (isModOrRefSet(MR))
950 // We can't create address space casts here because we don't know if they're
951 // safe for the target.
952 if (cpySrc->getType()->getPointerAddressSpace() !=
953 cpyDest->getType()->getPointerAddressSpace())
955 for (unsigned i = 0; i < CS.arg_size(); ++i)
956 if (CS.getArgument(i)->stripPointerCasts() == cpySrc &&
957 cpySrc->getType()->getPointerAddressSpace() !=
958 CS.getArgument(i)->getType()->getPointerAddressSpace())
961 // All the checks have passed, so do the transformation.
962 bool changedArgument = false;
963 for (unsigned i = 0; i < CS.arg_size(); ++i)
964 if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
965 Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest
966 : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
967 cpyDest->getName(), C);
968 changedArgument = true;
969 if (CS.getArgument(i)->getType() == Dest->getType())
970 CS.setArgument(i, Dest);
972 CS.setArgument(i, CastInst::CreatePointerCast(Dest,
973 CS.getArgument(i)->getType(), Dest->getName(), C));
976 if (!changedArgument)
979 // If the destination wasn't sufficiently aligned then increase its alignment.
980 if (!isDestSufficientlyAligned) {
981 assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!");
982 cast<AllocaInst>(cpyDest)->setAlignment(srcAlign);
985 // Drop any cached information about the call, because we may have changed
986 // its dependence information by changing its parameter.
987 MD->removeInstruction(C);
989 // Update AA metadata
990 // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
991 // handled here, but combineMetadata doesn't support them yet
992 unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
993 LLVMContext::MD_noalias,
994 LLVMContext::MD_invariant_group,
995 LLVMContext::MD_access_group};
996 combineMetadata(C, cpy, KnownIDs, true);
998 // Remove the memcpy.
999 MD->removeInstruction(cpy);
1005 /// We've found that the (upward scanning) memory dependence of memcpy 'M' is
1006 /// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can.
1007 bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
1009 // We can only transforms memcpy's where the dest of one is the source of the
1011 if (M->getSource() != MDep->getDest() || MDep->isVolatile())
1014 // If dep instruction is reading from our current input, then it is a noop
1015 // transfer and substituting the input won't change this instruction. Just
1016 // ignore the input and let someone else zap MDep. This handles cases like:
1019 if (M->getSource() == MDep->getSource())
1022 // Second, the length of the memcpy's must be the same, or the preceding one
1023 // must be larger than the following one.
1024 ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
1025 ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength());
1026 if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
1029 AliasAnalysis &AA = LookupAliasAnalysis();
1031 // Verify that the copied-from memory doesn't change in between the two
1032 // transfers. For example, in:
1036 // It would be invalid to transform the second memcpy into memcpy(c <- b).
1038 // TODO: If the code between M and MDep is transparent to the destination "c",
1039 // then we could still perform the xform by moving M up to the first memcpy.
1041 // NOTE: This is conservative, it will stop on any read from the source loc,
1042 // not just the defining memcpy.
1043 MemDepResult SourceDep =
1044 MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
1045 M->getIterator(), M->getParent());
1046 if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
1049 // If the dest of the second might alias the source of the first, then the
1050 // source and dest might overlap. We still want to eliminate the intermediate
1051 // value, but we have to generate a memmove instead of memcpy.
1052 bool UseMemMove = false;
1053 if (!AA.isNoAlias(MemoryLocation::getForDest(M),
1054 MemoryLocation::getForSource(MDep)))
1057 // If all checks passed, then we can transform M.
1058 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
1059 << *MDep << '\n' << *M << '\n');
1061 // TODO: Is this worth it if we're creating a less aligned memcpy? For
1062 // example we could be moving from movaps -> movq on x86.
1063 IRBuilder<> Builder(M);
1065 Builder.CreateMemMove(M->getRawDest(), M->getDestAlignment(),
1066 MDep->getRawSource(), MDep->getSourceAlignment(),
1067 M->getLength(), M->isVolatile());
1069 Builder.CreateMemCpy(M->getRawDest(), M->getDestAlignment(),
1070 MDep->getRawSource(), MDep->getSourceAlignment(),
1071 M->getLength(), M->isVolatile());
1073 // Remove the instruction we're replacing.
1074 MD->removeInstruction(M);
1075 M->eraseFromParent();
1080 /// We've found that the (upward scanning) memory dependence of \p MemCpy is
1081 /// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that
1082 /// weren't copied over by \p MemCpy.
1084 /// In other words, transform:
1086 /// memset(dst, c, dst_size);
1087 /// memcpy(dst, src, src_size);
1091 /// memcpy(dst, src, src_size);
1092 /// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
1094 bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
1095 MemSetInst *MemSet) {
1096 // We can only transform memset/memcpy with the same destination.
1097 if (MemSet->getDest() != MemCpy->getDest())
1100 // Check that there are no other dependencies on the memset destination.
1101 MemDepResult DstDepInfo =
1102 MD->getPointerDependencyFrom(MemoryLocation::getForDest(MemSet), false,
1103 MemCpy->getIterator(), MemCpy->getParent());
1104 if (DstDepInfo.getInst() != MemSet)
1107 // Use the same i8* dest as the memcpy, killing the memset dest if different.
1108 Value *Dest = MemCpy->getRawDest();
1109 Value *DestSize = MemSet->getLength();
1110 Value *SrcSize = MemCpy->getLength();
1112 // By default, create an unaligned memset.
1114 // If Dest is aligned, and SrcSize is constant, use the minimum alignment
1116 const unsigned DestAlign =
1117 std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment());
1119 if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
1120 Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
1122 IRBuilder<> Builder(MemCpy);
1124 // If the sizes have different types, zext the smaller one.
1125 if (DestSize->getType() != SrcSize->getType()) {
1126 if (DestSize->getType()->getIntegerBitWidth() >
1127 SrcSize->getType()->getIntegerBitWidth())
1128 SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType());
1130 DestSize = Builder.CreateZExt(DestSize, SrcSize->getType());
1133 Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize);
1134 Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize);
1135 Value *MemsetLen = Builder.CreateSelect(
1136 Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff);
1137 Builder.CreateMemSet(
1138 Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest,
1140 MemSet->getOperand(1), MemsetLen, Align);
1142 MD->removeInstruction(MemSet);
1143 MemSet->eraseFromParent();
1147 /// Determine whether the instruction has undefined content for the given Size,
1148 /// either because it was freshly alloca'd or started its lifetime.
1149 static bool hasUndefContents(Instruction *I, ConstantInt *Size) {
1150 if (isa<AllocaInst>(I))
1153 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
1154 if (II->getIntrinsicID() == Intrinsic::lifetime_start)
1155 if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
1156 if (LTSize->getZExtValue() >= Size->getZExtValue())
1162 /// Transform memcpy to memset when its source was just memset.
1163 /// In other words, turn:
1165 /// memset(dst1, c, dst1_size);
1166 /// memcpy(dst2, dst1, dst2_size);
1170 /// memset(dst1, c, dst1_size);
1171 /// memset(dst2, c, dst2_size);
1173 /// When dst2_size <= dst1_size.
1175 /// The \p MemCpy must have a Constant length.
1176 bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy,
1177 MemSetInst *MemSet) {
1178 AliasAnalysis &AA = LookupAliasAnalysis();
1180 // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
1181 // memcpying from the same address. Otherwise it is hard to reason about.
1182 if (!AA.isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
1185 // A known memset size is required.
1186 ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
1190 // Make sure the memcpy doesn't read any more than what the memset wrote.
1191 // Don't worry about sizes larger than i64.
1192 ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
1193 if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) {
1194 // If the memcpy is larger than the memset, but the memory was undef prior
1195 // to the memset, we can just ignore the tail. Technically we're only
1196 // interested in the bytes from MemSetSize..CopySize here, but as we can't
1197 // easily represent this location, we use the full 0..CopySize range.
1198 MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy);
1199 MemDepResult DepInfo = MD->getPointerDependencyFrom(
1200 MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent());
1201 if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize))
1202 CopySize = MemSetSize;
1207 IRBuilder<> Builder(MemCpy);
1208 Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1),
1209 CopySize, MemCpy->getDestAlignment());
1213 /// Perform simplification of memcpy's. If we have memcpy A
1214 /// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
1215 /// B to be a memcpy from X to Z (or potentially a memmove, depending on
1216 /// circumstances). This allows later passes to remove the first memcpy
1218 bool MemCpyOptPass::processMemCpy(MemCpyInst *M) {
1219 // We can only optimize non-volatile memcpy's.
1220 if (M->isVolatile()) return false;
1222 // If the source and destination of the memcpy are the same, then zap it.
1223 if (M->getSource() == M->getDest()) {
1224 MD->removeInstruction(M);
1225 M->eraseFromParent();
1229 // If copying from a constant, try to turn the memcpy into a memset.
1230 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource()))
1231 if (GV->isConstant() && GV->hasDefinitiveInitializer())
1232 if (Value *ByteVal = isBytewiseValue(GV->getInitializer(),
1233 M->getModule()->getDataLayout())) {
1234 IRBuilder<> Builder(M);
1235 Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
1236 M->getDestAlignment(), false);
1237 MD->removeInstruction(M);
1238 M->eraseFromParent();
1243 MemDepResult DepInfo = MD->getDependency(M);
1245 // Try to turn a partially redundant memset + memcpy into
1246 // memcpy + smaller memset. We don't need the memcpy size for this.
1247 if (DepInfo.isClobber())
1248 if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst()))
1249 if (processMemSetMemCpyDependence(M, MDep))
1252 // The optimizations after this point require the memcpy size.
1253 ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
1254 if (!CopySize) return false;
1256 // There are four possible optimizations we can do for memcpy:
1257 // a) memcpy-memcpy xform which exposes redundance for DSE.
1258 // b) call-memcpy xform for return slot optimization.
1259 // c) memcpy from freshly alloca'd space or space that has just started its
1260 // lifetime copies undefined data, and we can therefore eliminate the
1261 // memcpy in favor of the data that was already at the destination.
1262 // d) memcpy from a just-memset'd source can be turned into memset.
1263 if (DepInfo.isClobber()) {
1264 if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
1265 // FIXME: Can we pass in either of dest/src alignment here instead
1266 // of conservatively taking the minimum?
1267 unsigned Align = MinAlign(M->getDestAlignment(), M->getSourceAlignment());
1268 if (performCallSlotOptzn(M, M->getDest(), M->getSource(),
1269 CopySize->getZExtValue(), Align,
1271 MD->removeInstruction(M);
1272 M->eraseFromParent();
1278 MemoryLocation SrcLoc = MemoryLocation::getForSource(M);
1279 MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
1280 SrcLoc, true, M->getIterator(), M->getParent());
1282 if (SrcDepInfo.isClobber()) {
1283 if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
1284 return processMemCpyMemCpyDependence(M, MDep);
1285 } else if (SrcDepInfo.isDef()) {
1286 if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) {
1287 MD->removeInstruction(M);
1288 M->eraseFromParent();
1294 if (SrcDepInfo.isClobber())
1295 if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
1296 if (performMemCpyToMemSetOptzn(M, MDep)) {
1297 MD->removeInstruction(M);
1298 M->eraseFromParent();
1306 /// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
1308 bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
1309 AliasAnalysis &AA = LookupAliasAnalysis();
1311 if (!TLI->has(LibFunc_memmove))
1314 // See if the pointers alias.
1315 if (!AA.isNoAlias(MemoryLocation::getForDest(M),
1316 MemoryLocation::getForSource(M)))
1319 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M
1322 // If not, then we know we can transform this.
1323 Type *ArgTys[3] = { M->getRawDest()->getType(),
1324 M->getRawSource()->getType(),
1325 M->getLength()->getType() };
1326 M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(),
1327 Intrinsic::memcpy, ArgTys));
1329 // MemDep may have over conservative information about this instruction, just
1330 // conservatively flush it from the cache.
1331 MD->removeInstruction(M);
1337 /// This is called on every byval argument in call sites.
1338 bool MemCpyOptPass::processByValArgument(CallSite CS, unsigned ArgNo) {
1339 const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout();
1340 // Find out what feeds this byval argument.
1341 Value *ByValArg = CS.getArgument(ArgNo);
1342 Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType();
1343 uint64_t ByValSize = DL.getTypeAllocSize(ByValTy);
1344 MemDepResult DepInfo = MD->getPointerDependencyFrom(
1345 MemoryLocation(ByValArg, LocationSize::precise(ByValSize)), true,
1346 CS.getInstruction()->getIterator(), CS.getInstruction()->getParent());
1347 if (!DepInfo.isClobber())
1350 // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by
1351 // a memcpy, see if we can byval from the source of the memcpy instead of the
1353 MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst());
1354 if (!MDep || MDep->isVolatile() ||
1355 ByValArg->stripPointerCasts() != MDep->getDest())
1358 // The length of the memcpy must be larger or equal to the size of the byval.
1359 ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
1360 if (!C1 || C1->getValue().getZExtValue() < ByValSize)
1363 // Get the alignment of the byval. If the call doesn't specify the alignment,
1364 // then it is some target specific value that we can't know.
1365 unsigned ByValAlign = CS.getParamAlignment(ArgNo);
1366 if (ByValAlign == 0) return false;
1368 // If it is greater than the memcpy, then we check to see if we can force the
1369 // source of the memcpy to the alignment we need. If we fail, we bail out.
1370 AssumptionCache &AC = LookupAssumptionCache();
1371 DominatorTree &DT = LookupDomTree();
1372 if (MDep->getSourceAlignment() < ByValAlign &&
1373 getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL,
1374 CS.getInstruction(), &AC, &DT) < ByValAlign)
1377 // The address space of the memcpy source must match the byval argument
1378 if (MDep->getSource()->getType()->getPointerAddressSpace() !=
1379 ByValArg->getType()->getPointerAddressSpace())
1382 // Verify that the copied-from memory doesn't change in between the memcpy and
1387 // It would be invalid to transform the second memcpy into foo(*b).
1389 // NOTE: This is conservative, it will stop on any read from the source loc,
1390 // not just the defining memcpy.
1391 MemDepResult SourceDep = MD->getPointerDependencyFrom(
1392 MemoryLocation::getForSource(MDep), false,
1393 CS.getInstruction()->getIterator(), MDep->getParent());
1394 if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
1397 Value *TmpCast = MDep->getSource();
1398 if (MDep->getSource()->getType() != ByValArg->getType())
1399 TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
1400 "tmpcast", CS.getInstruction());
1402 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
1403 << " " << *MDep << "\n"
1404 << " " << *CS.getInstruction() << "\n");
1406 // Otherwise we're good! Update the byval argument.
1407 CS.setArgument(ArgNo, TmpCast);
1412 /// Executes one iteration of MemCpyOptPass.
1413 bool MemCpyOptPass::iterateOnFunction(Function &F) {
1414 bool MadeChange = false;
1416 DominatorTree &DT = LookupDomTree();
1418 // Walk all instruction in the function.
1419 for (BasicBlock &BB : F) {
1420 // Skip unreachable blocks. For example processStore assumes that an
1421 // instruction in a BB can't be dominated by a later instruction in the
1422 // same BB (which is a scenario that can happen for an unreachable BB that
1423 // has itself as a predecessor).
1424 if (!DT.isReachableFromEntry(&BB))
1427 for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
1428 // Avoid invalidating the iterator.
1429 Instruction *I = &*BI++;
1431 bool RepeatInstruction = false;
1433 if (StoreInst *SI = dyn_cast<StoreInst>(I))
1434 MadeChange |= processStore(SI, BI);
1435 else if (MemSetInst *M = dyn_cast<MemSetInst>(I))
1436 RepeatInstruction = processMemSet(M, BI);
1437 else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
1438 RepeatInstruction = processMemCpy(M);
1439 else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I))
1440 RepeatInstruction = processMemMove(M);
1441 else if (auto CS = CallSite(I)) {
1442 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
1443 if (CS.isByValArgument(i))
1444 MadeChange |= processByValArgument(CS, i);
1447 // Reprocess the instruction if desired.
1448 if (RepeatInstruction) {
1449 if (BI != BB.begin())
1459 PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) {
1460 auto &MD = AM.getResult<MemoryDependenceAnalysis>(F);
1461 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
1463 auto LookupAliasAnalysis = [&]() -> AliasAnalysis & {
1464 return AM.getResult<AAManager>(F);
1466 auto LookupAssumptionCache = [&]() -> AssumptionCache & {
1467 return AM.getResult<AssumptionAnalysis>(F);
1469 auto LookupDomTree = [&]() -> DominatorTree & {
1470 return AM.getResult<DominatorTreeAnalysis>(F);
1473 bool MadeChange = runImpl(F, &MD, &TLI, LookupAliasAnalysis,
1474 LookupAssumptionCache, LookupDomTree);
1476 return PreservedAnalyses::all();
1478 PreservedAnalyses PA;
1479 PA.preserveSet<CFGAnalyses>();
1480 PA.preserve<GlobalsAA>();
1481 PA.preserve<MemoryDependenceAnalysis>();
1485 bool MemCpyOptPass::runImpl(
1486 Function &F, MemoryDependenceResults *MD_, TargetLibraryInfo *TLI_,
1487 std::function<AliasAnalysis &()> LookupAliasAnalysis_,
1488 std::function<AssumptionCache &()> LookupAssumptionCache_,
1489 std::function<DominatorTree &()> LookupDomTree_) {
1490 bool MadeChange = false;
1493 LookupAliasAnalysis = std::move(LookupAliasAnalysis_);
1494 LookupAssumptionCache = std::move(LookupAssumptionCache_);
1495 LookupDomTree = std::move(LookupDomTree_);
1497 // If we don't have at least memset and memcpy, there is little point of doing
1498 // anything here. These are required by a freestanding implementation, so if
1499 // even they are disabled, there is no point in trying hard.
1500 if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
1504 if (!iterateOnFunction(F))
1513 /// This is the main transformation entry point for a function.
1514 bool MemCpyOptLegacyPass::runOnFunction(Function &F) {
1515 if (skipFunction(F))
1518 auto *MD = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
1519 auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1521 auto LookupAliasAnalysis = [this]() -> AliasAnalysis & {
1522 return getAnalysis<AAResultsWrapperPass>().getAAResults();
1524 auto LookupAssumptionCache = [this, &F]() -> AssumptionCache & {
1525 return getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
1527 auto LookupDomTree = [this]() -> DominatorTree & {
1528 return getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1531 return Impl.runImpl(F, MD, TLI, LookupAliasAnalysis, LookupAssumptionCache,