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Diffstat (limited to 'llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp | 1453 |
1 files changed, 1453 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp new file mode 100644 index 000000000000..2364748efb05 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp @@ -0,0 +1,1453 @@ +//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This pass performs various transformations related to eliminating memcpy +// calls, or transforming sets of stores into memset's. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/MemCpyOptimizer.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/None.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/MemoryDependenceAnalysis.h" +#include "llvm/Analysis/MemoryLocation.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Argument.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GetElementPtrTypeIterator.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/PassManager.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include <algorithm> +#include <cassert> +#include <cstdint> +#include <utility> + +using namespace llvm; + +#define DEBUG_TYPE "memcpyopt" + +STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted"); +STATISTIC(NumMemSetInfer, "Number of memsets inferred"); +STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy"); +STATISTIC(NumCpyToSet, "Number of memcpys converted to memset"); + +namespace { + +/// Represents a range of memset'd bytes with the ByteVal value. +/// This allows us to analyze stores like: +/// store 0 -> P+1 +/// store 0 -> P+0 +/// store 0 -> P+3 +/// store 0 -> P+2 +/// which sometimes happens with stores to arrays of structs etc. When we see +/// the first store, we make a range [1, 2). The second store extends the range +/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the +/// two ranges into [0, 3) which is memset'able. +struct MemsetRange { + // Start/End - A semi range that describes the span that this range covers. + // The range is closed at the start and open at the end: [Start, End). + int64_t Start, End; + + /// StartPtr - The getelementptr instruction that points to the start of the + /// range. + Value *StartPtr; + + /// Alignment - The known alignment of the first store. + unsigned Alignment; + + /// TheStores - The actual stores that make up this range. + SmallVector<Instruction*, 16> TheStores; + + bool isProfitableToUseMemset(const DataLayout &DL) const; +}; + +} // end anonymous namespace + +bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const { + // If we found more than 4 stores to merge or 16 bytes, use memset. + if (TheStores.size() >= 4 || End-Start >= 16) return true; + + // If there is nothing to merge, don't do anything. + if (TheStores.size() < 2) return false; + + // If any of the stores are a memset, then it is always good to extend the + // memset. + for (Instruction *SI : TheStores) + if (!isa<StoreInst>(SI)) + return true; + + // Assume that the code generator is capable of merging pairs of stores + // together if it wants to. + if (TheStores.size() == 2) return false; + + // If we have fewer than 8 stores, it can still be worthwhile to do this. + // For example, merging 4 i8 stores into an i32 store is useful almost always. + // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the + // memset will be split into 2 32-bit stores anyway) and doing so can + // pessimize the llvm optimizer. + // + // Since we don't have perfect knowledge here, make some assumptions: assume + // the maximum GPR width is the same size as the largest legal integer + // size. If so, check to see whether we will end up actually reducing the + // number of stores used. + unsigned Bytes = unsigned(End-Start); + unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8; + if (MaxIntSize == 0) + MaxIntSize = 1; + unsigned NumPointerStores = Bytes / MaxIntSize; + + // Assume the remaining bytes if any are done a byte at a time. + unsigned NumByteStores = Bytes % MaxIntSize; + + // If we will reduce the # stores (according to this heuristic), do the + // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32 + // etc. + return TheStores.size() > NumPointerStores+NumByteStores; +} + +namespace { + +class MemsetRanges { + using range_iterator = SmallVectorImpl<MemsetRange>::iterator; + + /// A sorted list of the memset ranges. + SmallVector<MemsetRange, 8> Ranges; + + const DataLayout &DL; + +public: + MemsetRanges(const DataLayout &DL) : DL(DL) {} + + using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator; + + const_iterator begin() const { return Ranges.begin(); } + const_iterator end() const { return Ranges.end(); } + bool empty() const { return Ranges.empty(); } + + void addInst(int64_t OffsetFromFirst, Instruction *Inst) { + if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) + addStore(OffsetFromFirst, SI); + else + addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst)); + } + + void addStore(int64_t OffsetFromFirst, StoreInst *SI) { + int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType()); + + addRange(OffsetFromFirst, StoreSize, + SI->getPointerOperand(), SI->getAlignment(), SI); + } + + void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) { + int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue(); + addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI); + } + + void addRange(int64_t Start, int64_t Size, Value *Ptr, + unsigned Alignment, Instruction *Inst); +}; + +} // end anonymous namespace + +/// Add a new store to the MemsetRanges data structure. This adds a +/// new range for the specified store at the specified offset, merging into +/// existing ranges as appropriate. +void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr, + unsigned Alignment, Instruction *Inst) { + int64_t End = Start+Size; + + range_iterator I = partition_point( + Ranges, [=](const MemsetRange &O) { return O.End < Start; }); + + // We now know that I == E, in which case we didn't find anything to merge + // with, or that Start <= I->End. If End < I->Start or I == E, then we need + // to insert a new range. Handle this now. + if (I == Ranges.end() || End < I->Start) { + MemsetRange &R = *Ranges.insert(I, MemsetRange()); + R.Start = Start; + R.End = End; + R.StartPtr = Ptr; + R.Alignment = Alignment; + R.TheStores.push_back(Inst); + return; + } + + // This store overlaps with I, add it. + I->TheStores.push_back(Inst); + + // At this point, we may have an interval that completely contains our store. + // If so, just add it to the interval and return. + if (I->Start <= Start && I->End >= End) + return; + + // Now we know that Start <= I->End and End >= I->Start so the range overlaps + // but is not entirely contained within the range. + + // See if the range extends the start of the range. In this case, it couldn't + // possibly cause it to join the prior range, because otherwise we would have + // stopped on *it*. + if (Start < I->Start) { + I->Start = Start; + I->StartPtr = Ptr; + I->Alignment = Alignment; + } + + // Now we know that Start <= I->End and Start >= I->Start (so the startpoint + // is in or right at the end of I), and that End >= I->Start. Extend I out to + // End. + if (End > I->End) { + I->End = End; + range_iterator NextI = I; + while (++NextI != Ranges.end() && End >= NextI->Start) { + // Merge the range in. + I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end()); + if (NextI->End > I->End) + I->End = NextI->End; + Ranges.erase(NextI); + NextI = I; + } + } +} + +//===----------------------------------------------------------------------===// +// MemCpyOptLegacyPass Pass +//===----------------------------------------------------------------------===// + +namespace { + +class MemCpyOptLegacyPass : public FunctionPass { + MemCpyOptPass Impl; + +public: + static char ID; // Pass identification, replacement for typeid + + MemCpyOptLegacyPass() : FunctionPass(ID) { + initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry()); + } + + bool runOnFunction(Function &F) override; + +private: + // This transformation requires dominator postdominator info + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<MemoryDependenceWrapperPass>(); + AU.addRequired<AAResultsWrapperPass>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addPreserved<GlobalsAAWrapperPass>(); + AU.addPreserved<MemoryDependenceWrapperPass>(); + } +}; + +} // end anonymous namespace + +char MemCpyOptLegacyPass::ID = 0; + +/// The public interface to this file... +FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); } + +INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization", + false, false) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass) +INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization", + false, false) + +/// When scanning forward over instructions, we look for some other patterns to +/// fold away. In particular, this looks for stores to neighboring locations of +/// memory. If it sees enough consecutive ones, it attempts to merge them +/// together into a memcpy/memset. +Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst, + Value *StartPtr, + Value *ByteVal) { + const DataLayout &DL = StartInst->getModule()->getDataLayout(); + + // Okay, so we now have a single store that can be splatable. Scan to find + // all subsequent stores of the same value to offset from the same pointer. + // Join these together into ranges, so we can decide whether contiguous blocks + // are stored. + MemsetRanges Ranges(DL); + + BasicBlock::iterator BI(StartInst); + for (++BI; !BI->isTerminator(); ++BI) { + if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) { + // If the instruction is readnone, ignore it, otherwise bail out. We + // don't even allow readonly here because we don't want something like: + // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A). + if (BI->mayWriteToMemory() || BI->mayReadFromMemory()) + break; + continue; + } + + if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) { + // If this is a store, see if we can merge it in. + if (!NextStore->isSimple()) break; + + // Check to see if this stored value is of the same byte-splattable value. + Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL); + if (isa<UndefValue>(ByteVal) && StoredByte) + ByteVal = StoredByte; + if (ByteVal != StoredByte) + break; + + // Check to see if this store is to a constant offset from the start ptr. + Optional<int64_t> Offset = + isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL); + if (!Offset) + break; + + Ranges.addStore(*Offset, NextStore); + } else { + MemSetInst *MSI = cast<MemSetInst>(BI); + + if (MSI->isVolatile() || ByteVal != MSI->getValue() || + !isa<ConstantInt>(MSI->getLength())) + break; + + // Check to see if this store is to a constant offset from the start ptr. + Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL); + if (!Offset) + break; + + Ranges.addMemSet(*Offset, MSI); + } + } + + // If we have no ranges, then we just had a single store with nothing that + // could be merged in. This is a very common case of course. + if (Ranges.empty()) + return nullptr; + + // If we had at least one store that could be merged in, add the starting + // store as well. We try to avoid this unless there is at least something + // interesting as a small compile-time optimization. + Ranges.addInst(0, StartInst); + + // If we create any memsets, we put it right before the first instruction that + // isn't part of the memset block. This ensure that the memset is dominated + // by any addressing instruction needed by the start of the block. + IRBuilder<> Builder(&*BI); + + // Now that we have full information about ranges, loop over the ranges and + // emit memset's for anything big enough to be worthwhile. + Instruction *AMemSet = nullptr; + for (const MemsetRange &Range : Ranges) { + if (Range.TheStores.size() == 1) continue; + + // If it is profitable to lower this range to memset, do so now. + if (!Range.isProfitableToUseMemset(DL)) + continue; + + // Otherwise, we do want to transform this! Create a new memset. + // Get the starting pointer of the block. + StartPtr = Range.StartPtr; + + // Determine alignment + unsigned Alignment = Range.Alignment; + if (Alignment == 0) { + Type *EltType = + cast<PointerType>(StartPtr->getType())->getElementType(); + Alignment = DL.getABITypeAlignment(EltType); + } + + AMemSet = + Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment); + + LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI + : Range.TheStores) dbgs() + << *SI << '\n'; + dbgs() << "With: " << *AMemSet << '\n'); + + if (!Range.TheStores.empty()) + AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc()); + + // Zap all the stores. + for (Instruction *SI : Range.TheStores) { + MD->removeInstruction(SI); + SI->eraseFromParent(); + } + ++NumMemSetInfer; + } + + return AMemSet; +} + +static unsigned findStoreAlignment(const DataLayout &DL, const StoreInst *SI) { + unsigned StoreAlign = SI->getAlignment(); + if (!StoreAlign) + StoreAlign = DL.getABITypeAlignment(SI->getOperand(0)->getType()); + return StoreAlign; +} + +static unsigned findLoadAlignment(const DataLayout &DL, const LoadInst *LI) { + unsigned LoadAlign = LI->getAlignment(); + if (!LoadAlign) + LoadAlign = DL.getABITypeAlignment(LI->getType()); + return LoadAlign; +} + +static unsigned findCommonAlignment(const DataLayout &DL, const StoreInst *SI, + const LoadInst *LI) { + unsigned StoreAlign = findStoreAlignment(DL, SI); + unsigned LoadAlign = findLoadAlignment(DL, LI); + return MinAlign(StoreAlign, LoadAlign); +} + +// This method try to lift a store instruction before position P. +// It will lift the store and its argument + that anything that +// may alias with these. +// The method returns true if it was successful. +static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P, + const LoadInst *LI) { + // If the store alias this position, early bail out. + MemoryLocation StoreLoc = MemoryLocation::get(SI); + if (isModOrRefSet(AA.getModRefInfo(P, StoreLoc))) + return false; + + // Keep track of the arguments of all instruction we plan to lift + // so we can make sure to lift them as well if appropriate. + DenseSet<Instruction*> Args; + if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand())) + if (Ptr->getParent() == SI->getParent()) + Args.insert(Ptr); + + // Instruction to lift before P. + SmallVector<Instruction*, 8> ToLift; + + // Memory locations of lifted instructions. + SmallVector<MemoryLocation, 8> MemLocs{StoreLoc}; + + // Lifted calls. + SmallVector<const CallBase *, 8> Calls; + + const MemoryLocation LoadLoc = MemoryLocation::get(LI); + + for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) { + auto *C = &*I; + + bool MayAlias = isModOrRefSet(AA.getModRefInfo(C, None)); + + bool NeedLift = false; + if (Args.erase(C)) + NeedLift = true; + else if (MayAlias) { + NeedLift = llvm::any_of(MemLocs, [C, &AA](const MemoryLocation &ML) { + return isModOrRefSet(AA.getModRefInfo(C, ML)); + }); + + if (!NeedLift) + NeedLift = llvm::any_of(Calls, [C, &AA](const CallBase *Call) { + return isModOrRefSet(AA.getModRefInfo(C, Call)); + }); + } + + if (!NeedLift) + continue; + + if (MayAlias) { + // Since LI is implicitly moved downwards past the lifted instructions, + // none of them may modify its source. + if (isModSet(AA.getModRefInfo(C, LoadLoc))) + return false; + else if (const auto *Call = dyn_cast<CallBase>(C)) { + // If we can't lift this before P, it's game over. + if (isModOrRefSet(AA.getModRefInfo(P, Call))) + return false; + + Calls.push_back(Call); + } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) { + // If we can't lift this before P, it's game over. + auto ML = MemoryLocation::get(C); + if (isModOrRefSet(AA.getModRefInfo(P, ML))) + return false; + + MemLocs.push_back(ML); + } else + // We don't know how to lift this instruction. + return false; + } + + ToLift.push_back(C); + for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k) + if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) { + if (A->getParent() == SI->getParent()) { + // Cannot hoist user of P above P + if(A == P) return false; + Args.insert(A); + } + } + } + + // We made it, we need to lift + for (auto *I : llvm::reverse(ToLift)) { + LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n"); + I->moveBefore(P); + } + + return true; +} + +bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) { + if (!SI->isSimple()) return false; + + // Avoid merging nontemporal stores since the resulting + // memcpy/memset would not be able to preserve the nontemporal hint. + // In theory we could teach how to propagate the !nontemporal metadata to + // memset calls. However, that change would force the backend to + // conservatively expand !nontemporal memset calls back to sequences of + // store instructions (effectively undoing the merging). + if (SI->getMetadata(LLVMContext::MD_nontemporal)) + return false; + + const DataLayout &DL = SI->getModule()->getDataLayout(); + + // Load to store forwarding can be interpreted as memcpy. + if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) { + if (LI->isSimple() && LI->hasOneUse() && + LI->getParent() == SI->getParent()) { + + auto *T = LI->getType(); + if (T->isAggregateType()) { + AliasAnalysis &AA = LookupAliasAnalysis(); + MemoryLocation LoadLoc = MemoryLocation::get(LI); + + // We use alias analysis to check if an instruction may store to + // the memory we load from in between the load and the store. If + // such an instruction is found, we try to promote there instead + // of at the store position. + Instruction *P = SI; + for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) { + if (isModSet(AA.getModRefInfo(&I, LoadLoc))) { + P = &I; + break; + } + } + + // We found an instruction that may write to the loaded memory. + // We can try to promote at this position instead of the store + // position if nothing alias the store memory after this and the store + // destination is not in the range. + if (P && P != SI) { + if (!moveUp(AA, SI, P, LI)) + P = nullptr; + } + + // If a valid insertion position is found, then we can promote + // the load/store pair to a memcpy. + if (P) { + // If we load from memory that may alias the memory we store to, + // memmove must be used to preserve semantic. If not, memcpy can + // be used. + bool UseMemMove = false; + if (!AA.isNoAlias(MemoryLocation::get(SI), LoadLoc)) + UseMemMove = true; + + uint64_t Size = DL.getTypeStoreSize(T); + + IRBuilder<> Builder(P); + Instruction *M; + if (UseMemMove) + M = Builder.CreateMemMove( + SI->getPointerOperand(), findStoreAlignment(DL, SI), + LI->getPointerOperand(), findLoadAlignment(DL, LI), Size); + else + M = Builder.CreateMemCpy( + SI->getPointerOperand(), findStoreAlignment(DL, SI), + LI->getPointerOperand(), findLoadAlignment(DL, LI), Size); + + LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => " + << *M << "\n"); + + MD->removeInstruction(SI); + SI->eraseFromParent(); + MD->removeInstruction(LI); + LI->eraseFromParent(); + ++NumMemCpyInstr; + + // Make sure we do not invalidate the iterator. + BBI = M->getIterator(); + return true; + } + } + + // Detect cases where we're performing call slot forwarding, but + // happen to be using a load-store pair to implement it, rather than + // a memcpy. + MemDepResult ldep = MD->getDependency(LI); + CallInst *C = nullptr; + if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst())) + C = dyn_cast<CallInst>(ldep.getInst()); + + if (C) { + // Check that nothing touches the dest of the "copy" between + // the call and the store. + Value *CpyDest = SI->getPointerOperand()->stripPointerCasts(); + bool CpyDestIsLocal = isa<AllocaInst>(CpyDest); + AliasAnalysis &AA = LookupAliasAnalysis(); + MemoryLocation StoreLoc = MemoryLocation::get(SI); + for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator(); + I != E; --I) { + if (isModOrRefSet(AA.getModRefInfo(&*I, StoreLoc))) { + C = nullptr; + break; + } + // The store to dest may never happen if an exception can be thrown + // between the load and the store. + if (I->mayThrow() && !CpyDestIsLocal) { + C = nullptr; + break; + } + } + } + + if (C) { + bool changed = performCallSlotOptzn( + LI, SI->getPointerOperand()->stripPointerCasts(), + LI->getPointerOperand()->stripPointerCasts(), + DL.getTypeStoreSize(SI->getOperand(0)->getType()), + findCommonAlignment(DL, SI, LI), C); + if (changed) { + MD->removeInstruction(SI); + SI->eraseFromParent(); + MD->removeInstruction(LI); + LI->eraseFromParent(); + ++NumMemCpyInstr; + return true; + } + } + } + } + + // There are two cases that are interesting for this code to handle: memcpy + // and memset. Right now we only handle memset. + + // Ensure that the value being stored is something that can be memset'able a + // byte at a time like "0" or "-1" or any width, as well as things like + // 0xA0A0A0A0 and 0.0. + auto *V = SI->getOperand(0); + if (Value *ByteVal = isBytewiseValue(V, DL)) { + if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(), + ByteVal)) { + BBI = I->getIterator(); // Don't invalidate iterator. + return true; + } + + // If we have an aggregate, we try to promote it to memset regardless + // of opportunity for merging as it can expose optimization opportunities + // in subsequent passes. + auto *T = V->getType(); + if (T->isAggregateType()) { + uint64_t Size = DL.getTypeStoreSize(T); + unsigned Align = SI->getAlignment(); + if (!Align) + Align = DL.getABITypeAlignment(T); + IRBuilder<> Builder(SI); + auto *M = + Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size, Align); + + LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n"); + + MD->removeInstruction(SI); + SI->eraseFromParent(); + NumMemSetInfer++; + + // Make sure we do not invalidate the iterator. + BBI = M->getIterator(); + return true; + } + } + + return false; +} + +bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) { + // See if there is another memset or store neighboring this memset which + // allows us to widen out the memset to do a single larger store. + if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile()) + if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(), + MSI->getValue())) { + BBI = I->getIterator(); // Don't invalidate iterator. + return true; + } + return false; +} + +/// Takes a memcpy and a call that it depends on, +/// and checks for the possibility of a call slot optimization by having +/// the call write its result directly into the destination of the memcpy. +bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpy, Value *cpyDest, + Value *cpySrc, uint64_t cpyLen, + unsigned cpyAlign, CallInst *C) { + // The general transformation to keep in mind is + // + // call @func(..., src, ...) + // memcpy(dest, src, ...) + // + // -> + // + // memcpy(dest, src, ...) + // call @func(..., dest, ...) + // + // Since moving the memcpy is technically awkward, we additionally check that + // src only holds uninitialized values at the moment of the call, meaning that + // the memcpy can be discarded rather than moved. + + // Lifetime marks shouldn't be operated on. + if (Function *F = C->getCalledFunction()) + if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start) + return false; + + // Deliberately get the source and destination with bitcasts stripped away, + // because we'll need to do type comparisons based on the underlying type. + CallSite CS(C); + + // Require that src be an alloca. This simplifies the reasoning considerably. + AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc); + if (!srcAlloca) + return false; + + ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); + if (!srcArraySize) + return false; + + const DataLayout &DL = cpy->getModule()->getDataLayout(); + uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) * + srcArraySize->getZExtValue(); + + if (cpyLen < srcSize) + return false; + + // Check that accessing the first srcSize bytes of dest will not cause a + // trap. Otherwise the transform is invalid since it might cause a trap + // to occur earlier than it otherwise would. + if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) { + // The destination is an alloca. Check it is larger than srcSize. + ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize()); + if (!destArraySize) + return false; + + uint64_t destSize = DL.getTypeAllocSize(A->getAllocatedType()) * + destArraySize->getZExtValue(); + + if (destSize < srcSize) + return false; + } else if (Argument *A = dyn_cast<Argument>(cpyDest)) { + // The store to dest may never happen if the call can throw. + if (C->mayThrow()) + return false; + + if (A->getDereferenceableBytes() < srcSize) { + // If the destination is an sret parameter then only accesses that are + // outside of the returned struct type can trap. + if (!A->hasStructRetAttr()) + return false; + + Type *StructTy = cast<PointerType>(A->getType())->getElementType(); + if (!StructTy->isSized()) { + // The call may never return and hence the copy-instruction may never + // be executed, and therefore it's not safe to say "the destination + // has at least <cpyLen> bytes, as implied by the copy-instruction", + return false; + } + + uint64_t destSize = DL.getTypeAllocSize(StructTy); + if (destSize < srcSize) + return false; + } + } else { + return false; + } + + // Check that dest points to memory that is at least as aligned as src. + unsigned srcAlign = srcAlloca->getAlignment(); + if (!srcAlign) + srcAlign = DL.getABITypeAlignment(srcAlloca->getAllocatedType()); + bool isDestSufficientlyAligned = srcAlign <= cpyAlign; + // If dest is not aligned enough and we can't increase its alignment then + // bail out. + if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest)) + return false; + + // Check that src is not accessed except via the call and the memcpy. This + // guarantees that it holds only undefined values when passed in (so the final + // memcpy can be dropped), that it is not read or written between the call and + // the memcpy, and that writing beyond the end of it is undefined. + SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(), + srcAlloca->user_end()); + while (!srcUseList.empty()) { + User *U = srcUseList.pop_back_val(); + + if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) { + for (User *UU : U->users()) + srcUseList.push_back(UU); + continue; + } + if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) { + if (!G->hasAllZeroIndices()) + return false; + + for (User *UU : U->users()) + srcUseList.push_back(UU); + continue; + } + if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U)) + if (IT->isLifetimeStartOrEnd()) + continue; + + if (U != C && U != cpy) + return false; + } + + // Check that src isn't captured by the called function since the + // transformation can cause aliasing issues in that case. + for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) + if (CS.getArgument(i) == cpySrc && !CS.doesNotCapture(i)) + return false; + + // Since we're changing the parameter to the callsite, we need to make sure + // that what would be the new parameter dominates the callsite. + DominatorTree &DT = LookupDomTree(); + if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest)) + if (!DT.dominates(cpyDestInst, C)) + return false; + + // In addition to knowing that the call does not access src in some + // unexpected manner, for example via a global, which we deduce from + // the use analysis, we also need to know that it does not sneakily + // access dest. We rely on AA to figure this out for us. + AliasAnalysis &AA = LookupAliasAnalysis(); + ModRefInfo MR = AA.getModRefInfo(C, cpyDest, LocationSize::precise(srcSize)); + // If necessary, perform additional analysis. + if (isModOrRefSet(MR)) + MR = AA.callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), &DT); + if (isModOrRefSet(MR)) + return false; + + // We can't create address space casts here because we don't know if they're + // safe for the target. + if (cpySrc->getType()->getPointerAddressSpace() != + cpyDest->getType()->getPointerAddressSpace()) + return false; + for (unsigned i = 0; i < CS.arg_size(); ++i) + if (CS.getArgument(i)->stripPointerCasts() == cpySrc && + cpySrc->getType()->getPointerAddressSpace() != + CS.getArgument(i)->getType()->getPointerAddressSpace()) + return false; + + // All the checks have passed, so do the transformation. + bool changedArgument = false; + for (unsigned i = 0; i < CS.arg_size(); ++i) + if (CS.getArgument(i)->stripPointerCasts() == cpySrc) { + Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest + : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(), + cpyDest->getName(), C); + changedArgument = true; + if (CS.getArgument(i)->getType() == Dest->getType()) + CS.setArgument(i, Dest); + else + CS.setArgument(i, CastInst::CreatePointerCast(Dest, + CS.getArgument(i)->getType(), Dest->getName(), C)); + } + + if (!changedArgument) + return false; + + // If the destination wasn't sufficiently aligned then increase its alignment. + if (!isDestSufficientlyAligned) { + assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!"); + cast<AllocaInst>(cpyDest)->setAlignment(MaybeAlign(srcAlign)); + } + + // Drop any cached information about the call, because we may have changed + // its dependence information by changing its parameter. + MD->removeInstruction(C); + + // Update AA metadata + // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be + // handled here, but combineMetadata doesn't support them yet + unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, + LLVMContext::MD_noalias, + LLVMContext::MD_invariant_group, + LLVMContext::MD_access_group}; + combineMetadata(C, cpy, KnownIDs, true); + + // Remove the memcpy. + MD->removeInstruction(cpy); + ++NumMemCpyInstr; + + return true; +} + +/// We've found that the (upward scanning) memory dependence of memcpy 'M' is +/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can. +bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M, + MemCpyInst *MDep) { + // We can only transforms memcpy's where the dest of one is the source of the + // other. + if (M->getSource() != MDep->getDest() || MDep->isVolatile()) + return false; + + // If dep instruction is reading from our current input, then it is a noop + // transfer and substituting the input won't change this instruction. Just + // ignore the input and let someone else zap MDep. This handles cases like: + // memcpy(a <- a) + // memcpy(b <- a) + if (M->getSource() == MDep->getSource()) + return false; + + // Second, the length of the memcpy's must be the same, or the preceding one + // must be larger than the following one. + ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength()); + ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength()); + if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue()) + return false; + + AliasAnalysis &AA = LookupAliasAnalysis(); + + // Verify that the copied-from memory doesn't change in between the two + // transfers. For example, in: + // memcpy(a <- b) + // *b = 42; + // memcpy(c <- a) + // It would be invalid to transform the second memcpy into memcpy(c <- b). + // + // TODO: If the code between M and MDep is transparent to the destination "c", + // then we could still perform the xform by moving M up to the first memcpy. + // + // NOTE: This is conservative, it will stop on any read from the source loc, + // not just the defining memcpy. + MemDepResult SourceDep = + MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false, + M->getIterator(), M->getParent()); + if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) + return false; + + // If the dest of the second might alias the source of the first, then the + // source and dest might overlap. We still want to eliminate the intermediate + // value, but we have to generate a memmove instead of memcpy. + bool UseMemMove = false; + if (!AA.isNoAlias(MemoryLocation::getForDest(M), + MemoryLocation::getForSource(MDep))) + UseMemMove = true; + + // If all checks passed, then we can transform M. + LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n" + << *MDep << '\n' << *M << '\n'); + + // TODO: Is this worth it if we're creating a less aligned memcpy? For + // example we could be moving from movaps -> movq on x86. + IRBuilder<> Builder(M); + if (UseMemMove) + Builder.CreateMemMove(M->getRawDest(), M->getDestAlignment(), + MDep->getRawSource(), MDep->getSourceAlignment(), + M->getLength(), M->isVolatile()); + else + Builder.CreateMemCpy(M->getRawDest(), M->getDestAlignment(), + MDep->getRawSource(), MDep->getSourceAlignment(), + M->getLength(), M->isVolatile()); + + // Remove the instruction we're replacing. + MD->removeInstruction(M); + M->eraseFromParent(); + ++NumMemCpyInstr; + return true; +} + +/// We've found that the (upward scanning) memory dependence of \p MemCpy is +/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that +/// weren't copied over by \p MemCpy. +/// +/// In other words, transform: +/// \code +/// memset(dst, c, dst_size); +/// memcpy(dst, src, src_size); +/// \endcode +/// into: +/// \code +/// memcpy(dst, src, src_size); +/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size); +/// \endcode +bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy, + MemSetInst *MemSet) { + // We can only transform memset/memcpy with the same destination. + if (MemSet->getDest() != MemCpy->getDest()) + return false; + + // Check that there are no other dependencies on the memset destination. + MemDepResult DstDepInfo = + MD->getPointerDependencyFrom(MemoryLocation::getForDest(MemSet), false, + MemCpy->getIterator(), MemCpy->getParent()); + if (DstDepInfo.getInst() != MemSet) + return false; + + // Use the same i8* dest as the memcpy, killing the memset dest if different. + Value *Dest = MemCpy->getRawDest(); + Value *DestSize = MemSet->getLength(); + Value *SrcSize = MemCpy->getLength(); + + // By default, create an unaligned memset. + unsigned Align = 1; + // If Dest is aligned, and SrcSize is constant, use the minimum alignment + // of the sum. + const unsigned DestAlign = + std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment()); + if (DestAlign > 1) + if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize)) + Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign); + + IRBuilder<> Builder(MemCpy); + + // If the sizes have different types, zext the smaller one. + if (DestSize->getType() != SrcSize->getType()) { + if (DestSize->getType()->getIntegerBitWidth() > + SrcSize->getType()->getIntegerBitWidth()) + SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType()); + else + DestSize = Builder.CreateZExt(DestSize, SrcSize->getType()); + } + + Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize); + Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize); + Value *MemsetLen = Builder.CreateSelect( + Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff); + Builder.CreateMemSet( + Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest, + SrcSize), + MemSet->getOperand(1), MemsetLen, Align); + + MD->removeInstruction(MemSet); + MemSet->eraseFromParent(); + return true; +} + +/// Determine whether the instruction has undefined content for the given Size, +/// either because it was freshly alloca'd or started its lifetime. +static bool hasUndefContents(Instruction *I, ConstantInt *Size) { + if (isa<AllocaInst>(I)) + return true; + + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) + if (II->getIntrinsicID() == Intrinsic::lifetime_start) + if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0))) + if (LTSize->getZExtValue() >= Size->getZExtValue()) + return true; + + return false; +} + +/// Transform memcpy to memset when its source was just memset. +/// In other words, turn: +/// \code +/// memset(dst1, c, dst1_size); +/// memcpy(dst2, dst1, dst2_size); +/// \endcode +/// into: +/// \code +/// memset(dst1, c, dst1_size); +/// memset(dst2, c, dst2_size); +/// \endcode +/// When dst2_size <= dst1_size. +/// +/// The \p MemCpy must have a Constant length. +bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy, + MemSetInst *MemSet) { + AliasAnalysis &AA = LookupAliasAnalysis(); + + // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and + // memcpying from the same address. Otherwise it is hard to reason about. + if (!AA.isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource())) + return false; + + // A known memset size is required. + ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength()); + if (!MemSetSize) + return false; + + // Make sure the memcpy doesn't read any more than what the memset wrote. + // Don't worry about sizes larger than i64. + ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength()); + if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) { + // If the memcpy is larger than the memset, but the memory was undef prior + // to the memset, we can just ignore the tail. Technically we're only + // interested in the bytes from MemSetSize..CopySize here, but as we can't + // easily represent this location, we use the full 0..CopySize range. + MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy); + MemDepResult DepInfo = MD->getPointerDependencyFrom( + MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent()); + if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize)) + CopySize = MemSetSize; + else + return false; + } + + IRBuilder<> Builder(MemCpy); + Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1), + CopySize, MemCpy->getDestAlignment()); + return true; +} + +/// Perform simplification of memcpy's. If we have memcpy A +/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite +/// B to be a memcpy from X to Z (or potentially a memmove, depending on +/// circumstances). This allows later passes to remove the first memcpy +/// altogether. +bool MemCpyOptPass::processMemCpy(MemCpyInst *M) { + // We can only optimize non-volatile memcpy's. + if (M->isVolatile()) return false; + + // If the source and destination of the memcpy are the same, then zap it. + if (M->getSource() == M->getDest()) { + MD->removeInstruction(M); + M->eraseFromParent(); + return false; + } + + // If copying from a constant, try to turn the memcpy into a memset. + if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource())) + if (GV->isConstant() && GV->hasDefinitiveInitializer()) + if (Value *ByteVal = isBytewiseValue(GV->getInitializer(), + M->getModule()->getDataLayout())) { + IRBuilder<> Builder(M); + Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(), + M->getDestAlignment(), false); + MD->removeInstruction(M); + M->eraseFromParent(); + ++NumCpyToSet; + return true; + } + + MemDepResult DepInfo = MD->getDependency(M); + + // Try to turn a partially redundant memset + memcpy into + // memcpy + smaller memset. We don't need the memcpy size for this. + if (DepInfo.isClobber()) + if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst())) + if (processMemSetMemCpyDependence(M, MDep)) + return true; + + // The optimizations after this point require the memcpy size. + ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength()); + if (!CopySize) return false; + + // There are four possible optimizations we can do for memcpy: + // a) memcpy-memcpy xform which exposes redundance for DSE. + // b) call-memcpy xform for return slot optimization. + // c) memcpy from freshly alloca'd space or space that has just started its + // lifetime copies undefined data, and we can therefore eliminate the + // memcpy in favor of the data that was already at the destination. + // d) memcpy from a just-memset'd source can be turned into memset. + if (DepInfo.isClobber()) { + if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) { + // FIXME: Can we pass in either of dest/src alignment here instead + // of conservatively taking the minimum? + unsigned Align = MinAlign(M->getDestAlignment(), M->getSourceAlignment()); + if (performCallSlotOptzn(M, M->getDest(), M->getSource(), + CopySize->getZExtValue(), Align, + C)) { + MD->removeInstruction(M); + M->eraseFromParent(); + return true; + } + } + } + + MemoryLocation SrcLoc = MemoryLocation::getForSource(M); + MemDepResult SrcDepInfo = MD->getPointerDependencyFrom( + SrcLoc, true, M->getIterator(), M->getParent()); + + if (SrcDepInfo.isClobber()) { + if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst())) + return processMemCpyMemCpyDependence(M, MDep); + } else if (SrcDepInfo.isDef()) { + if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) { + MD->removeInstruction(M); + M->eraseFromParent(); + ++NumMemCpyInstr; + return true; + } + } + + if (SrcDepInfo.isClobber()) + if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst())) + if (performMemCpyToMemSetOptzn(M, MDep)) { + MD->removeInstruction(M); + M->eraseFromParent(); + ++NumCpyToSet; + return true; + } + + return false; +} + +/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed +/// not to alias. +bool MemCpyOptPass::processMemMove(MemMoveInst *M) { + AliasAnalysis &AA = LookupAliasAnalysis(); + + if (!TLI->has(LibFunc_memmove)) + return false; + + // See if the pointers alias. + if (!AA.isNoAlias(MemoryLocation::getForDest(M), + MemoryLocation::getForSource(M))) + return false; + + LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M + << "\n"); + + // If not, then we know we can transform this. + Type *ArgTys[3] = { M->getRawDest()->getType(), + M->getRawSource()->getType(), + M->getLength()->getType() }; + M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(), + Intrinsic::memcpy, ArgTys)); + + // MemDep may have over conservative information about this instruction, just + // conservatively flush it from the cache. + MD->removeInstruction(M); + + ++NumMoveToCpy; + return true; +} + +/// This is called on every byval argument in call sites. +bool MemCpyOptPass::processByValArgument(CallSite CS, unsigned ArgNo) { + const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout(); + // Find out what feeds this byval argument. + Value *ByValArg = CS.getArgument(ArgNo); + Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType(); + uint64_t ByValSize = DL.getTypeAllocSize(ByValTy); + MemDepResult DepInfo = MD->getPointerDependencyFrom( + MemoryLocation(ByValArg, LocationSize::precise(ByValSize)), true, + CS.getInstruction()->getIterator(), CS.getInstruction()->getParent()); + if (!DepInfo.isClobber()) + return false; + + // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by + // a memcpy, see if we can byval from the source of the memcpy instead of the + // result. + MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst()); + if (!MDep || MDep->isVolatile() || + ByValArg->stripPointerCasts() != MDep->getDest()) + return false; + + // The length of the memcpy must be larger or equal to the size of the byval. + ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength()); + if (!C1 || C1->getValue().getZExtValue() < ByValSize) + return false; + + // Get the alignment of the byval. If the call doesn't specify the alignment, + // then it is some target specific value that we can't know. + unsigned ByValAlign = CS.getParamAlignment(ArgNo); + if (ByValAlign == 0) return false; + + // If it is greater than the memcpy, then we check to see if we can force the + // source of the memcpy to the alignment we need. If we fail, we bail out. + AssumptionCache &AC = LookupAssumptionCache(); + DominatorTree &DT = LookupDomTree(); + if (MDep->getSourceAlignment() < ByValAlign && + getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, + CS.getInstruction(), &AC, &DT) < ByValAlign) + return false; + + // The address space of the memcpy source must match the byval argument + if (MDep->getSource()->getType()->getPointerAddressSpace() != + ByValArg->getType()->getPointerAddressSpace()) + return false; + + // Verify that the copied-from memory doesn't change in between the memcpy and + // the byval call. + // memcpy(a <- b) + // *b = 42; + // foo(*a) + // It would be invalid to transform the second memcpy into foo(*b). + // + // NOTE: This is conservative, it will stop on any read from the source loc, + // not just the defining memcpy. + MemDepResult SourceDep = MD->getPointerDependencyFrom( + MemoryLocation::getForSource(MDep), false, + CS.getInstruction()->getIterator(), MDep->getParent()); + if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) + return false; + + Value *TmpCast = MDep->getSource(); + if (MDep->getSource()->getType() != ByValArg->getType()) + TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(), + "tmpcast", CS.getInstruction()); + + LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n" + << " " << *MDep << "\n" + << " " << *CS.getInstruction() << "\n"); + + // Otherwise we're good! Update the byval argument. + CS.setArgument(ArgNo, TmpCast); + ++NumMemCpyInstr; + return true; +} + +/// Executes one iteration of MemCpyOptPass. +bool MemCpyOptPass::iterateOnFunction(Function &F) { + bool MadeChange = false; + + DominatorTree &DT = LookupDomTree(); + + // Walk all instruction in the function. + for (BasicBlock &BB : F) { + // Skip unreachable blocks. For example processStore assumes that an + // instruction in a BB can't be dominated by a later instruction in the + // same BB (which is a scenario that can happen for an unreachable BB that + // has itself as a predecessor). + if (!DT.isReachableFromEntry(&BB)) + continue; + + for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) { + // Avoid invalidating the iterator. + Instruction *I = &*BI++; + + bool RepeatInstruction = false; + + if (StoreInst *SI = dyn_cast<StoreInst>(I)) + MadeChange |= processStore(SI, BI); + else if (MemSetInst *M = dyn_cast<MemSetInst>(I)) + RepeatInstruction = processMemSet(M, BI); + else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I)) + RepeatInstruction = processMemCpy(M); + else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) + RepeatInstruction = processMemMove(M); + else if (auto CS = CallSite(I)) { + for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) + if (CS.isByValArgument(i)) + MadeChange |= processByValArgument(CS, i); + } + + // Reprocess the instruction if desired. + if (RepeatInstruction) { + if (BI != BB.begin()) + --BI; + MadeChange = true; + } + } + } + + return MadeChange; +} + +PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) { + auto &MD = AM.getResult<MemoryDependenceAnalysis>(F); + auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); + + auto LookupAliasAnalysis = [&]() -> AliasAnalysis & { + return AM.getResult<AAManager>(F); + }; + auto LookupAssumptionCache = [&]() -> AssumptionCache & { + return AM.getResult<AssumptionAnalysis>(F); + }; + auto LookupDomTree = [&]() -> DominatorTree & { + return AM.getResult<DominatorTreeAnalysis>(F); + }; + + bool MadeChange = runImpl(F, &MD, &TLI, LookupAliasAnalysis, + LookupAssumptionCache, LookupDomTree); + if (!MadeChange) + return PreservedAnalyses::all(); + + PreservedAnalyses PA; + PA.preserveSet<CFGAnalyses>(); + PA.preserve<GlobalsAA>(); + PA.preserve<MemoryDependenceAnalysis>(); + return PA; +} + +bool MemCpyOptPass::runImpl( + Function &F, MemoryDependenceResults *MD_, TargetLibraryInfo *TLI_, + std::function<AliasAnalysis &()> LookupAliasAnalysis_, + std::function<AssumptionCache &()> LookupAssumptionCache_, + std::function<DominatorTree &()> LookupDomTree_) { + bool MadeChange = false; + MD = MD_; + TLI = TLI_; + LookupAliasAnalysis = std::move(LookupAliasAnalysis_); + LookupAssumptionCache = std::move(LookupAssumptionCache_); + LookupDomTree = std::move(LookupDomTree_); + + // If we don't have at least memset and memcpy, there is little point of doing + // anything here. These are required by a freestanding implementation, so if + // even they are disabled, there is no point in trying hard. + if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy)) + return false; + + while (true) { + if (!iterateOnFunction(F)) + break; + MadeChange = true; + } + + MD = nullptr; + return MadeChange; +} + +/// This is the main transformation entry point for a function. +bool MemCpyOptLegacyPass::runOnFunction(Function &F) { + if (skipFunction(F)) + return false; + + auto *MD = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep(); + auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); + + auto LookupAliasAnalysis = [this]() -> AliasAnalysis & { + return getAnalysis<AAResultsWrapperPass>().getAAResults(); + }; + auto LookupAssumptionCache = [this, &F]() -> AssumptionCache & { + return getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); + }; + auto LookupDomTree = [this]() -> DominatorTree & { + return getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + }; + + return Impl.runImpl(F, MD, TLI, LookupAliasAnalysis, LookupAssumptionCache, + LookupDomTree); +} |