| //===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass performs various transformations related to eliminating memcpy |
| // calls, or transforming sets of stores into memset's. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "memcpyopt" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/GlobalVariable.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/MemoryDependenceAnalysis.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Support/IRBuilder.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Target/TargetLibraryInfo.h" |
| #include <list> |
| using namespace llvm; |
| |
| 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"); |
| |
| static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx, |
| bool &VariableIdxFound, const TargetData &TD){ |
| // Skip over the first indices. |
| gep_type_iterator GTI = gep_type_begin(GEP); |
| for (unsigned i = 1; i != Idx; ++i, ++GTI) |
| /*skip along*/; |
| |
| // Compute the offset implied by the rest of the indices. |
| int64_t Offset = 0; |
| for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) { |
| ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i)); |
| if (OpC == 0) |
| return VariableIdxFound = true; |
| if (OpC->isZero()) continue; // No offset. |
| |
| // Handle struct indices, which add their field offset to the pointer. |
| if (const StructType *STy = dyn_cast<StructType>(*GTI)) { |
| Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); |
| continue; |
| } |
| |
| // Otherwise, we have a sequential type like an array or vector. Multiply |
| // the index by the ElementSize. |
| uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); |
| Offset += Size*OpC->getSExtValue(); |
| } |
| |
| return Offset; |
| } |
| |
| /// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a |
| /// constant offset, and return that constant offset. For example, Ptr1 might |
| /// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8. |
| static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset, |
| const TargetData &TD) { |
| Ptr1 = Ptr1->stripPointerCasts(); |
| Ptr2 = Ptr2->stripPointerCasts(); |
| GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1); |
| GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2); |
| |
| bool VariableIdxFound = false; |
| |
| // If one pointer is a GEP and the other isn't, then see if the GEP is a |
| // constant offset from the base, as in "P" and "gep P, 1". |
| if (GEP1 && GEP2 == 0 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) { |
| Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, TD); |
| return !VariableIdxFound; |
| } |
| |
| if (GEP2 && GEP1 == 0 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) { |
| Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, TD); |
| return !VariableIdxFound; |
| } |
| |
| // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical |
| // base. After that base, they may have some number of common (and |
| // potentially variable) indices. After that they handle some constant |
| // offset, which determines their offset from each other. At this point, we |
| // handle no other case. |
| if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0)) |
| return false; |
| |
| // Skip any common indices and track the GEP types. |
| unsigned Idx = 1; |
| for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx) |
| if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx)) |
| break; |
| |
| int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD); |
| int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD); |
| if (VariableIdxFound) return false; |
| |
| Offset = Offset2-Offset1; |
| return true; |
| } |
| |
| |
| /// MemsetRange - 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. |
| namespace { |
| 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 TargetData &TD) const; |
| |
| }; |
| } // end anon namespace |
| |
| bool MemsetRange::isProfitableToUseMemset(const TargetData &TD) const { |
| // If we found more than 8 stores to merge or 64 bytes, use memset. |
| if (TheStores.size() >= 8 || End-Start >= 64) 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 (unsigned i = 0, e = TheStores.size(); i != e; ++i) |
| if (!isa<StoreInst>(TheStores[i])) |
| 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 pointer size and assume that |
| // this width can be stored. If so, check to see whether we will end up |
| // actually reducing the number of stores used. |
| unsigned Bytes = unsigned(End-Start); |
| unsigned NumPointerStores = Bytes/TD.getPointerSize(); |
| |
| // Assume the remaining bytes if any are done a byte at a time. |
| unsigned NumByteStores = Bytes - NumPointerStores*TD.getPointerSize(); |
| |
| // 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 { |
| /// Ranges - A sorted list of the memset ranges. We use std::list here |
| /// because each element is relatively large and expensive to copy. |
| std::list<MemsetRange> Ranges; |
| typedef std::list<MemsetRange>::iterator range_iterator; |
| const TargetData &TD; |
| public: |
| MemsetRanges(const TargetData &td) : TD(td) {} |
| |
| typedef std::list<MemsetRange>::const_iterator 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 = TD.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->getAlignment(), MSI); |
| } |
| |
| void addRange(int64_t Start, int64_t Size, Value *Ptr, |
| unsigned Alignment, Instruction *Inst); |
| |
| }; |
| |
| } // end anon namespace |
| |
| |
| /// addRange - 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. |
| /// |
| /// Do a linear search of the ranges to see if this can be joined and/or to |
| /// find the insertion point in the list. We keep the ranges sorted for |
| /// simplicity here. This is a linear search of a linked list, which is ugly, |
| /// however the number of ranges is limited, so this won't get crazy slow. |
| void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr, |
| unsigned Alignment, Instruction *Inst) { |
| int64_t End = Start+Size; |
| range_iterator I = Ranges.begin(), E = Ranges.end(); |
| |
| while (I != E && Start > I->End) |
| ++I; |
| |
| // 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 == E || 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 != E && 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; |
| } |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // MemCpyOpt Pass |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| class MemCpyOpt : public FunctionPass { |
| MemoryDependenceAnalysis *MD; |
| TargetLibraryInfo *TLI; |
| const TargetData *TD; |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| MemCpyOpt() : FunctionPass(ID) { |
| initializeMemCpyOptPass(*PassRegistry::getPassRegistry()); |
| MD = 0; |
| TLI = 0; |
| TD = 0; |
| } |
| |
| bool runOnFunction(Function &F); |
| |
| private: |
| // This transformation requires dominator postdominator info |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<MemoryDependenceAnalysis>(); |
| AU.addRequired<AliasAnalysis>(); |
| AU.addRequired<TargetLibraryInfo>(); |
| AU.addPreserved<AliasAnalysis>(); |
| AU.addPreserved<MemoryDependenceAnalysis>(); |
| } |
| |
| // Helper fuctions |
| bool processStore(StoreInst *SI, BasicBlock::iterator &BBI); |
| bool processMemSet(MemSetInst *SI, BasicBlock::iterator &BBI); |
| bool processMemCpy(MemCpyInst *M); |
| bool processMemMove(MemMoveInst *M); |
| bool performCallSlotOptzn(Instruction *cpy, Value *cpyDst, Value *cpySrc, |
| uint64_t cpyLen, CallInst *C); |
| bool processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep, |
| uint64_t MSize); |
| bool processByValArgument(CallSite CS, unsigned ArgNo); |
| Instruction *tryMergingIntoMemset(Instruction *I, Value *StartPtr, |
| Value *ByteVal); |
| |
| bool iterateOnFunction(Function &F); |
| }; |
| |
| char MemCpyOpt::ID = 0; |
| } |
| |
| // createMemCpyOptPass - The public interface to this file... |
| FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); } |
| |
| INITIALIZE_PASS_BEGIN(MemCpyOpt, "memcpyopt", "MemCpy Optimization", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTree) |
| INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) |
| INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) |
| INITIALIZE_AG_DEPENDENCY(AliasAnalysis) |
| INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization", |
| false, false) |
| |
| /// tryMergingIntoMemset - 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 *MemCpyOpt::tryMergingIntoMemset(Instruction *StartInst, |
| Value *StartPtr, Value *ByteVal) { |
| if (TD == 0) return 0; |
| |
| // 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(*TD); |
| |
| BasicBlock::iterator BI = StartInst; |
| for (++BI; !isa<TerminatorInst>(BI); ++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->isVolatile()) break; |
| |
| // Check to see if this stored value is of the same byte-splattable value. |
| if (ByteVal != isBytewiseValue(NextStore->getOperand(0))) |
| break; |
| |
| // Check to see if this store is to a constant offset from the start ptr. |
| int64_t Offset; |
| if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), |
| Offset, *TD)) |
| 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. |
| int64_t Offset; |
| if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, *TD)) |
| 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 0; |
| |
| // 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 = 0; |
| for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end(); |
| I != E; ++I) { |
| const MemsetRange &Range = *I; |
| |
| if (Range.TheStores.size() == 1) continue; |
| |
| // If it is profitable to lower this range to memset, do so now. |
| if (!Range.isProfitableToUseMemset(*TD)) |
| 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) { |
| const Type *EltType = |
| cast<PointerType>(StartPtr->getType())->getElementType(); |
| Alignment = TD->getABITypeAlignment(EltType); |
| } |
| |
| AMemSet = |
| Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment); |
| |
| DEBUG(dbgs() << "Replace stores:\n"; |
| for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i) |
| dbgs() << *Range.TheStores[i] << '\n'; |
| dbgs() << "With: " << *AMemSet << '\n'); |
| |
| if (!Range.TheStores.empty()) |
| AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc()); |
| |
| // Zap all the stores. |
| for (SmallVector<Instruction*, 16>::const_iterator |
| SI = Range.TheStores.begin(), |
| SE = Range.TheStores.end(); SI != SE; ++SI) { |
| MD->removeInstruction(*SI); |
| (*SI)->eraseFromParent(); |
| } |
| ++NumMemSetInfer; |
| } |
| |
| return AMemSet; |
| } |
| |
| |
| bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) { |
| if (SI->isVolatile()) return false; |
| |
| if (TD == 0) return false; |
| |
| // 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. |
| if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) { |
| if (!LI->isVolatile() && LI->hasOneUse() && |
| LI->getParent() == SI->getParent()) { |
| MemDepResult ldep = MD->getDependency(LI); |
| CallInst *C = 0; |
| 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. |
| AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); |
| AliasAnalysis::Location StoreLoc = AA.getLocation(SI); |
| for (BasicBlock::iterator I = --BasicBlock::iterator(SI), |
| E = C; I != E; --I) { |
| if (AA.getModRefInfo(&*I, StoreLoc) != AliasAnalysis::NoModRef) { |
| C = 0; |
| break; |
| } |
| } |
| } |
| |
| if (C) { |
| bool changed = performCallSlotOptzn(LI, |
| SI->getPointerOperand()->stripPointerCasts(), |
| LI->getPointerOperand()->stripPointerCasts(), |
| TD->getTypeStoreSize(SI->getOperand(0)->getType()), 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. |
| if (Value *ByteVal = isBytewiseValue(SI->getOperand(0))) |
| if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(), |
| ByteVal)) { |
| BBI = I; // Don't invalidate iterator. |
| return true; |
| } |
| |
| return false; |
| } |
| |
| bool MemCpyOpt::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; // Don't invalidate iterator. |
| return true; |
| } |
| return false; |
| } |
| |
| |
| /// performCallSlotOptzn - 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 MemCpyOpt::performCallSlotOptzn(Instruction *cpy, |
| Value *cpyDest, Value *cpySrc, |
| uint64_t cpyLen, 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. |
| |
| // 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; |
| |
| // Check that all of src is copied to dest. |
| if (TD == 0) return false; |
| |
| ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); |
| if (!srcArraySize) |
| return false; |
| |
| uint64_t srcSize = TD->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 = TD->getTypeAllocSize(A->getAllocatedType()) * |
| destArraySize->getZExtValue(); |
| |
| if (destSize < srcSize) |
| return false; |
| } else if (Argument *A = dyn_cast<Argument>(cpyDest)) { |
| // 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; |
| |
| const Type *StructTy = cast<PointerType>(A->getType())->getElementType(); |
| uint64_t destSize = TD->getTypeAllocSize(StructTy); |
| |
| if (destSize < srcSize) |
| return false; |
| } else { |
| 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->use_begin(), |
| srcAlloca->use_end()); |
| while (!srcUseList.empty()) { |
| User *UI = srcUseList.pop_back_val(); |
| |
| if (isa<BitCastInst>(UI)) { |
| for (User::use_iterator I = UI->use_begin(), E = UI->use_end(); |
| I != E; ++I) |
| srcUseList.push_back(*I); |
| } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(UI)) { |
| if (G->hasAllZeroIndices()) |
| for (User::use_iterator I = UI->use_begin(), E = UI->use_end(); |
| I != E; ++I) |
| srcUseList.push_back(*I); |
| else |
| return false; |
| } else if (UI != C && UI != cpy) { |
| 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 = getAnalysis<DominatorTree>(); |
| 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 = getAnalysis<AliasAnalysis>(); |
| if (AA.getModRefInfo(C, cpyDest, srcSize) != AliasAnalysis::NoModRef) |
| 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) { |
| if (cpySrc->getType() != cpyDest->getType()) |
| cpyDest = CastInst::CreatePointerCast(cpyDest, cpySrc->getType(), |
| cpyDest->getName(), C); |
| changedArgument = true; |
| if (CS.getArgument(i)->getType() == cpyDest->getType()) |
| CS.setArgument(i, cpyDest); |
| else |
| CS.setArgument(i, CastInst::CreatePointerCast(cpyDest, |
| CS.getArgument(i)->getType(), cpyDest->getName(), C)); |
| } |
| |
| if (!changedArgument) |
| return false; |
| |
| // Drop any cached information about the call, because we may have changed |
| // its dependence information by changing its parameter. |
| MD->removeInstruction(C); |
| |
| // Remove the memcpy. |
| MD->removeInstruction(cpy); |
| ++NumMemCpyInstr; |
| |
| return true; |
| } |
| |
| /// processMemCpyMemCpyDependence - 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. MSize is the size of M's copy. |
| /// |
| bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep, |
| uint64_t MSize) { |
| // 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 = getAnalysis<AliasAnalysis>(); |
| |
| // 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(AA.getLocationForSource(MDep), |
| false, M, 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(AA.getLocationForDest(M), AA.getLocationForSource(MDep))) |
| UseMemMove = true; |
| |
| // If all checks passed, then we can transform M. |
| |
| // Make sure to use the lesser of the alignment of the source and the dest |
| // since we're changing where we're reading from, but don't want to increase |
| // the alignment past what can be read from or written to. |
| // TODO: Is this worth it if we're creating a less aligned memcpy? For |
| // example we could be moving from movaps -> movq on x86. |
| unsigned Align = std::min(MDep->getAlignment(), M->getAlignment()); |
| |
| IRBuilder<> Builder(M); |
| if (UseMemMove) |
| Builder.CreateMemMove(M->getRawDest(), MDep->getRawSource(), M->getLength(), |
| Align, M->isVolatile()); |
| else |
| Builder.CreateMemCpy(M->getRawDest(), MDep->getRawSource(), M->getLength(), |
| Align, M->isVolatile()); |
| |
| // Remove the instruction we're replacing. |
| MD->removeInstruction(M); |
| M->eraseFromParent(); |
| ++NumMemCpyInstr; |
| return true; |
| } |
| |
| |
| /// processMemCpy - 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 MemCpyOpt::processMemCpy(MemCpyInst *M) { |
| // We can only optimize statically-sized memcpy's that are non-volatile. |
| ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength()); |
| if (CopySize == 0 || 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())) { |
| IRBuilder<> Builder(M); |
| Builder.CreateMemSet(M->getRawDest(), ByteVal, CopySize, |
| M->getAlignment(), false); |
| MD->removeInstruction(M); |
| M->eraseFromParent(); |
| ++NumCpyToSet; |
| return true; |
| } |
| |
| // The are two possible optimizations we can do for memcpy: |
| // a) memcpy-memcpy xform which exposes redundance for DSE. |
| // b) call-memcpy xform for return slot optimization. |
| MemDepResult DepInfo = MD->getDependency(M); |
| if (!DepInfo.isClobber()) |
| return false; |
| |
| if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst())) |
| return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue()); |
| |
| if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) { |
| if (performCallSlotOptzn(M, M->getDest(), M->getSource(), |
| CopySize->getZExtValue(), C)) { |
| MD->removeInstruction(M); |
| M->eraseFromParent(); |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| /// processMemMove - Transforms memmove calls to memcpy calls when the src/dst |
| /// are guaranteed not to alias. |
| bool MemCpyOpt::processMemMove(MemMoveInst *M) { |
| AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); |
| |
| if (!TLI->has(LibFunc::memmove)) |
| return false; |
| |
| // See if the pointers alias. |
| if (!AA.isNoAlias(AA.getLocationForDest(M), AA.getLocationForSource(M))) |
| return false; |
| |
| DEBUG(dbgs() << "MemCpyOpt: Optimizing memmove -> memcpy: " << *M << "\n"); |
| |
| // If not, then we know we can transform this. |
| Module *Mod = M->getParent()->getParent()->getParent(); |
| const Type *ArgTys[3] = { M->getRawDest()->getType(), |
| M->getRawSource()->getType(), |
| M->getLength()->getType() }; |
| M->setCalledFunction(Intrinsic::getDeclaration(Mod, Intrinsic::memcpy, |
| ArgTys, 3)); |
| |
| // MemDep may have over conservative information about this instruction, just |
| // conservatively flush it from the cache. |
| MD->removeInstruction(M); |
| |
| ++NumMoveToCpy; |
| return true; |
| } |
| |
| /// processByValArgument - This is called on every byval argument in call sites. |
| bool MemCpyOpt::processByValArgument(CallSite CS, unsigned ArgNo) { |
| if (TD == 0) return false; |
| |
| // Find out what feeds this byval argument. |
| Value *ByValArg = CS.getArgument(ArgNo); |
| const Type *ByValTy =cast<PointerType>(ByValArg->getType())->getElementType(); |
| uint64_t ByValSize = TD->getTypeAllocSize(ByValTy); |
| MemDepResult DepInfo = |
| MD->getPointerDependencyFrom(AliasAnalysis::Location(ByValArg, ByValSize), |
| true, CS.getInstruction(), |
| 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 == 0 || 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 == 0 || 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+1); |
| 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. |
| if (MDep->getAlignment() < ByValAlign && |
| getOrEnforceKnownAlignment(MDep->getSource(),ByValAlign, TD) < ByValAlign) |
| 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(AliasAnalysis::getLocationForSource(MDep), |
| false, CS.getInstruction(), 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()); |
| |
| DEBUG(dbgs() << "MemCpyOpt: 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; |
| } |
| |
| /// iterateOnFunction - Executes one iteration of MemCpyOpt. |
| bool MemCpyOpt::iterateOnFunction(Function &F) { |
| bool MadeChange = false; |
| |
| // Walk all instruction in the function. |
| for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) { |
| 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 (CallSite CS = (Value*)I) { |
| for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) |
| if (CS.paramHasAttr(i+1, Attribute::ByVal)) |
| MadeChange |= processByValArgument(CS, i); |
| } |
| |
| // Reprocess the instruction if desired. |
| if (RepeatInstruction) { |
| if (BI != BB->begin()) --BI; |
| MadeChange = true; |
| } |
| } |
| } |
| |
| return MadeChange; |
| } |
| |
| // MemCpyOpt::runOnFunction - This is the main transformation entry point for a |
| // function. |
| // |
| bool MemCpyOpt::runOnFunction(Function &F) { |
| bool MadeChange = false; |
| MD = &getAnalysis<MemoryDependenceAnalysis>(); |
| TD = getAnalysisIfAvailable<TargetData>(); |
| TLI = &getAnalysis<TargetLibraryInfo>(); |
| |
| // 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 (1) { |
| if (!iterateOnFunction(F)) |
| break; |
| MadeChange = true; |
| } |
| |
| MD = 0; |
| return MadeChange; |
| } |