| //===- 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/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/Support/Debug.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Target/TargetData.h" |
| #include <list> |
| using namespace llvm; |
| |
| STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted"); |
| STATISTIC(NumMemSetInfer, "Number of memsets inferred"); |
| |
| /// isBytewiseValue - If the specified value can be set by repeating the same |
| /// byte in memory, return the i8 value that it is represented with. This is |
| /// true for all i8 values obviously, but is also true for i32 0, i32 -1, |
| /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated |
| /// byte store (e.g. i16 0x1234), return null. |
| static Value *isBytewiseValue(Value *V) { |
| // All byte-wide stores are splatable, even of arbitrary variables. |
| if (V->getType() == Type::Int8Ty) return V; |
| |
| // Constant float and double values can be handled as integer values if the |
| // corresponding integer value is "byteable". An important case is 0.0. |
| if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) { |
| if (CFP->getType() == Type::FloatTy) |
| V = ConstantExpr::getBitCast(CFP, Type::Int32Ty); |
| if (CFP->getType() == Type::DoubleTy) |
| V = ConstantExpr::getBitCast(CFP, Type::Int64Ty); |
| // Don't handle long double formats, which have strange constraints. |
| } |
| |
| // We can handle constant integers that are power of two in size and a |
| // multiple of 8 bits. |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { |
| unsigned Width = CI->getBitWidth(); |
| if (isPowerOf2_32(Width) && Width > 8) { |
| // We can handle this value if the recursive binary decomposition is the |
| // same at all levels. |
| APInt Val = CI->getValue(); |
| APInt Val2; |
| while (Val.getBitWidth() != 8) { |
| unsigned NextWidth = Val.getBitWidth()/2; |
| Val2 = Val.lshr(NextWidth); |
| Val2.trunc(Val.getBitWidth()/2); |
| Val.trunc(Val.getBitWidth()/2); |
| |
| // If the top/bottom halves aren't the same, reject it. |
| if (Val != Val2) |
| return 0; |
| } |
| return ConstantInt::get(Val); |
| } |
| } |
| |
| // Conceptually, we could handle things like: |
| // %a = zext i8 %X to i16 |
| // %b = shl i16 %a, 8 |
| // %c = or i16 %a, %b |
| // but until there is an example that actually needs this, it doesn't seem |
| // worth worrying about. |
| return 0; |
| } |
| |
| static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx, |
| bool &VariableIdxFound, 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, |
| TargetData &TD) { |
| // 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. |
| GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1); |
| GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2); |
| 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; |
| |
| bool VariableIdxFound = false; |
| 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<StoreInst*, 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; |
| |
| // 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; |
| TargetData &TD; |
| public: |
| MemsetRanges(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 addStore(int64_t OffsetFromFirst, StoreInst *SI); |
| }; |
| |
| } // end anon namespace |
| |
| |
| /// addStore - 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::addStore(int64_t Start, StoreInst *SI) { |
| int64_t End = Start+TD.getTypeStoreSize(SI->getOperand(0)->getType()); |
| |
| // 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. |
| 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 = SI->getPointerOperand(); |
| R.Alignment = SI->getAlignment(); |
| R.TheStores.push_back(SI); |
| return; |
| } |
| |
| // This store overlaps with I, add it. |
| I->TheStores.push_back(SI); |
| |
| // 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 = SI->getPointerOperand(); |
| } |
| |
| // 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 VISIBILITY_HIDDEN MemCpyOpt : public FunctionPass { |
| bool runOnFunction(Function &F); |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| MemCpyOpt() : FunctionPass(&ID) {} |
| |
| 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<TargetData>(); |
| AU.addPreserved<AliasAnalysis>(); |
| AU.addPreserved<MemoryDependenceAnalysis>(); |
| AU.addPreserved<TargetData>(); |
| } |
| |
| // Helper fuctions |
| bool processStore(StoreInst *SI, BasicBlock::iterator& BBI); |
| bool processMemCpy(MemCpyInst* M); |
| bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C); |
| bool iterateOnFunction(Function &F); |
| }; |
| |
| char MemCpyOpt::ID = 0; |
| } |
| |
| // createMemCpyOptPass - The public interface to this file... |
| FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); } |
| |
| static RegisterPass<MemCpyOpt> X("memcpyopt", |
| "MemCpy Optimization"); |
| |
| |
| |
| /// processStore - When GVN is 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 consequtive ones |
| /// (currently 4) it attempts to merge them together into a memcpy/memset. |
| bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator& BBI) { |
| if (SI->isVolatile()) return false; |
| |
| // 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. |
| Value *ByteVal = isBytewiseValue(SI->getOperand(0)); |
| if (!ByteVal) |
| return false; |
| |
| TargetData &TD = getAnalysis<TargetData>(); |
| AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); |
| |
| // 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); |
| |
| Value *StartPtr = SI->getPointerOperand(); |
| |
| BasicBlock::iterator BI = SI; |
| for (++BI; !isa<TerminatorInst>(BI); ++BI) { |
| if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) { |
| // If the call 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 (AA.getModRefBehavior(CallSite::get(BI)) == |
| AliasAnalysis::DoesNotAccessMemory) |
| continue; |
| |
| // TODO: If this is a memset, try to join it in. |
| |
| break; |
| } else if (isa<VAArgInst>(BI) || isa<LoadInst>(BI)) |
| break; |
| |
| // If this is a non-store instruction it is fine, ignore it. |
| StoreInst *NextStore = dyn_cast<StoreInst>(BI); |
| if (NextStore == 0) continue; |
| |
| // 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); |
| } |
| |
| // 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 false; |
| |
| // 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.addStore(0, SI); |
| |
| |
| Function *MemSetF = 0; |
| |
| // Now that we have full information about ranges, loop over the ranges and |
| // emit memset's for anything big enough to be worthwhile. |
| bool MadeChange = false; |
| 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. We put |
| // the memset right before the first instruction that isn't part of this |
| // memset block. This ensure that the memset is dominated by any addressing |
| // instruction needed by the start of the block. |
| BasicBlock::iterator InsertPt = BI; |
| |
| if (MemSetF == 0) { |
| const Type *Tys[] = {Type::Int64Ty}; |
| MemSetF = Intrinsic::getDeclaration(SI->getParent()->getParent() |
| ->getParent(), Intrinsic::memset, |
| Tys, 1); |
| } |
| |
| // Get the starting pointer of the block. |
| StartPtr = Range.StartPtr; |
| |
| // Cast the start ptr to be i8* as memset requires. |
| const Type *i8Ptr = PointerType::getUnqual(Type::Int8Ty); |
| if (StartPtr->getType() != i8Ptr) |
| StartPtr = new BitCastInst(StartPtr, i8Ptr, StartPtr->getNameStart(), |
| InsertPt); |
| |
| Value *Ops[] = { |
| StartPtr, ByteVal, // Start, value |
| ConstantInt::get(Type::Int64Ty, Range.End-Range.Start), // size |
| ConstantInt::get(Type::Int32Ty, Range.Alignment) // align |
| }; |
| Value *C = CallInst::Create(MemSetF, Ops, Ops+4, "", InsertPt); |
| DEBUG(cerr << "Replace stores:\n"; |
| for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i) |
| cerr << *Range.TheStores[i]; |
| cerr << "With: " << *C); C=C; |
| |
| // Don't invalidate the iterator |
| BBI = BI; |
| |
| // Zap all the stores. |
| for (SmallVector<StoreInst*, 16>::const_iterator SI = Range.TheStores.begin(), |
| SE = Range.TheStores.end(); SI != SE; ++SI) |
| (*SI)->eraseFromParent(); |
| ++NumMemSetInfer; |
| MadeChange = true; |
| } |
| |
| return MadeChange; |
| } |
| |
| |
| /// 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(MemCpyInst *cpy, 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. |
| Value* cpyDest = cpy->getDest(); |
| Value* cpySrc = cpy->getSource(); |
| CallSite CS = CallSite::get(C); |
| |
| // We need to be able to reason about the size of the memcpy, so we require |
| // that it be a constant. |
| ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength()); |
| if (!cpyLength) |
| return false; |
| |
| // 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. |
| TargetData& TD = getAnalysis<TargetData>(); |
| |
| ConstantInt* srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); |
| if (!srcArraySize) |
| return false; |
| |
| uint64_t srcSize = TD.getTypeAllocSize(srcAlloca->getAllocatedType()) * |
| srcArraySize->getZExtValue(); |
| |
| if (cpyLength->getZExtValue() < 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.back(); |
| srcUseList.pop_back(); |
| |
| 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, cpy->getRawDest(), 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, CastInst::CreatePointerCast(cpyDest, |
| CS.getArgument(i)->getType(), cpyDest->getName(), C)); |
| else |
| CS.setArgument(i, cpyDest); |
| } |
| |
| if (!changedArgument) |
| return false; |
| |
| // Drop any cached information about the call, because we may have changed |
| // its dependence information by changing its parameter. |
| MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); |
| MD.removeInstruction(C); |
| |
| // Remove the memcpy |
| MD.removeInstruction(cpy); |
| cpy->eraseFromParent(); |
| NumMemCpyInstr++; |
| |
| return true; |
| } |
| |
| /// processMemCpy - perform simplication 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) { |
| MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>(); |
| |
| // 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 dep = MD.getDependency(M); |
| if (!dep.isClobber()) |
| return false; |
| if (!isa<MemCpyInst>(dep.getInst())) { |
| if (CallInst* C = dyn_cast<CallInst>(dep.getInst())) |
| return performCallSlotOptzn(M, C); |
| return false; |
| } |
| |
| MemCpyInst* MDep = cast<MemCpyInst>(dep.getInst()); |
| |
| // We can only transforms memcpy's where the dest of one is the source of the |
| // other |
| if (M->getSource() != MDep->getDest()) |
| return false; |
| |
| // Second, the length of the memcpy's must be the same, or the preceeding one |
| // must be larger than the following one. |
| ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength()); |
| ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength()); |
| if (!C1 || !C2) |
| return false; |
| |
| uint64_t DepSize = C1->getValue().getZExtValue(); |
| uint64_t CpySize = C2->getValue().getZExtValue(); |
| |
| if (DepSize < CpySize) |
| return false; |
| |
| // Finally, we have to make sure that the dest of the second does not |
| // alias the source of the first |
| AliasAnalysis& AA = getAnalysis<AliasAnalysis>(); |
| if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) != |
| AliasAnalysis::NoAlias) |
| return false; |
| else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) != |
| AliasAnalysis::NoAlias) |
| return false; |
| else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize) |
| != AliasAnalysis::NoAlias) |
| return false; |
| |
| // If all checks passed, then we can transform these memcpy's |
| const Type *Tys[1]; |
| Tys[0] = M->getLength()->getType(); |
| Function* MemCpyFun = Intrinsic::getDeclaration( |
| M->getParent()->getParent()->getParent(), |
| M->getIntrinsicID(), Tys, 1); |
| |
| Value *Args[4] = { |
| M->getRawDest(), MDep->getRawSource(), M->getLength(), M->getAlignmentCst() |
| }; |
| |
| CallInst* C = CallInst::Create(MemCpyFun, Args, Args+4, "", M); |
| |
| |
| // If C and M don't interfere, then this is a valid transformation. If they |
| // did, this would mean that the two sources overlap, which would be bad. |
| if (MD.getDependency(C) == dep) { |
| MD.removeInstruction(M); |
| M->eraseFromParent(); |
| NumMemCpyInstr++; |
| return true; |
| } |
| |
| // Otherwise, there was no point in doing this, so we remove the call we |
| // inserted and act like nothing happened. |
| MD.removeInstruction(C); |
| C->eraseFromParent(); |
| return false; |
| } |
| |
| // MemCpyOpt::runOnFunction - This is the main transformation entry point for a |
| // function. |
| // |
| bool MemCpyOpt::runOnFunction(Function& F) { |
| |
| bool changed = false; |
| bool shouldContinue = true; |
| |
| while (shouldContinue) { |
| shouldContinue = iterateOnFunction(F); |
| changed |= shouldContinue; |
| } |
| |
| return changed; |
| } |
| |
| |
| // MemCpyOpt::iterateOnFunction - Executes one iteration of GVN |
| bool MemCpyOpt::iterateOnFunction(Function &F) { |
| bool changed_function = 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++; |
| |
| if (StoreInst *SI = dyn_cast<StoreInst>(I)) |
| changed_function |= processStore(SI, BI); |
| else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) { |
| changed_function |= processMemCpy(M); |
| } |
| } |
| } |
| |
| return changed_function; |
| } |