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If there are no legal integers, assume 1 byte. This makes more sense than using the pointer size as a guess for the maximum GPR width. It is conceivable to want to use some 64-bit pointers on a target where 64-bit integers aren't legal. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190817 91177308-0d34-0410-b5e6-96231b3b80d8
1030 lines
38 KiB
C++
1030 lines
38 KiB
C++
//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass performs various transformations related to eliminating memcpy
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// calls, or transforming sets of stores into memset's.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "memcpyopt"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/MemoryDependenceAnalysis.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetLibraryInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <list>
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using namespace llvm;
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STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
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STATISTIC(NumMemSetInfer, "Number of memsets inferred");
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STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy");
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STATISTIC(NumCpyToSet, "Number of memcpys converted to memset");
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static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
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bool &VariableIdxFound, const DataLayout &TD){
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// Skip over the first indices.
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gep_type_iterator GTI = gep_type_begin(GEP);
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for (unsigned i = 1; i != Idx; ++i, ++GTI)
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/*skip along*/;
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// Compute the offset implied by the rest of the indices.
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int64_t Offset = 0;
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for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
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ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
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if (OpC == 0)
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return VariableIdxFound = true;
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if (OpC->isZero()) continue; // No offset.
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// Handle struct indices, which add their field offset to the pointer.
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if (StructType *STy = dyn_cast<StructType>(*GTI)) {
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Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
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continue;
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}
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// Otherwise, we have a sequential type like an array or vector. Multiply
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// the index by the ElementSize.
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uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
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Offset += Size*OpC->getSExtValue();
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}
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return Offset;
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}
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/// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a
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/// constant offset, and return that constant offset. For example, Ptr1 might
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/// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8.
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static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
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const DataLayout &TD) {
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Ptr1 = Ptr1->stripPointerCasts();
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Ptr2 = Ptr2->stripPointerCasts();
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GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
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GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
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bool VariableIdxFound = false;
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// If one pointer is a GEP and the other isn't, then see if the GEP is a
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// constant offset from the base, as in "P" and "gep P, 1".
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if (GEP1 && GEP2 == 0 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
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Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, TD);
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return !VariableIdxFound;
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}
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if (GEP2 && GEP1 == 0 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
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Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, TD);
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return !VariableIdxFound;
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}
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// Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
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// base. After that base, they may have some number of common (and
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// potentially variable) indices. After that they handle some constant
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// offset, which determines their offset from each other. At this point, we
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// handle no other case.
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if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
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return false;
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// Skip any common indices and track the GEP types.
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unsigned Idx = 1;
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for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
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if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
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break;
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int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD);
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int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD);
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if (VariableIdxFound) return false;
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Offset = Offset2-Offset1;
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return true;
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}
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/// MemsetRange - Represents a range of memset'd bytes with the ByteVal value.
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/// This allows us to analyze stores like:
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/// store 0 -> P+1
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/// store 0 -> P+0
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/// store 0 -> P+3
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/// store 0 -> P+2
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/// which sometimes happens with stores to arrays of structs etc. When we see
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/// the first store, we make a range [1, 2). The second store extends the range
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/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
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/// two ranges into [0, 3) which is memset'able.
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namespace {
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struct MemsetRange {
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// Start/End - A semi range that describes the span that this range covers.
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// The range is closed at the start and open at the end: [Start, End).
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int64_t Start, End;
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/// StartPtr - The getelementptr instruction that points to the start of the
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/// range.
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Value *StartPtr;
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/// Alignment - The known alignment of the first store.
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unsigned Alignment;
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/// TheStores - The actual stores that make up this range.
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SmallVector<Instruction*, 16> TheStores;
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bool isProfitableToUseMemset(const DataLayout &TD) const;
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};
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} // end anon namespace
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bool MemsetRange::isProfitableToUseMemset(const DataLayout &TD) const {
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// If we found more than 4 stores to merge or 16 bytes, use memset.
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if (TheStores.size() >= 4 || End-Start >= 16) return true;
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// If there is nothing to merge, don't do anything.
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if (TheStores.size() < 2) return false;
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// If any of the stores are a memset, then it is always good to extend the
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// memset.
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for (unsigned i = 0, e = TheStores.size(); i != e; ++i)
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if (!isa<StoreInst>(TheStores[i]))
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return true;
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// Assume that the code generator is capable of merging pairs of stores
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// together if it wants to.
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if (TheStores.size() == 2) return false;
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// If we have fewer than 8 stores, it can still be worthwhile to do this.
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// For example, merging 4 i8 stores into an i32 store is useful almost always.
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// However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
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// memset will be split into 2 32-bit stores anyway) and doing so can
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// pessimize the llvm optimizer.
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//
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// Since we don't have perfect knowledge here, make some assumptions: assume
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// the maximum GPR width is the same size as the largest legal integer
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// size. If so, check to see whether we will end up actually reducing the
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// number of stores used.
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unsigned Bytes = unsigned(End-Start);
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unsigned MaxIntSize = TD.getLargestLegalIntTypeSize();
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if (MaxIntSize == 0)
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MaxIntSize = 1;
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unsigned NumPointerStores = Bytes / MaxIntSize;
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// Assume the remaining bytes if any are done a byte at a time.
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unsigned NumByteStores = Bytes - NumPointerStores * MaxIntSize;
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// If we will reduce the # stores (according to this heuristic), do the
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// transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
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// etc.
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return TheStores.size() > NumPointerStores+NumByteStores;
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}
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namespace {
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class MemsetRanges {
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/// Ranges - A sorted list of the memset ranges. We use std::list here
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/// because each element is relatively large and expensive to copy.
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std::list<MemsetRange> Ranges;
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typedef std::list<MemsetRange>::iterator range_iterator;
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const DataLayout &TD;
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public:
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MemsetRanges(const DataLayout &td) : TD(td) {}
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typedef std::list<MemsetRange>::const_iterator const_iterator;
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const_iterator begin() const { return Ranges.begin(); }
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const_iterator end() const { return Ranges.end(); }
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bool empty() const { return Ranges.empty(); }
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void addInst(int64_t OffsetFromFirst, Instruction *Inst) {
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if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
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addStore(OffsetFromFirst, SI);
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else
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addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst));
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}
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void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
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int64_t StoreSize = TD.getTypeStoreSize(SI->getOperand(0)->getType());
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addRange(OffsetFromFirst, StoreSize,
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SI->getPointerOperand(), SI->getAlignment(), SI);
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}
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void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
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int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue();
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addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getAlignment(), MSI);
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}
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void addRange(int64_t Start, int64_t Size, Value *Ptr,
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unsigned Alignment, Instruction *Inst);
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};
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} // end anon namespace
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/// addRange - Add a new store to the MemsetRanges data structure. This adds a
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/// new range for the specified store at the specified offset, merging into
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/// existing ranges as appropriate.
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///
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/// Do a linear search of the ranges to see if this can be joined and/or to
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/// find the insertion point in the list. We keep the ranges sorted for
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/// simplicity here. This is a linear search of a linked list, which is ugly,
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/// however the number of ranges is limited, so this won't get crazy slow.
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void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr,
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unsigned Alignment, Instruction *Inst) {
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int64_t End = Start+Size;
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range_iterator I = Ranges.begin(), E = Ranges.end();
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while (I != E && Start > I->End)
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++I;
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// We now know that I == E, in which case we didn't find anything to merge
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// with, or that Start <= I->End. If End < I->Start or I == E, then we need
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// to insert a new range. Handle this now.
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if (I == E || End < I->Start) {
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MemsetRange &R = *Ranges.insert(I, MemsetRange());
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R.Start = Start;
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R.End = End;
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R.StartPtr = Ptr;
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R.Alignment = Alignment;
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R.TheStores.push_back(Inst);
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return;
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}
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// This store overlaps with I, add it.
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I->TheStores.push_back(Inst);
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// At this point, we may have an interval that completely contains our store.
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// If so, just add it to the interval and return.
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if (I->Start <= Start && I->End >= End)
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return;
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// Now we know that Start <= I->End and End >= I->Start so the range overlaps
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// but is not entirely contained within the range.
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// See if the range extends the start of the range. In this case, it couldn't
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// possibly cause it to join the prior range, because otherwise we would have
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// stopped on *it*.
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if (Start < I->Start) {
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I->Start = Start;
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I->StartPtr = Ptr;
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I->Alignment = Alignment;
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}
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// Now we know that Start <= I->End and Start >= I->Start (so the startpoint
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// is in or right at the end of I), and that End >= I->Start. Extend I out to
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// End.
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if (End > I->End) {
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I->End = End;
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range_iterator NextI = I;
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while (++NextI != E && End >= NextI->Start) {
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// Merge the range in.
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I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
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if (NextI->End > I->End)
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I->End = NextI->End;
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Ranges.erase(NextI);
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NextI = I;
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}
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}
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}
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//===----------------------------------------------------------------------===//
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// MemCpyOpt Pass
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//===----------------------------------------------------------------------===//
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namespace {
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class MemCpyOpt : public FunctionPass {
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MemoryDependenceAnalysis *MD;
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TargetLibraryInfo *TLI;
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const DataLayout *TD;
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public:
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static char ID; // Pass identification, replacement for typeid
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MemCpyOpt() : FunctionPass(ID) {
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initializeMemCpyOptPass(*PassRegistry::getPassRegistry());
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MD = 0;
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TLI = 0;
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TD = 0;
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}
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bool runOnFunction(Function &F);
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private:
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// This transformation requires dominator postdominator info
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<DominatorTree>();
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AU.addRequired<MemoryDependenceAnalysis>();
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AU.addRequired<AliasAnalysis>();
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AU.addRequired<TargetLibraryInfo>();
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AU.addPreserved<AliasAnalysis>();
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AU.addPreserved<MemoryDependenceAnalysis>();
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}
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// Helper fuctions
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bool processStore(StoreInst *SI, BasicBlock::iterator &BBI);
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bool processMemSet(MemSetInst *SI, BasicBlock::iterator &BBI);
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bool processMemCpy(MemCpyInst *M);
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bool processMemMove(MemMoveInst *M);
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bool performCallSlotOptzn(Instruction *cpy, Value *cpyDst, Value *cpySrc,
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uint64_t cpyLen, unsigned cpyAlign, CallInst *C);
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bool processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
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uint64_t MSize);
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bool processByValArgument(CallSite CS, unsigned ArgNo);
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Instruction *tryMergingIntoMemset(Instruction *I, Value *StartPtr,
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Value *ByteVal);
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bool iterateOnFunction(Function &F);
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};
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char MemCpyOpt::ID = 0;
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}
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// createMemCpyOptPass - The public interface to this file...
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FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); }
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INITIALIZE_PASS_BEGIN(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
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false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTree)
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INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
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INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
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INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
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false, false)
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/// tryMergingIntoMemset - When scanning forward over instructions, we look for
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/// some other patterns to fold away. In particular, this looks for stores to
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/// neighboring locations of memory. If it sees enough consecutive ones, it
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/// attempts to merge them together into a memcpy/memset.
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Instruction *MemCpyOpt::tryMergingIntoMemset(Instruction *StartInst,
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Value *StartPtr, Value *ByteVal) {
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if (TD == 0) return 0;
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// Okay, so we now have a single store that can be splatable. Scan to find
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// all subsequent stores of the same value to offset from the same pointer.
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// Join these together into ranges, so we can decide whether contiguous blocks
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// are stored.
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MemsetRanges Ranges(*TD);
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BasicBlock::iterator BI = StartInst;
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for (++BI; !isa<TerminatorInst>(BI); ++BI) {
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if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) {
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// If the instruction is readnone, ignore it, otherwise bail out. We
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// don't even allow readonly here because we don't want something like:
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// A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
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if (BI->mayWriteToMemory() || BI->mayReadFromMemory())
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break;
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continue;
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}
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if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
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// If this is a store, see if we can merge it in.
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if (!NextStore->isSimple()) break;
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// Check to see if this stored value is of the same byte-splattable value.
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if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
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break;
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// Check to see if this store is to a constant offset from the start ptr.
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int64_t Offset;
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if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(),
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Offset, *TD))
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break;
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Ranges.addStore(Offset, NextStore);
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} else {
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MemSetInst *MSI = cast<MemSetInst>(BI);
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if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
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!isa<ConstantInt>(MSI->getLength()))
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break;
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// Check to see if this store is to a constant offset from the start ptr.
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int64_t Offset;
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if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, *TD))
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break;
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Ranges.addMemSet(Offset, MSI);
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}
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}
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// If we have no ranges, then we just had a single store with nothing that
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// could be merged in. This is a very common case of course.
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if (Ranges.empty())
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return 0;
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// If we had at least one store that could be merged in, add the starting
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// store as well. We try to avoid this unless there is at least something
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// interesting as a small compile-time optimization.
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Ranges.addInst(0, StartInst);
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// If we create any memsets, we put it right before the first instruction that
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// isn't part of the memset block. This ensure that the memset is dominated
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// by any addressing instruction needed by the start of the block.
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IRBuilder<> Builder(BI);
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// Now that we have full information about ranges, loop over the ranges and
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// emit memset's for anything big enough to be worthwhile.
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Instruction *AMemSet = 0;
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for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
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I != E; ++I) {
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const MemsetRange &Range = *I;
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if (Range.TheStores.size() == 1) continue;
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// If it is profitable to lower this range to memset, do so now.
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if (!Range.isProfitableToUseMemset(*TD))
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continue;
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// Otherwise, we do want to transform this! Create a new memset.
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// Get the starting pointer of the block.
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StartPtr = Range.StartPtr;
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// Determine alignment
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unsigned Alignment = Range.Alignment;
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if (Alignment == 0) {
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Type *EltType =
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cast<PointerType>(StartPtr->getType())->getElementType();
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Alignment = TD->getABITypeAlignment(EltType);
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|
}
|
|
|
|
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 (SmallVectorImpl<Instruction *>::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->isSimple()) 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->isSimple() && 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) {
|
|
unsigned storeAlign = SI->getAlignment();
|
|
if (!storeAlign)
|
|
storeAlign = TD->getABITypeAlignment(SI->getOperand(0)->getType());
|
|
unsigned loadAlign = LI->getAlignment();
|
|
if (!loadAlign)
|
|
loadAlign = TD->getABITypeAlignment(LI->getType());
|
|
|
|
bool changed = performCallSlotOptzn(LI,
|
|
SI->getPointerOperand()->stripPointerCasts(),
|
|
LI->getPointerOperand()->stripPointerCasts(),
|
|
TD->getTypeStoreSize(SI->getOperand(0)->getType()),
|
|
std::min(storeAlign, loadAlign), 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, 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.
|
|
|
|
// 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;
|
|
|
|
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 = TD->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 = TD->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->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>();
|
|
AliasAnalysis::ModRefResult MR = AA.getModRefInfo(C, cpyDest, srcSize);
|
|
// If necessary, perform additional analysis.
|
|
if (MR != AliasAnalysis::NoModRef)
|
|
MR = AA.callCapturesBefore(C, cpyDest, srcSize, &DT);
|
|
if (MR != 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) {
|
|
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(srcAlign);
|
|
}
|
|
|
|
// 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()) {
|
|
if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
|
|
if (performCallSlotOptzn(M, M->getDest(), M->getSource(),
|
|
CopySize->getZExtValue(), M->getAlignment(),
|
|
C)) {
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
AliasAnalysis::Location SrcLoc = AliasAnalysis::getLocationForSource(M);
|
|
MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(SrcLoc, true,
|
|
M, M->getParent());
|
|
if (SrcDepInfo.isClobber()) {
|
|
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
|
|
return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue());
|
|
}
|
|
|
|
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();
|
|
Type *ArgTys[3] = { M->getRawDest()->getType(),
|
|
M->getRawSource()->getType(),
|
|
M->getLength()->getType() };
|
|
M->setCalledFunction(Intrinsic::getDeclaration(Mod, 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;
|
|
}
|
|
|
|
/// 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);
|
|
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.isByValArgument(i))
|
|
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<DataLayout>();
|
|
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;
|
|
}
|