forked from OSchip/llvm-project
1446 lines
53 KiB
C++
1446 lines
53 KiB
C++
//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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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#include "llvm/Transforms/Scalar/MemCpyOptimizer.h"
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/None.h"
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#include "llvm/ADT/STLExtras.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/ADT/iterator_range.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/MemoryDependenceAnalysis.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GetElementPtrTypeIterator.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/InstrTypes.h"
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#include "llvm/IR/Instruction.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/IR/Intrinsics.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/Value.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <algorithm>
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#include <cassert>
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#include <cstdint>
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#include <utility>
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using namespace llvm;
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#define DEBUG_TYPE "memcpyopt"
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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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namespace {
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/// 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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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 &DL) const;
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};
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} // end anonymous namespace
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bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) 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 (Instruction *SI : TheStores)
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if (!isa<StoreInst>(SI))
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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 = DL.getLargestLegalIntTypeSizeInBits() / 8;
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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 % 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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using range_iterator = SmallVectorImpl<MemsetRange>::iterator;
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/// A sorted list of the memset ranges.
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SmallVector<MemsetRange, 8> Ranges;
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const DataLayout &DL;
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public:
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MemsetRanges(const DataLayout &DL) : DL(DL) {}
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using const_iterator = SmallVectorImpl<MemsetRange>::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 = DL.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->getDestAlignment(), 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 anonymous namespace
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/// 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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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 = partition_point(
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Ranges, [=](const MemsetRange &O) { return O.End < Start; });
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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 == Ranges.end() || 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 != Ranges.end() && 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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// MemCpyOptLegacyPass Pass
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//===----------------------------------------------------------------------===//
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namespace {
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class MemCpyOptLegacyPass : public FunctionPass {
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MemCpyOptPass Impl;
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public:
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static char ID; // Pass identification, replacement for typeid
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MemCpyOptLegacyPass() : FunctionPass(ID) {
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initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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private:
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// This transformation requires dominator postdominator info
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<AssumptionCacheTracker>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<MemoryDependenceWrapperPass>();
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AU.addRequired<AAResultsWrapperPass>();
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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AU.addPreserved<GlobalsAAWrapperPass>();
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AU.addPreserved<MemoryDependenceWrapperPass>();
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}
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};
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} // end anonymous namespace
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char MemCpyOptLegacyPass::ID = 0;
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/// The public interface to this file...
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FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); }
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INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
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false, false)
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INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
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INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
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false, false)
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/// When scanning forward over instructions, we look for some other patterns to
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/// fold away. In particular, this looks for stores to neighboring locations of
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/// memory. If it sees enough consecutive ones, it attempts to merge them
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/// together into a memcpy/memset.
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Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,
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Value *StartPtr,
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Value *ByteVal) {
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const DataLayout &DL = StartInst->getModule()->getDataLayout();
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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(DL);
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BasicBlock::iterator BI(StartInst);
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for (++BI; !BI->isTerminator(); ++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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Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL);
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if (isa<UndefValue>(ByteVal) && StoredByte)
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ByteVal = StoredByte;
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if (ByteVal != StoredByte)
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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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Optional<int64_t> Offset =
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isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL);
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if (!Offset)
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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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Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL);
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if (!Offset)
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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 nullptr;
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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 = nullptr;
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for (const MemsetRange &Range : Ranges) {
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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(DL))
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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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const Align Alignment = DL.getValueOrABITypeAlignment(
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MaybeAlign(Range.Alignment),
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cast<PointerType>(StartPtr->getType())->getElementType());
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AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End - Range.Start,
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Alignment);
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LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI
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: Range.TheStores) dbgs()
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<< *SI << '\n';
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dbgs() << "With: " << *AMemSet << '\n');
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if (!Range.TheStores.empty())
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AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
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// Zap all the stores.
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for (Instruction *SI : Range.TheStores) {
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MD->removeInstruction(SI);
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SI->eraseFromParent();
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}
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++NumMemSetInfer;
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}
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return AMemSet;
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}
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static Align findStoreAlignment(const DataLayout &DL, const StoreInst *SI) {
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return DL.getValueOrABITypeAlignment(MaybeAlign(SI->getAlignment()),
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SI->getOperand(0)->getType());
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}
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static Align findLoadAlignment(const DataLayout &DL, const LoadInst *LI) {
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return DL.getValueOrABITypeAlignment(MaybeAlign(LI->getAlignment()),
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LI->getType());
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}
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static Align findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
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const LoadInst *LI) {
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Align StoreAlign = findStoreAlignment(DL, SI);
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Align LoadAlign = findLoadAlignment(DL, LI);
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return commonAlignment(StoreAlign, LoadAlign);
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}
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// This method try to lift a store instruction before position P.
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// It will lift the store and its argument + that anything that
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// may alias with these.
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// The method returns true if it was successful.
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static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P,
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const LoadInst *LI) {
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// If the store alias this position, early bail out.
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MemoryLocation StoreLoc = MemoryLocation::get(SI);
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if (isModOrRefSet(AA.getModRefInfo(P, StoreLoc)))
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return false;
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// Keep track of the arguments of all instruction we plan to lift
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// so we can make sure to lift them as well if appropriate.
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DenseSet<Instruction*> Args;
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if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand()))
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if (Ptr->getParent() == SI->getParent())
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Args.insert(Ptr);
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// Instruction to lift before P.
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SmallVector<Instruction*, 8> ToLift;
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// Memory locations of lifted instructions.
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SmallVector<MemoryLocation, 8> MemLocs{StoreLoc};
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// Lifted calls.
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SmallVector<const CallBase *, 8> Calls;
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const MemoryLocation LoadLoc = MemoryLocation::get(LI);
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for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
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auto *C = &*I;
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bool MayAlias = isModOrRefSet(AA.getModRefInfo(C, None));
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bool NeedLift = false;
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if (Args.erase(C))
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NeedLift = true;
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else if (MayAlias) {
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NeedLift = llvm::any_of(MemLocs, [C, &AA](const MemoryLocation &ML) {
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return isModOrRefSet(AA.getModRefInfo(C, ML));
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});
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if (!NeedLift)
|
|
NeedLift = llvm::any_of(Calls, [C, &AA](const CallBase *Call) {
|
|
return isModOrRefSet(AA.getModRefInfo(C, Call));
|
|
});
|
|
}
|
|
|
|
if (!NeedLift)
|
|
continue;
|
|
|
|
if (MayAlias) {
|
|
// Since LI is implicitly moved downwards past the lifted instructions,
|
|
// none of them may modify its source.
|
|
if (isModSet(AA.getModRefInfo(C, LoadLoc)))
|
|
return false;
|
|
else if (const auto *Call = dyn_cast<CallBase>(C)) {
|
|
// If we can't lift this before P, it's game over.
|
|
if (isModOrRefSet(AA.getModRefInfo(P, Call)))
|
|
return false;
|
|
|
|
Calls.push_back(Call);
|
|
} else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) {
|
|
// If we can't lift this before P, it's game over.
|
|
auto ML = MemoryLocation::get(C);
|
|
if (isModOrRefSet(AA.getModRefInfo(P, ML)))
|
|
return false;
|
|
|
|
MemLocs.push_back(ML);
|
|
} else
|
|
// We don't know how to lift this instruction.
|
|
return false;
|
|
}
|
|
|
|
ToLift.push_back(C);
|
|
for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
|
|
if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) {
|
|
if (A->getParent() == SI->getParent()) {
|
|
// Cannot hoist user of P above P
|
|
if(A == P) return false;
|
|
Args.insert(A);
|
|
}
|
|
}
|
|
}
|
|
|
|
// We made it, we need to lift
|
|
for (auto *I : llvm::reverse(ToLift)) {
|
|
LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n");
|
|
I->moveBefore(P);
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
|
|
if (!SI->isSimple()) return false;
|
|
|
|
// Avoid merging nontemporal stores since the resulting
|
|
// memcpy/memset would not be able to preserve the nontemporal hint.
|
|
// In theory we could teach how to propagate the !nontemporal metadata to
|
|
// memset calls. However, that change would force the backend to
|
|
// conservatively expand !nontemporal memset calls back to sequences of
|
|
// store instructions (effectively undoing the merging).
|
|
if (SI->getMetadata(LLVMContext::MD_nontemporal))
|
|
return false;
|
|
|
|
const DataLayout &DL = SI->getModule()->getDataLayout();
|
|
|
|
// Load to store forwarding can be interpreted as memcpy.
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
|
|
if (LI->isSimple() && LI->hasOneUse() &&
|
|
LI->getParent() == SI->getParent()) {
|
|
|
|
auto *T = LI->getType();
|
|
if (T->isAggregateType()) {
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
MemoryLocation LoadLoc = MemoryLocation::get(LI);
|
|
|
|
// We use alias analysis to check if an instruction may store to
|
|
// the memory we load from in between the load and the store. If
|
|
// such an instruction is found, we try to promote there instead
|
|
// of at the store position.
|
|
Instruction *P = SI;
|
|
for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
|
|
if (isModSet(AA.getModRefInfo(&I, LoadLoc))) {
|
|
P = &I;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// We found an instruction that may write to the loaded memory.
|
|
// We can try to promote at this position instead of the store
|
|
// position if nothing alias the store memory after this and the store
|
|
// destination is not in the range.
|
|
if (P && P != SI) {
|
|
if (!moveUp(AA, SI, P, LI))
|
|
P = nullptr;
|
|
}
|
|
|
|
// If a valid insertion position is found, then we can promote
|
|
// the load/store pair to a memcpy.
|
|
if (P) {
|
|
// If we load from memory that may alias the memory we store to,
|
|
// memmove must be used to preserve semantic. If not, memcpy can
|
|
// be used.
|
|
bool UseMemMove = false;
|
|
if (!AA.isNoAlias(MemoryLocation::get(SI), LoadLoc))
|
|
UseMemMove = true;
|
|
|
|
uint64_t Size = DL.getTypeStoreSize(T);
|
|
|
|
IRBuilder<> Builder(P);
|
|
Instruction *M;
|
|
if (UseMemMove)
|
|
M = Builder.CreateMemMove(
|
|
SI->getPointerOperand(), findStoreAlignment(DL, SI),
|
|
LI->getPointerOperand(), findLoadAlignment(DL, LI), Size);
|
|
else
|
|
M = Builder.CreateMemCpy(
|
|
SI->getPointerOperand(), findStoreAlignment(DL, SI),
|
|
LI->getPointerOperand(), findLoadAlignment(DL, LI), Size);
|
|
|
|
LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => "
|
|
<< *M << "\n");
|
|
|
|
MD->removeInstruction(SI);
|
|
SI->eraseFromParent();
|
|
MD->removeInstruction(LI);
|
|
LI->eraseFromParent();
|
|
++NumMemCpyInstr;
|
|
|
|
// Make sure we do not invalidate the iterator.
|
|
BBI = M->getIterator();
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// Detect cases where we're performing call slot forwarding, but
|
|
// happen to be using a load-store pair to implement it, rather than
|
|
// a memcpy.
|
|
MemDepResult ldep = MD->getDependency(LI);
|
|
CallInst *C = nullptr;
|
|
if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
|
|
C = dyn_cast<CallInst>(ldep.getInst());
|
|
|
|
if (C) {
|
|
// Check that nothing touches the dest of the "copy" between
|
|
// the call and the store.
|
|
Value *CpyDest = SI->getPointerOperand()->stripPointerCasts();
|
|
bool CpyDestIsLocal = isa<AllocaInst>(CpyDest);
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
MemoryLocation StoreLoc = MemoryLocation::get(SI);
|
|
for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator();
|
|
I != E; --I) {
|
|
if (isModOrRefSet(AA.getModRefInfo(&*I, StoreLoc))) {
|
|
C = nullptr;
|
|
break;
|
|
}
|
|
// The store to dest may never happen if an exception can be thrown
|
|
// between the load and the store.
|
|
if (I->mayThrow() && !CpyDestIsLocal) {
|
|
C = nullptr;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (C) {
|
|
bool changed = performCallSlotOptzn(
|
|
LI, SI->getPointerOperand()->stripPointerCasts(),
|
|
LI->getPointerOperand()->stripPointerCasts(),
|
|
DL.getTypeStoreSize(SI->getOperand(0)->getType()),
|
|
findCommonAlignment(DL, SI, LI).value(), C);
|
|
if (changed) {
|
|
MD->removeInstruction(SI);
|
|
SI->eraseFromParent();
|
|
MD->removeInstruction(LI);
|
|
LI->eraseFromParent();
|
|
++NumMemCpyInstr;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// There are two cases that are interesting for this code to handle: memcpy
|
|
// and memset. Right now we only handle memset.
|
|
|
|
// Ensure that the value being stored is something that can be memset'able a
|
|
// byte at a time like "0" or "-1" or any width, as well as things like
|
|
// 0xA0A0A0A0 and 0.0.
|
|
auto *V = SI->getOperand(0);
|
|
if (Value *ByteVal = isBytewiseValue(V, DL)) {
|
|
if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
|
|
ByteVal)) {
|
|
BBI = I->getIterator(); // Don't invalidate iterator.
|
|
return true;
|
|
}
|
|
|
|
// If we have an aggregate, we try to promote it to memset regardless
|
|
// of opportunity for merging as it can expose optimization opportunities
|
|
// in subsequent passes.
|
|
auto *T = V->getType();
|
|
if (T->isAggregateType()) {
|
|
uint64_t Size = DL.getTypeStoreSize(T);
|
|
const Align MA =
|
|
DL.getValueOrABITypeAlignment(MaybeAlign(SI->getAlignment()), T);
|
|
IRBuilder<> Builder(SI);
|
|
auto *M =
|
|
Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size, MA);
|
|
|
|
LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n");
|
|
|
|
MD->removeInstruction(SI);
|
|
SI->eraseFromParent();
|
|
NumMemSetInfer++;
|
|
|
|
// Make sure we do not invalidate the iterator.
|
|
BBI = M->getIterator();
|
|
return true;
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
|
|
// See if there is another memset or store neighboring this memset which
|
|
// allows us to widen out the memset to do a single larger store.
|
|
if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
|
|
if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
|
|
MSI->getValue())) {
|
|
BBI = I->getIterator(); // Don't invalidate iterator.
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// Takes a memcpy and a call that it depends on,
|
|
/// and checks for the possibility of a call slot optimization by having
|
|
/// the call write its result directly into the destination of the memcpy.
|
|
bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpy, Value *cpyDest,
|
|
Value *cpySrc, uint64_t cpyLen,
|
|
unsigned cpyAlign, CallInst *C) {
|
|
// The general transformation to keep in mind is
|
|
//
|
|
// call @func(..., src, ...)
|
|
// memcpy(dest, src, ...)
|
|
//
|
|
// ->
|
|
//
|
|
// memcpy(dest, src, ...)
|
|
// call @func(..., dest, ...)
|
|
//
|
|
// Since moving the memcpy is technically awkward, we additionally check that
|
|
// src only holds uninitialized values at the moment of the call, meaning that
|
|
// the memcpy can be discarded rather than moved.
|
|
|
|
// Lifetime marks shouldn't be operated on.
|
|
if (Function *F = C->getCalledFunction())
|
|
if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start)
|
|
return false;
|
|
|
|
// Deliberately get the source and destination with bitcasts stripped away,
|
|
// because we'll need to do type comparisons based on the underlying type.
|
|
CallSite CS(C);
|
|
|
|
// Require that src be an alloca. This simplifies the reasoning considerably.
|
|
AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
|
|
if (!srcAlloca)
|
|
return false;
|
|
|
|
ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
|
|
if (!srcArraySize)
|
|
return false;
|
|
|
|
const DataLayout &DL = cpy->getModule()->getDataLayout();
|
|
uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) *
|
|
srcArraySize->getZExtValue();
|
|
|
|
if (cpyLen < srcSize)
|
|
return false;
|
|
|
|
// Check that accessing the first srcSize bytes of dest will not cause a
|
|
// trap. Otherwise the transform is invalid since it might cause a trap
|
|
// to occur earlier than it otherwise would.
|
|
if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) {
|
|
// The destination is an alloca. Check it is larger than srcSize.
|
|
ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
|
|
if (!destArraySize)
|
|
return false;
|
|
|
|
uint64_t destSize = DL.getTypeAllocSize(A->getAllocatedType()) *
|
|
destArraySize->getZExtValue();
|
|
|
|
if (destSize < srcSize)
|
|
return false;
|
|
} else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
|
|
// The store to dest may never happen if the call can throw.
|
|
if (C->mayThrow())
|
|
return false;
|
|
|
|
if (A->getDereferenceableBytes() < srcSize) {
|
|
// If the destination is an sret parameter then only accesses that are
|
|
// outside of the returned struct type can trap.
|
|
if (!A->hasStructRetAttr())
|
|
return false;
|
|
|
|
Type *StructTy = cast<PointerType>(A->getType())->getElementType();
|
|
if (!StructTy->isSized()) {
|
|
// The call may never return and hence the copy-instruction may never
|
|
// be executed, and therefore it's not safe to say "the destination
|
|
// has at least <cpyLen> bytes, as implied by the copy-instruction",
|
|
return false;
|
|
}
|
|
|
|
uint64_t destSize = DL.getTypeAllocSize(StructTy);
|
|
if (destSize < srcSize)
|
|
return false;
|
|
}
|
|
} else {
|
|
return false;
|
|
}
|
|
|
|
// Check that dest points to memory that is at least as aligned as src.
|
|
unsigned srcAlign = srcAlloca->getAlignment();
|
|
if (!srcAlign)
|
|
srcAlign = DL.getABITypeAlignment(srcAlloca->getAllocatedType());
|
|
bool isDestSufficientlyAligned = srcAlign <= cpyAlign;
|
|
// If dest is not aligned enough and we can't increase its alignment then
|
|
// bail out.
|
|
if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest))
|
|
return false;
|
|
|
|
// Check that src is not accessed except via the call and the memcpy. This
|
|
// guarantees that it holds only undefined values when passed in (so the final
|
|
// memcpy can be dropped), that it is not read or written between the call and
|
|
// the memcpy, and that writing beyond the end of it is undefined.
|
|
SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(),
|
|
srcAlloca->user_end());
|
|
while (!srcUseList.empty()) {
|
|
User *U = srcUseList.pop_back_val();
|
|
|
|
if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
|
|
for (User *UU : U->users())
|
|
srcUseList.push_back(UU);
|
|
continue;
|
|
}
|
|
if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
|
|
if (!G->hasAllZeroIndices())
|
|
return false;
|
|
|
|
for (User *UU : U->users())
|
|
srcUseList.push_back(UU);
|
|
continue;
|
|
}
|
|
if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
|
|
if (IT->isLifetimeStartOrEnd())
|
|
continue;
|
|
|
|
if (U != C && U != cpy)
|
|
return false;
|
|
}
|
|
|
|
// Check that src isn't captured by the called function since the
|
|
// transformation can cause aliasing issues in that case.
|
|
for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
|
|
if (CS.getArgument(i) == cpySrc && !CS.doesNotCapture(i))
|
|
return false;
|
|
|
|
// Since we're changing the parameter to the callsite, we need to make sure
|
|
// that what would be the new parameter dominates the callsite.
|
|
DominatorTree &DT = LookupDomTree();
|
|
if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest))
|
|
if (!DT.dominates(cpyDestInst, C))
|
|
return false;
|
|
|
|
// In addition to knowing that the call does not access src in some
|
|
// unexpected manner, for example via a global, which we deduce from
|
|
// the use analysis, we also need to know that it does not sneakily
|
|
// access dest. We rely on AA to figure this out for us.
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
ModRefInfo MR = AA.getModRefInfo(C, cpyDest, LocationSize::precise(srcSize));
|
|
// If necessary, perform additional analysis.
|
|
if (isModOrRefSet(MR))
|
|
MR = AA.callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), &DT);
|
|
if (isModOrRefSet(MR))
|
|
return false;
|
|
|
|
// We can't create address space casts here because we don't know if they're
|
|
// safe for the target.
|
|
if (cpySrc->getType()->getPointerAddressSpace() !=
|
|
cpyDest->getType()->getPointerAddressSpace())
|
|
return false;
|
|
for (unsigned i = 0; i < CS.arg_size(); ++i)
|
|
if (CS.getArgument(i)->stripPointerCasts() == cpySrc &&
|
|
cpySrc->getType()->getPointerAddressSpace() !=
|
|
CS.getArgument(i)->getType()->getPointerAddressSpace())
|
|
return false;
|
|
|
|
// All the checks have passed, so do the transformation.
|
|
bool changedArgument = false;
|
|
for (unsigned i = 0; i < CS.arg_size(); ++i)
|
|
if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
|
|
Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest
|
|
: CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
|
|
cpyDest->getName(), C);
|
|
changedArgument = true;
|
|
if (CS.getArgument(i)->getType() == Dest->getType())
|
|
CS.setArgument(i, Dest);
|
|
else
|
|
CS.setArgument(i, CastInst::CreatePointerCast(Dest,
|
|
CS.getArgument(i)->getType(), Dest->getName(), C));
|
|
}
|
|
|
|
if (!changedArgument)
|
|
return false;
|
|
|
|
// If the destination wasn't sufficiently aligned then increase its alignment.
|
|
if (!isDestSufficientlyAligned) {
|
|
assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!");
|
|
cast<AllocaInst>(cpyDest)->setAlignment(MaybeAlign(srcAlign));
|
|
}
|
|
|
|
// Drop any cached information about the call, because we may have changed
|
|
// its dependence information by changing its parameter.
|
|
MD->removeInstruction(C);
|
|
|
|
// Update AA metadata
|
|
// FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
|
|
// handled here, but combineMetadata doesn't support them yet
|
|
unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
|
|
LLVMContext::MD_noalias,
|
|
LLVMContext::MD_invariant_group,
|
|
LLVMContext::MD_access_group};
|
|
combineMetadata(C, cpy, KnownIDs, true);
|
|
|
|
// Remove the memcpy.
|
|
MD->removeInstruction(cpy);
|
|
++NumMemCpyInstr;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// We've found that the (upward scanning) memory dependence of memcpy 'M' is
|
|
/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can.
|
|
bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
|
|
MemCpyInst *MDep) {
|
|
// We can only transforms memcpy's where the dest of one is the source of the
|
|
// other.
|
|
if (M->getSource() != MDep->getDest() || MDep->isVolatile())
|
|
return false;
|
|
|
|
// If dep instruction is reading from our current input, then it is a noop
|
|
// transfer and substituting the input won't change this instruction. Just
|
|
// ignore the input and let someone else zap MDep. This handles cases like:
|
|
// memcpy(a <- a)
|
|
// memcpy(b <- a)
|
|
if (M->getSource() == MDep->getSource())
|
|
return false;
|
|
|
|
// Second, the length of the memcpy's must be the same, or the preceding one
|
|
// must be larger than the following one.
|
|
ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
|
|
ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength());
|
|
if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
|
|
return false;
|
|
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
|
|
// Verify that the copied-from memory doesn't change in between the two
|
|
// transfers. For example, in:
|
|
// memcpy(a <- b)
|
|
// *b = 42;
|
|
// memcpy(c <- a)
|
|
// It would be invalid to transform the second memcpy into memcpy(c <- b).
|
|
//
|
|
// TODO: If the code between M and MDep is transparent to the destination "c",
|
|
// then we could still perform the xform by moving M up to the first memcpy.
|
|
//
|
|
// NOTE: This is conservative, it will stop on any read from the source loc,
|
|
// not just the defining memcpy.
|
|
MemDepResult SourceDep =
|
|
MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
|
|
M->getIterator(), M->getParent());
|
|
if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
|
|
return false;
|
|
|
|
// If the dest of the second might alias the source of the first, then the
|
|
// source and dest might overlap. We still want to eliminate the intermediate
|
|
// value, but we have to generate a memmove instead of memcpy.
|
|
bool UseMemMove = false;
|
|
if (!AA.isNoAlias(MemoryLocation::getForDest(M),
|
|
MemoryLocation::getForSource(MDep)))
|
|
UseMemMove = true;
|
|
|
|
// If all checks passed, then we can transform M.
|
|
LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
|
|
<< *MDep << '\n' << *M << '\n');
|
|
|
|
// TODO: Is this worth it if we're creating a less aligned memcpy? For
|
|
// example we could be moving from movaps -> movq on x86.
|
|
IRBuilder<> Builder(M);
|
|
if (UseMemMove)
|
|
Builder.CreateMemMove(M->getRawDest(), M->getDestAlign(),
|
|
MDep->getRawSource(), MDep->getSourceAlign(),
|
|
M->getLength(), M->isVolatile());
|
|
else
|
|
Builder.CreateMemCpy(M->getRawDest(), M->getDestAlign(),
|
|
MDep->getRawSource(), MDep->getSourceAlign(),
|
|
M->getLength(), M->isVolatile());
|
|
|
|
// Remove the instruction we're replacing.
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
++NumMemCpyInstr;
|
|
return true;
|
|
}
|
|
|
|
/// We've found that the (upward scanning) memory dependence of \p MemCpy is
|
|
/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that
|
|
/// weren't copied over by \p MemCpy.
|
|
///
|
|
/// In other words, transform:
|
|
/// \code
|
|
/// memset(dst, c, dst_size);
|
|
/// memcpy(dst, src, src_size);
|
|
/// \endcode
|
|
/// into:
|
|
/// \code
|
|
/// memcpy(dst, src, src_size);
|
|
/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
|
|
/// \endcode
|
|
bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
|
|
MemSetInst *MemSet) {
|
|
// We can only transform memset/memcpy with the same destination.
|
|
if (MemSet->getDest() != MemCpy->getDest())
|
|
return false;
|
|
|
|
// Check that there are no other dependencies on the memset destination.
|
|
MemDepResult DstDepInfo =
|
|
MD->getPointerDependencyFrom(MemoryLocation::getForDest(MemSet), false,
|
|
MemCpy->getIterator(), MemCpy->getParent());
|
|
if (DstDepInfo.getInst() != MemSet)
|
|
return false;
|
|
|
|
// Use the same i8* dest as the memcpy, killing the memset dest if different.
|
|
Value *Dest = MemCpy->getRawDest();
|
|
Value *DestSize = MemSet->getLength();
|
|
Value *SrcSize = MemCpy->getLength();
|
|
|
|
// By default, create an unaligned memset.
|
|
unsigned Align = 1;
|
|
// If Dest is aligned, and SrcSize is constant, use the minimum alignment
|
|
// of the sum.
|
|
const unsigned DestAlign =
|
|
std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment());
|
|
if (DestAlign > 1)
|
|
if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
|
|
Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
|
|
|
|
IRBuilder<> Builder(MemCpy);
|
|
|
|
// If the sizes have different types, zext the smaller one.
|
|
if (DestSize->getType() != SrcSize->getType()) {
|
|
if (DestSize->getType()->getIntegerBitWidth() >
|
|
SrcSize->getType()->getIntegerBitWidth())
|
|
SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType());
|
|
else
|
|
DestSize = Builder.CreateZExt(DestSize, SrcSize->getType());
|
|
}
|
|
|
|
Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize);
|
|
Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize);
|
|
Value *MemsetLen = Builder.CreateSelect(
|
|
Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff);
|
|
Builder.CreateMemSet(
|
|
Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest,
|
|
SrcSize),
|
|
MemSet->getOperand(1), MemsetLen, MaybeAlign(Align));
|
|
|
|
MD->removeInstruction(MemSet);
|
|
MemSet->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
/// Determine whether the instruction has undefined content for the given Size,
|
|
/// either because it was freshly alloca'd or started its lifetime.
|
|
static bool hasUndefContents(Instruction *I, ConstantInt *Size) {
|
|
if (isa<AllocaInst>(I))
|
|
return true;
|
|
|
|
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
|
|
if (II->getIntrinsicID() == Intrinsic::lifetime_start)
|
|
if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
|
|
if (LTSize->getZExtValue() >= Size->getZExtValue())
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Transform memcpy to memset when its source was just memset.
|
|
/// In other words, turn:
|
|
/// \code
|
|
/// memset(dst1, c, dst1_size);
|
|
/// memcpy(dst2, dst1, dst2_size);
|
|
/// \endcode
|
|
/// into:
|
|
/// \code
|
|
/// memset(dst1, c, dst1_size);
|
|
/// memset(dst2, c, dst2_size);
|
|
/// \endcode
|
|
/// When dst2_size <= dst1_size.
|
|
///
|
|
/// The \p MemCpy must have a Constant length.
|
|
bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy,
|
|
MemSetInst *MemSet) {
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
|
|
// Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
|
|
// memcpying from the same address. Otherwise it is hard to reason about.
|
|
if (!AA.isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
|
|
return false;
|
|
|
|
// A known memset size is required.
|
|
ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
|
|
if (!MemSetSize)
|
|
return false;
|
|
|
|
// Make sure the memcpy doesn't read any more than what the memset wrote.
|
|
// Don't worry about sizes larger than i64.
|
|
ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
|
|
if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) {
|
|
// If the memcpy is larger than the memset, but the memory was undef prior
|
|
// to the memset, we can just ignore the tail. Technically we're only
|
|
// interested in the bytes from MemSetSize..CopySize here, but as we can't
|
|
// easily represent this location, we use the full 0..CopySize range.
|
|
MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy);
|
|
MemDepResult DepInfo = MD->getPointerDependencyFrom(
|
|
MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent());
|
|
if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize))
|
|
CopySize = MemSetSize;
|
|
else
|
|
return false;
|
|
}
|
|
|
|
IRBuilder<> Builder(MemCpy);
|
|
Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1), CopySize,
|
|
MaybeAlign(MemCpy->getDestAlignment()));
|
|
return true;
|
|
}
|
|
|
|
/// Perform simplification of memcpy's. If we have memcpy A
|
|
/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
|
|
/// B to be a memcpy from X to Z (or potentially a memmove, depending on
|
|
/// circumstances). This allows later passes to remove the first memcpy
|
|
/// altogether.
|
|
bool MemCpyOptPass::processMemCpy(MemCpyInst *M) {
|
|
// We can only optimize non-volatile memcpy's.
|
|
if (M->isVolatile()) return false;
|
|
|
|
// If the source and destination of the memcpy are the same, then zap it.
|
|
if (M->getSource() == M->getDest()) {
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
return false;
|
|
}
|
|
|
|
// If copying from a constant, try to turn the memcpy into a memset.
|
|
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource()))
|
|
if (GV->isConstant() && GV->hasDefinitiveInitializer())
|
|
if (Value *ByteVal = isBytewiseValue(GV->getInitializer(),
|
|
M->getModule()->getDataLayout())) {
|
|
IRBuilder<> Builder(M);
|
|
Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
|
|
MaybeAlign(M->getDestAlignment()), false);
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
++NumCpyToSet;
|
|
return true;
|
|
}
|
|
|
|
MemDepResult DepInfo = MD->getDependency(M);
|
|
|
|
// Try to turn a partially redundant memset + memcpy into
|
|
// memcpy + smaller memset. We don't need the memcpy size for this.
|
|
if (DepInfo.isClobber())
|
|
if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst()))
|
|
if (processMemSetMemCpyDependence(M, MDep))
|
|
return true;
|
|
|
|
// The optimizations after this point require the memcpy size.
|
|
ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
|
|
if (!CopySize) return false;
|
|
|
|
// There are four possible optimizations we can do for memcpy:
|
|
// a) memcpy-memcpy xform which exposes redundance for DSE.
|
|
// b) call-memcpy xform for return slot optimization.
|
|
// c) memcpy from freshly alloca'd space or space that has just started its
|
|
// lifetime copies undefined data, and we can therefore eliminate the
|
|
// memcpy in favor of the data that was already at the destination.
|
|
// d) memcpy from a just-memset'd source can be turned into memset.
|
|
if (DepInfo.isClobber()) {
|
|
if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
|
|
// FIXME: Can we pass in either of dest/src alignment here instead
|
|
// of conservatively taking the minimum?
|
|
unsigned Align = MinAlign(M->getDestAlignment(), M->getSourceAlignment());
|
|
if (performCallSlotOptzn(M, M->getDest(), M->getSource(),
|
|
CopySize->getZExtValue(), Align,
|
|
C)) {
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
MemoryLocation SrcLoc = MemoryLocation::getForSource(M);
|
|
MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
|
|
SrcLoc, true, M->getIterator(), M->getParent());
|
|
|
|
if (SrcDepInfo.isClobber()) {
|
|
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
|
|
return processMemCpyMemCpyDependence(M, MDep);
|
|
} else if (SrcDepInfo.isDef()) {
|
|
if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) {
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
++NumMemCpyInstr;
|
|
return true;
|
|
}
|
|
}
|
|
|
|
if (SrcDepInfo.isClobber())
|
|
if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
|
|
if (performMemCpyToMemSetOptzn(M, MDep)) {
|
|
MD->removeInstruction(M);
|
|
M->eraseFromParent();
|
|
++NumCpyToSet;
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
|
|
/// not to alias.
|
|
bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
|
|
AliasAnalysis &AA = LookupAliasAnalysis();
|
|
|
|
if (!TLI->has(LibFunc_memmove))
|
|
return false;
|
|
|
|
// See if the pointers alias.
|
|
if (!AA.isNoAlias(MemoryLocation::getForDest(M),
|
|
MemoryLocation::getForSource(M)))
|
|
return false;
|
|
|
|
LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M
|
|
<< "\n");
|
|
|
|
// If not, then we know we can transform this.
|
|
Type *ArgTys[3] = { M->getRawDest()->getType(),
|
|
M->getRawSource()->getType(),
|
|
M->getLength()->getType() };
|
|
M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(),
|
|
Intrinsic::memcpy, ArgTys));
|
|
|
|
// MemDep may have over conservative information about this instruction, just
|
|
// conservatively flush it from the cache.
|
|
MD->removeInstruction(M);
|
|
|
|
++NumMoveToCpy;
|
|
return true;
|
|
}
|
|
|
|
/// This is called on every byval argument in call sites.
|
|
bool MemCpyOptPass::processByValArgument(CallSite CS, unsigned ArgNo) {
|
|
const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout();
|
|
// Find out what feeds this byval argument.
|
|
Value *ByValArg = CS.getArgument(ArgNo);
|
|
Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType();
|
|
uint64_t ByValSize = DL.getTypeAllocSize(ByValTy);
|
|
MemDepResult DepInfo = MD->getPointerDependencyFrom(
|
|
MemoryLocation(ByValArg, LocationSize::precise(ByValSize)), true,
|
|
CS.getInstruction()->getIterator(), CS.getInstruction()->getParent());
|
|
if (!DepInfo.isClobber())
|
|
return false;
|
|
|
|
// If the byval argument isn't fed by a memcpy, ignore it. If it is fed by
|
|
// a memcpy, see if we can byval from the source of the memcpy instead of the
|
|
// result.
|
|
MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst());
|
|
if (!MDep || MDep->isVolatile() ||
|
|
ByValArg->stripPointerCasts() != MDep->getDest())
|
|
return false;
|
|
|
|
// The length of the memcpy must be larger or equal to the size of the byval.
|
|
ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
|
|
if (!C1 || C1->getValue().getZExtValue() < ByValSize)
|
|
return false;
|
|
|
|
// Get the alignment of the byval. If the call doesn't specify the alignment,
|
|
// then it is some target specific value that we can't know.
|
|
unsigned ByValAlign = CS.getParamAlignment(ArgNo);
|
|
if (ByValAlign == 0) return false;
|
|
|
|
// If it is greater than the memcpy, then we check to see if we can force the
|
|
// source of the memcpy to the alignment we need. If we fail, we bail out.
|
|
AssumptionCache &AC = LookupAssumptionCache();
|
|
DominatorTree &DT = LookupDomTree();
|
|
if (MDep->getSourceAlignment() < ByValAlign &&
|
|
getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL,
|
|
CS.getInstruction(), &AC, &DT) < ByValAlign)
|
|
return false;
|
|
|
|
// The address space of the memcpy source must match the byval argument
|
|
if (MDep->getSource()->getType()->getPointerAddressSpace() !=
|
|
ByValArg->getType()->getPointerAddressSpace())
|
|
return false;
|
|
|
|
// Verify that the copied-from memory doesn't change in between the memcpy and
|
|
// the byval call.
|
|
// memcpy(a <- b)
|
|
// *b = 42;
|
|
// foo(*a)
|
|
// It would be invalid to transform the second memcpy into foo(*b).
|
|
//
|
|
// NOTE: This is conservative, it will stop on any read from the source loc,
|
|
// not just the defining memcpy.
|
|
MemDepResult SourceDep = MD->getPointerDependencyFrom(
|
|
MemoryLocation::getForSource(MDep), false,
|
|
CS.getInstruction()->getIterator(), MDep->getParent());
|
|
if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
|
|
return false;
|
|
|
|
Value *TmpCast = MDep->getSource();
|
|
if (MDep->getSource()->getType() != ByValArg->getType())
|
|
TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
|
|
"tmpcast", CS.getInstruction());
|
|
|
|
LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
|
|
<< " " << *MDep << "\n"
|
|
<< " " << *CS.getInstruction() << "\n");
|
|
|
|
// Otherwise we're good! Update the byval argument.
|
|
CS.setArgument(ArgNo, TmpCast);
|
|
++NumMemCpyInstr;
|
|
return true;
|
|
}
|
|
|
|
/// Executes one iteration of MemCpyOptPass.
|
|
bool MemCpyOptPass::iterateOnFunction(Function &F) {
|
|
bool MadeChange = false;
|
|
|
|
DominatorTree &DT = LookupDomTree();
|
|
|
|
// Walk all instruction in the function.
|
|
for (BasicBlock &BB : F) {
|
|
// Skip unreachable blocks. For example processStore assumes that an
|
|
// instruction in a BB can't be dominated by a later instruction in the
|
|
// same BB (which is a scenario that can happen for an unreachable BB that
|
|
// has itself as a predecessor).
|
|
if (!DT.isReachableFromEntry(&BB))
|
|
continue;
|
|
|
|
for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
|
|
// Avoid invalidating the iterator.
|
|
Instruction *I = &*BI++;
|
|
|
|
bool RepeatInstruction = false;
|
|
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(I))
|
|
MadeChange |= processStore(SI, BI);
|
|
else if (MemSetInst *M = dyn_cast<MemSetInst>(I))
|
|
RepeatInstruction = processMemSet(M, BI);
|
|
else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
|
|
RepeatInstruction = processMemCpy(M);
|
|
else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I))
|
|
RepeatInstruction = processMemMove(M);
|
|
else if (auto CS = CallSite(I)) {
|
|
for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
|
|
if (CS.isByValArgument(i))
|
|
MadeChange |= processByValArgument(CS, i);
|
|
}
|
|
|
|
// Reprocess the instruction if desired.
|
|
if (RepeatInstruction) {
|
|
if (BI != BB.begin())
|
|
--BI;
|
|
MadeChange = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) {
|
|
auto &MD = AM.getResult<MemoryDependenceAnalysis>(F);
|
|
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
|
|
|
|
auto LookupAliasAnalysis = [&]() -> AliasAnalysis & {
|
|
return AM.getResult<AAManager>(F);
|
|
};
|
|
auto LookupAssumptionCache = [&]() -> AssumptionCache & {
|
|
return AM.getResult<AssumptionAnalysis>(F);
|
|
};
|
|
auto LookupDomTree = [&]() -> DominatorTree & {
|
|
return AM.getResult<DominatorTreeAnalysis>(F);
|
|
};
|
|
|
|
bool MadeChange = runImpl(F, &MD, &TLI, LookupAliasAnalysis,
|
|
LookupAssumptionCache, LookupDomTree);
|
|
if (!MadeChange)
|
|
return PreservedAnalyses::all();
|
|
|
|
PreservedAnalyses PA;
|
|
PA.preserveSet<CFGAnalyses>();
|
|
PA.preserve<GlobalsAA>();
|
|
PA.preserve<MemoryDependenceAnalysis>();
|
|
return PA;
|
|
}
|
|
|
|
bool MemCpyOptPass::runImpl(
|
|
Function &F, MemoryDependenceResults *MD_, TargetLibraryInfo *TLI_,
|
|
std::function<AliasAnalysis &()> LookupAliasAnalysis_,
|
|
std::function<AssumptionCache &()> LookupAssumptionCache_,
|
|
std::function<DominatorTree &()> LookupDomTree_) {
|
|
bool MadeChange = false;
|
|
MD = MD_;
|
|
TLI = TLI_;
|
|
LookupAliasAnalysis = std::move(LookupAliasAnalysis_);
|
|
LookupAssumptionCache = std::move(LookupAssumptionCache_);
|
|
LookupDomTree = std::move(LookupDomTree_);
|
|
|
|
// If we don't have at least memset and memcpy, there is little point of doing
|
|
// anything here. These are required by a freestanding implementation, so if
|
|
// even they are disabled, there is no point in trying hard.
|
|
if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
|
|
return false;
|
|
|
|
while (true) {
|
|
if (!iterateOnFunction(F))
|
|
break;
|
|
MadeChange = true;
|
|
}
|
|
|
|
MD = nullptr;
|
|
return MadeChange;
|
|
}
|
|
|
|
/// This is the main transformation entry point for a function.
|
|
bool MemCpyOptLegacyPass::runOnFunction(Function &F) {
|
|
if (skipFunction(F))
|
|
return false;
|
|
|
|
auto *MD = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
|
|
auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
|
|
|
|
auto LookupAliasAnalysis = [this]() -> AliasAnalysis & {
|
|
return getAnalysis<AAResultsWrapperPass>().getAAResults();
|
|
};
|
|
auto LookupAssumptionCache = [this, &F]() -> AssumptionCache & {
|
|
return getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
|
|
};
|
|
auto LookupDomTree = [this]() -> DominatorTree & {
|
|
return getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
};
|
|
|
|
return Impl.runImpl(F, MD, TLI, LookupAliasAnalysis, LookupAssumptionCache,
|
|
LookupDomTree);
|
|
}
|