forked from OSchip/llvm-project
471 lines
17 KiB
C++
471 lines
17 KiB
C++
//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
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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 a simple dominator tree walk that eliminates trivially
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// redundant instructions.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "early-cse"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/RecyclingAllocator.h"
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#include "llvm/ADT/ScopedHashTable.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumSimplify, "Number of instructions simplified or DCE'd");
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STATISTIC(NumCSE, "Number of instructions CSE'd");
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STATISTIC(NumCSELoad, "Number of load instructions CSE'd");
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STATISTIC(NumCSECall, "Number of call instructions CSE'd");
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STATISTIC(NumDSE, "Number of trivial dead stores removed");
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static unsigned getHash(const void *V) {
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return DenseMapInfo<const void*>::getHashValue(V);
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}
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//===----------------------------------------------------------------------===//
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// SimpleValue
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//===----------------------------------------------------------------------===//
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namespace {
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/// SimpleValue - Instances of this struct represent available values in the
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/// scoped hash table.
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struct SimpleValue {
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Instruction *Inst;
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SimpleValue(Instruction *I) : Inst(I) {
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assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
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}
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bool isSentinel() const {
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return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
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Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
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}
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static bool canHandle(Instruction *Inst) {
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// This can only handle non-void readnone functions.
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if (CallInst *CI = dyn_cast<CallInst>(Inst))
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return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
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return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
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isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
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isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
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isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
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isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
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}
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};
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}
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namespace llvm {
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// SimpleValue is POD.
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template<> struct isPodLike<SimpleValue> {
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static const bool value = true;
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};
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template<> struct DenseMapInfo<SimpleValue> {
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static inline SimpleValue getEmptyKey() {
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return DenseMapInfo<Instruction*>::getEmptyKey();
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}
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static inline SimpleValue getTombstoneKey() {
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return DenseMapInfo<Instruction*>::getTombstoneKey();
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}
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static unsigned getHashValue(SimpleValue Val);
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static bool isEqual(SimpleValue LHS, SimpleValue RHS);
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};
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}
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unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
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Instruction *Inst = Val.Inst;
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// Hash in all of the operands as pointers.
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unsigned Res = 0;
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for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
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Res ^= getHash(Inst->getOperand(i)) << (i & 0xF);
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if (CastInst *CI = dyn_cast<CastInst>(Inst))
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Res ^= getHash(CI->getType());
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else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
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Res ^= CI->getPredicate();
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else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
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for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
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E = EVI->idx_end(); I != E; ++I)
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Res ^= *I;
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} else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
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for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
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E = IVI->idx_end(); I != E; ++I)
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Res ^= *I;
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} else {
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// nothing extra to hash in.
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assert((isa<CallInst>(Inst) ||
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isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
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isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
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isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
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"Invalid/unknown instruction");
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}
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// Mix in the opcode.
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return (Res << 1) ^ Inst->getOpcode();
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}
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bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
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Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
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if (LHS.isSentinel() || RHS.isSentinel())
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return LHSI == RHSI;
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if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
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return LHSI->isIdenticalTo(RHSI);
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}
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//===----------------------------------------------------------------------===//
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// CallValue
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//===----------------------------------------------------------------------===//
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namespace {
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/// CallValue - Instances of this struct represent available call values in
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/// the scoped hash table.
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struct CallValue {
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Instruction *Inst;
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CallValue(Instruction *I) : Inst(I) {
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assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
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}
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bool isSentinel() const {
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return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
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Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
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}
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static bool canHandle(Instruction *Inst) {
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// Don't value number anything that returns void.
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if (Inst->getType()->isVoidTy())
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return false;
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CallInst *CI = dyn_cast<CallInst>(Inst);
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if (CI == 0 || !CI->onlyReadsMemory())
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return false;
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return true;
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}
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};
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}
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namespace llvm {
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// CallValue is POD.
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template<> struct isPodLike<CallValue> {
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static const bool value = true;
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};
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template<> struct DenseMapInfo<CallValue> {
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static inline CallValue getEmptyKey() {
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return DenseMapInfo<Instruction*>::getEmptyKey();
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}
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static inline CallValue getTombstoneKey() {
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return DenseMapInfo<Instruction*>::getTombstoneKey();
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}
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static unsigned getHashValue(CallValue Val);
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static bool isEqual(CallValue LHS, CallValue RHS);
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};
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}
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unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) {
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Instruction *Inst = Val.Inst;
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// Hash in all of the operands as pointers.
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unsigned Res = 0;
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for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) {
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assert(!Inst->getOperand(i)->getType()->isMetadataTy() &&
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"Cannot value number calls with metadata operands");
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Res ^= getHash(Inst->getOperand(i)) << (i & 0xF);
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}
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// Mix in the opcode.
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return (Res << 1) ^ Inst->getOpcode();
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}
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bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
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Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
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if (LHS.isSentinel() || RHS.isSentinel())
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return LHSI == RHSI;
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return LHSI->isIdenticalTo(RHSI);
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}
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//===----------------------------------------------------------------------===//
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// EarlyCSE pass.
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//===----------------------------------------------------------------------===//
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namespace {
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/// EarlyCSE - This pass does a simple depth-first walk over the dominator
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/// tree, eliminating trivially redundant instructions and using instsimplify
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/// to canonicalize things as it goes. It is intended to be fast and catch
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/// obvious cases so that instcombine and other passes are more effective. It
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/// is expected that a later pass of GVN will catch the interesting/hard
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/// cases.
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class EarlyCSE : public FunctionPass {
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public:
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const TargetData *TD;
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DominatorTree *DT;
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typedef RecyclingAllocator<BumpPtrAllocator,
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ScopedHashTableVal<SimpleValue, Value*> > AllocatorTy;
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typedef ScopedHashTable<SimpleValue, Value*, DenseMapInfo<SimpleValue>,
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AllocatorTy> ScopedHTType;
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/// AvailableValues - This scoped hash table contains the current values of
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/// all of our simple scalar expressions. As we walk down the domtree, we
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/// look to see if instructions are in this: if so, we replace them with what
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/// we find, otherwise we insert them so that dominated values can succeed in
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/// their lookup.
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ScopedHTType *AvailableValues;
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/// AvailableLoads - This scoped hash table contains the current values
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/// of loads. This allows us to get efficient access to dominating loads when
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/// we have a fully redundant load. In addition to the most recent load, we
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/// keep track of a generation count of the read, which is compared against
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/// the current generation count. The current generation count is
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/// incremented after every possibly writing memory operation, which ensures
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/// that we only CSE loads with other loads that have no intervening store.
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typedef RecyclingAllocator<BumpPtrAllocator,
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ScopedHashTableVal<Value*, std::pair<Value*, unsigned> > > LoadMapAllocator;
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typedef ScopedHashTable<Value*, std::pair<Value*, unsigned>,
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DenseMapInfo<Value*>, LoadMapAllocator> LoadHTType;
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LoadHTType *AvailableLoads;
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/// AvailableCalls - This scoped hash table contains the current values
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/// of read-only call values. It uses the same generation count as loads.
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typedef ScopedHashTable<CallValue, std::pair<Value*, unsigned> > CallHTType;
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CallHTType *AvailableCalls;
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/// CurrentGeneration - This is the current generation of the memory value.
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unsigned CurrentGeneration;
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static char ID;
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explicit EarlyCSE() : FunctionPass(ID) {
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initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F);
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private:
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bool processNode(DomTreeNode *Node);
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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.addRequired<DominatorTree>();
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AU.setPreservesCFG();
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}
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};
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}
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char EarlyCSE::ID = 0;
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// createEarlyCSEPass - The public interface to this file.
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FunctionPass *llvm::createEarlyCSEPass() {
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return new EarlyCSE();
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}
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INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTree)
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INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
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bool EarlyCSE::processNode(DomTreeNode *Node) {
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// Define a scope in the scoped hash table. When we are done processing this
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// domtree node and recurse back up to our parent domtree node, this will pop
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// off all the values we install.
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ScopedHTType::ScopeTy Scope(*AvailableValues);
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// Define a scope for the load values so that anything we add will get
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// popped when we recurse back up to our parent domtree node.
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LoadHTType::ScopeTy LoadScope(*AvailableLoads);
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// Define a scope for the call values so that anything we add will get
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// popped when we recurse back up to our parent domtree node.
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CallHTType::ScopeTy CallScope(*AvailableCalls);
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BasicBlock *BB = Node->getBlock();
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// If this block has a single predecessor, then the predecessor is the parent
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// of the domtree node and all of the live out memory values are still current
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// in this block. If this block has multiple predecessors, then they could
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// have invalidated the live-out memory values of our parent value. For now,
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// just be conservative and invalidate memory if this block has multiple
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// predecessors.
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if (BB->getSinglePredecessor() == 0)
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++CurrentGeneration;
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/// LastStore - Keep track of the last non-volatile store that we saw... for
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/// as long as there in no instruction that reads memory. If we see a store
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/// to the same location, we delete the dead store. This zaps trivial dead
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/// stores which can occur in bitfield code among other things.
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StoreInst *LastStore = 0;
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bool Changed = false;
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// See if any instructions in the block can be eliminated. If so, do it. If
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// not, add them to AvailableValues.
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
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Instruction *Inst = I++;
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// Dead instructions should just be removed.
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if (isInstructionTriviallyDead(Inst)) {
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DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
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Inst->eraseFromParent();
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Changed = true;
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++NumSimplify;
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continue;
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}
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// If the instruction can be simplified (e.g. X+0 = X) then replace it with
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// its simpler value.
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if (Value *V = SimplifyInstruction(Inst, TD, DT)) {
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DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
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Inst->replaceAllUsesWith(V);
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Inst->eraseFromParent();
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Changed = true;
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++NumSimplify;
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continue;
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}
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// If this is a simple instruction that we can value number, process it.
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if (SimpleValue::canHandle(Inst)) {
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// See if the instruction has an available value. If so, use it.
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if (Value *V = AvailableValues->lookup(Inst)) {
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DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
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Inst->replaceAllUsesWith(V);
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Inst->eraseFromParent();
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Changed = true;
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++NumCSE;
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continue;
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}
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// Otherwise, just remember that this value is available.
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AvailableValues->insert(Inst, Inst);
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continue;
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}
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// If this is a non-volatile load, process it.
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
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// Ignore volatile loads.
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if (!LI->isSimple()) {
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LastStore = 0;
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continue;
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}
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// If we have an available version of this load, and if it is the right
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// generation, replace this instruction.
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std::pair<Value*, unsigned> InVal =
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AvailableLoads->lookup(Inst->getOperand(0));
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if (InVal.first != 0 && InVal.second == CurrentGeneration) {
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DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst << " to: "
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<< *InVal.first << '\n');
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if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
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Inst->eraseFromParent();
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Changed = true;
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++NumCSELoad;
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continue;
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}
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// Otherwise, remember that we have this instruction.
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AvailableLoads->insert(Inst->getOperand(0),
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std::pair<Value*, unsigned>(Inst, CurrentGeneration));
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LastStore = 0;
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continue;
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}
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// If this instruction may read from memory, forget LastStore.
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if (Inst->mayReadFromMemory())
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LastStore = 0;
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// If this is a read-only call, process it.
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if (CallValue::canHandle(Inst)) {
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// If we have an available version of this call, and if it is the right
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// generation, replace this instruction.
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std::pair<Value*, unsigned> InVal = AvailableCalls->lookup(Inst);
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if (InVal.first != 0 && InVal.second == CurrentGeneration) {
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DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst << " to: "
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<< *InVal.first << '\n');
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if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
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Inst->eraseFromParent();
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Changed = true;
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++NumCSECall;
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continue;
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}
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// Otherwise, remember that we have this instruction.
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AvailableCalls->insert(Inst,
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std::pair<Value*, unsigned>(Inst, CurrentGeneration));
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continue;
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}
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// Okay, this isn't something we can CSE at all. Check to see if it is
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// something that could modify memory. If so, our available memory values
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// cannot be used so bump the generation count.
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if (Inst->mayWriteToMemory()) {
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++CurrentGeneration;
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if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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// We do a trivial form of DSE if there are two stores to the same
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// location with no intervening loads. Delete the earlier store.
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if (LastStore &&
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LastStore->getPointerOperand() == SI->getPointerOperand()) {
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DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore << " due to: "
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<< *Inst << '\n');
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LastStore->eraseFromParent();
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Changed = true;
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++NumDSE;
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LastStore = 0;
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continue;
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}
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// Okay, we just invalidated anything we knew about loaded values. Try
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// to salvage *something* by remembering that the stored value is a live
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// version of the pointer. It is safe to forward from volatile stores
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// to non-volatile loads, so we don't have to check for volatility of
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// the store.
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AvailableLoads->insert(SI->getPointerOperand(),
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std::pair<Value*, unsigned>(SI->getValueOperand(), CurrentGeneration));
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// Remember that this was the last store we saw for DSE.
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if (SI->isSimple())
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LastStore = SI;
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}
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}
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}
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unsigned LiveOutGeneration = CurrentGeneration;
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for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I) {
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Changed |= processNode(*I);
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// Pop any generation changes off the stack from the recursive walk.
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CurrentGeneration = LiveOutGeneration;
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}
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return Changed;
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}
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bool EarlyCSE::runOnFunction(Function &F) {
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TD = getAnalysisIfAvailable<TargetData>();
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DT = &getAnalysis<DominatorTree>();
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// Tables that the pass uses when walking the domtree.
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ScopedHTType AVTable;
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AvailableValues = &AVTable;
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LoadHTType LoadTable;
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AvailableLoads = &LoadTable;
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CallHTType CallTable;
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AvailableCalls = &CallTable;
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CurrentGeneration = 0;
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return processNode(DT->getRootNode());
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}
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