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cd52a7a381
Apparently, the style needs to be agreed upon first. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240390 91177308-0d34-0410-b5e6-96231b3b80d8
780 lines
29 KiB
C++
780 lines
29 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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#include "llvm/Transforms/Scalar/EarlyCSE.h"
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#include "llvm/ADT/Hashing.h"
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#include "llvm/ADT/ScopedHashTable.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.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/PatternMatch.h"
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#include "llvm/Pass.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/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 <deque>
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using namespace llvm;
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using namespace llvm::PatternMatch;
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#define DEBUG_TYPE "early-cse"
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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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//===----------------------------------------------------------------------===//
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// SimpleValue
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//===----------------------------------------------------------------------===//
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namespace {
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/// \brief Struct representing the available values in the 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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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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if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Inst)) {
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Value *LHS = BinOp->getOperand(0);
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Value *RHS = BinOp->getOperand(1);
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if (BinOp->isCommutative() && BinOp->getOperand(0) > BinOp->getOperand(1))
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std::swap(LHS, RHS);
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if (isa<OverflowingBinaryOperator>(BinOp)) {
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// Hash the overflow behavior
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unsigned Overflow =
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BinOp->hasNoSignedWrap() * OverflowingBinaryOperator::NoSignedWrap |
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BinOp->hasNoUnsignedWrap() *
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OverflowingBinaryOperator::NoUnsignedWrap;
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return hash_combine(BinOp->getOpcode(), Overflow, LHS, RHS);
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}
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return hash_combine(BinOp->getOpcode(), LHS, RHS);
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}
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if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) {
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Value *LHS = CI->getOperand(0);
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Value *RHS = CI->getOperand(1);
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CmpInst::Predicate Pred = CI->getPredicate();
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if (Inst->getOperand(0) > Inst->getOperand(1)) {
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std::swap(LHS, RHS);
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Pred = CI->getSwappedPredicate();
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}
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return hash_combine(Inst->getOpcode(), Pred, LHS, RHS);
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}
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if (CastInst *CI = dyn_cast<CastInst>(Inst))
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return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0));
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if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst))
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return hash_combine(EVI->getOpcode(), EVI->getOperand(0),
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hash_combine_range(EVI->idx_begin(), EVI->idx_end()));
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if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst))
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return hash_combine(IVI->getOpcode(), IVI->getOperand(0),
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IVI->getOperand(1),
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hash_combine_range(IVI->idx_begin(), IVI->idx_end()));
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assert((isa<CallInst>(Inst) || isa<BinaryOperator>(Inst) ||
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isa<GetElementPtrInst>(Inst) || isa<SelectInst>(Inst) ||
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isa<ExtractElementInst>(Inst) || isa<InsertElementInst>(Inst) ||
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isa<ShuffleVectorInst>(Inst)) &&
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"Invalid/unknown instruction");
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// Mix in the opcode.
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return hash_combine(
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Inst->getOpcode(),
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hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
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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())
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return false;
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if (LHSI->isIdenticalTo(RHSI))
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return true;
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// If we're not strictly identical, we still might be a commutable instruction
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if (BinaryOperator *LHSBinOp = dyn_cast<BinaryOperator>(LHSI)) {
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if (!LHSBinOp->isCommutative())
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return false;
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assert(isa<BinaryOperator>(RHSI) &&
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"same opcode, but different instruction type?");
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BinaryOperator *RHSBinOp = cast<BinaryOperator>(RHSI);
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// Check overflow attributes
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if (isa<OverflowingBinaryOperator>(LHSBinOp)) {
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assert(isa<OverflowingBinaryOperator>(RHSBinOp) &&
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"same opcode, but different operator type?");
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if (LHSBinOp->hasNoUnsignedWrap() != RHSBinOp->hasNoUnsignedWrap() ||
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LHSBinOp->hasNoSignedWrap() != RHSBinOp->hasNoSignedWrap())
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return false;
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}
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// Commuted equality
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return LHSBinOp->getOperand(0) == RHSBinOp->getOperand(1) &&
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LHSBinOp->getOperand(1) == RHSBinOp->getOperand(0);
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}
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if (CmpInst *LHSCmp = dyn_cast<CmpInst>(LHSI)) {
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assert(isa<CmpInst>(RHSI) &&
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"same opcode, but different instruction type?");
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CmpInst *RHSCmp = cast<CmpInst>(RHSI);
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// Commuted equality
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return LHSCmp->getOperand(0) == RHSCmp->getOperand(1) &&
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LHSCmp->getOperand(1) == RHSCmp->getOperand(0) &&
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LHSCmp->getSwappedPredicate() == RHSCmp->getPredicate();
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}
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return false;
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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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/// \brief Struct representing the available call values in the scoped hash
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/// 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 || !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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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 all of the operands as pointers and mix in the opcode.
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return hash_combine(
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Inst->getOpcode(),
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hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
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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 implementation
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//===----------------------------------------------------------------------===//
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namespace {
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/// \brief A simple and fast domtree-based CSE pass.
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///
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/// This pass does a simple depth-first walk over the dominator tree,
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/// eliminating trivially redundant instructions and using instsimplify to
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/// canonicalize things as it goes. It is intended to be fast and catch obvious
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/// cases so that instcombine and other passes are more effective. It is
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/// expected that a later pass of GVN will catch the interesting/hard cases.
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class EarlyCSE {
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public:
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Function &F;
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const TargetLibraryInfo &TLI;
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const TargetTransformInfo &TTI;
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DominatorTree &DT;
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AssumptionCache &AC;
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typedef RecyclingAllocator<
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BumpPtrAllocator, ScopedHashTableVal<SimpleValue, Value *>> AllocatorTy;
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typedef ScopedHashTable<SimpleValue, Value *, DenseMapInfo<SimpleValue>,
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AllocatorTy> ScopedHTType;
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/// \brief A scoped hash table of the current values of all of our simple
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/// scalar expressions.
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///
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/// As we walk down the domtree, we look to see if instructions are in this:
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/// if so, we replace them with what we find, otherwise we insert them so
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/// that dominated values can succeed in their lookup.
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ScopedHTType AvailableValues;
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/// \brief A scoped hash table of the current values of loads.
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///
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/// This allows us to get efficient access to dominating loads when we have
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/// a fully redundant load. In addition to the most recent load, we keep
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/// track of a generation count of the read, which is compared against the
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/// current generation count. The current generation count is incremented
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/// after every possibly writing memory operation, which ensures that we only
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/// CSE loads with other loads that have no intervening store.
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typedef RecyclingAllocator<
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BumpPtrAllocator,
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ScopedHashTableVal<Value *, std::pair<Value *, unsigned>>>
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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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/// \brief A scoped hash table of the current values of read-only call
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/// values.
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///
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/// 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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/// \brief This is the current generation of the memory value.
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unsigned CurrentGeneration;
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/// \brief Set up the EarlyCSE runner for a particular function.
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EarlyCSE(Function &F, const TargetLibraryInfo &TLI,
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const TargetTransformInfo &TTI, DominatorTree &DT,
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AssumptionCache &AC)
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: F(F), TLI(TLI), TTI(TTI), DT(DT), AC(AC), CurrentGeneration(0) {}
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bool run();
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private:
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// Almost a POD, but needs to call the constructors for the scoped hash
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// tables so that a new scope gets pushed on. These are RAII so that the
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// scope gets popped when the NodeScope is destroyed.
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class NodeScope {
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public:
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NodeScope(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
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CallHTType &AvailableCalls)
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: Scope(AvailableValues), LoadScope(AvailableLoads),
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CallScope(AvailableCalls) {}
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private:
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NodeScope(const NodeScope &) = delete;
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void operator=(const NodeScope &) = delete;
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ScopedHTType::ScopeTy Scope;
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LoadHTType::ScopeTy LoadScope;
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CallHTType::ScopeTy CallScope;
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};
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// Contains all the needed information to create a stack for doing a depth
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// first tranversal of the tree. This includes scopes for values, loads, and
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// calls as well as the generation. There is a child iterator so that the
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// children do not need to be store spearately.
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class StackNode {
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public:
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StackNode(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
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CallHTType &AvailableCalls, unsigned cg, DomTreeNode *n,
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DomTreeNode::iterator child, DomTreeNode::iterator end)
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: CurrentGeneration(cg), ChildGeneration(cg), Node(n), ChildIter(child),
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EndIter(end), Scopes(AvailableValues, AvailableLoads, AvailableCalls),
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Processed(false) {}
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// Accessors.
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unsigned currentGeneration() { return CurrentGeneration; }
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unsigned childGeneration() { return ChildGeneration; }
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void childGeneration(unsigned generation) { ChildGeneration = generation; }
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DomTreeNode *node() { return Node; }
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DomTreeNode::iterator childIter() { return ChildIter; }
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DomTreeNode *nextChild() {
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DomTreeNode *child = *ChildIter;
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++ChildIter;
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return child;
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}
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DomTreeNode::iterator end() { return EndIter; }
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bool isProcessed() { return Processed; }
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void process() { Processed = true; }
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private:
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StackNode(const StackNode &) = delete;
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void operator=(const StackNode &) = delete;
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// Members.
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unsigned CurrentGeneration;
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unsigned ChildGeneration;
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DomTreeNode *Node;
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DomTreeNode::iterator ChildIter;
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DomTreeNode::iterator EndIter;
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NodeScope Scopes;
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bool Processed;
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};
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/// \brief Wrapper class to handle memory instructions, including loads,
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/// stores and intrinsic loads and stores defined by the target.
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class ParseMemoryInst {
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public:
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ParseMemoryInst(Instruction *Inst, const TargetTransformInfo &TTI)
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: Load(false), Store(false), Vol(false), MayReadFromMemory(false),
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MayWriteToMemory(false), MatchingId(-1), Ptr(nullptr) {
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MayReadFromMemory = Inst->mayReadFromMemory();
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MayWriteToMemory = Inst->mayWriteToMemory();
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
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MemIntrinsicInfo Info;
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if (!TTI.getTgtMemIntrinsic(II, Info))
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return;
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if (Info.NumMemRefs == 1) {
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Store = Info.WriteMem;
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Load = Info.ReadMem;
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MatchingId = Info.MatchingId;
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MayReadFromMemory = Info.ReadMem;
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MayWriteToMemory = Info.WriteMem;
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Vol = Info.Vol;
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Ptr = Info.PtrVal;
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}
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} else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
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Load = true;
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Vol = !LI->isSimple();
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Ptr = LI->getPointerOperand();
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} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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Store = true;
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Vol = !SI->isSimple();
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Ptr = SI->getPointerOperand();
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}
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}
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bool isLoad() { return Load; }
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bool isStore() { return Store; }
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bool isVolatile() { return Vol; }
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bool isMatchingMemLoc(const ParseMemoryInst &Inst) {
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return Ptr == Inst.Ptr && MatchingId == Inst.MatchingId;
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}
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bool isValid() { return Ptr != nullptr; }
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int getMatchingId() { return MatchingId; }
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Value *getPtr() { return Ptr; }
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bool mayReadFromMemory() { return MayReadFromMemory; }
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bool mayWriteToMemory() { return MayWriteToMemory; }
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private:
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bool Load;
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bool Store;
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bool Vol;
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bool MayReadFromMemory;
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bool MayWriteToMemory;
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// For regular (non-intrinsic) loads/stores, this is set to -1. For
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// intrinsic loads/stores, the id is retrieved from the corresponding
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// field in the MemIntrinsicInfo structure. That field contains
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// non-negative values only.
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int MatchingId;
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Value *Ptr;
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};
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bool processNode(DomTreeNode *Node);
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Value *getOrCreateResult(Value *Inst, Type *ExpectedType) const {
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
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return LI;
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else if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
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return SI->getValueOperand();
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assert(isa<IntrinsicInst>(Inst) && "Instruction not supported");
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return TTI.getOrCreateResultFromMemIntrinsic(cast<IntrinsicInst>(Inst),
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ExpectedType);
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}
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};
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}
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bool EarlyCSE::processNode(DomTreeNode *Node) {
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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())
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++CurrentGeneration;
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// If this node has a single predecessor which ends in a conditional branch,
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// we can infer the value of the branch condition given that we took this
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// path. We need the single predeccesor to ensure there's not another path
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// which reaches this block where the condition might hold a different
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// value. Since we're adding this to the scoped hash table (like any other
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// def), it will have been popped if we encounter a future merge block.
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if (BasicBlock *Pred = BB->getSinglePredecessor())
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if (auto *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
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if (BI->isConditional())
|
|
if (auto *CondInst = dyn_cast<Instruction>(BI->getCondition()))
|
|
if (SimpleValue::canHandle(CondInst)) {
|
|
assert(BI->getSuccessor(0) == BB || BI->getSuccessor(1) == BB);
|
|
auto *ConditionalConstant = (BI->getSuccessor(0) == BB) ?
|
|
ConstantInt::getTrue(BB->getContext()) :
|
|
ConstantInt::getFalse(BB->getContext());
|
|
AvailableValues.insert(CondInst, ConditionalConstant);
|
|
DEBUG(dbgs() << "EarlyCSE CVP: Add conditional value for '"
|
|
<< CondInst->getName() << "' as " << *ConditionalConstant
|
|
<< " in " << BB->getName() << "\n");
|
|
// Replace all dominated uses with the known value
|
|
replaceDominatedUsesWith(CondInst, ConditionalConstant, DT,
|
|
BasicBlockEdge(Pred, BB));
|
|
}
|
|
|
|
/// LastStore - Keep track of the last non-volatile store that we saw... for
|
|
/// as long as there in no instruction that reads memory. If we see a store
|
|
/// to the same location, we delete the dead store. This zaps trivial dead
|
|
/// stores which can occur in bitfield code among other things.
|
|
Instruction *LastStore = nullptr;
|
|
|
|
bool Changed = false;
|
|
const DataLayout &DL = BB->getModule()->getDataLayout();
|
|
|
|
// See if any instructions in the block can be eliminated. If so, do it. If
|
|
// not, add them to AvailableValues.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
|
|
Instruction *Inst = I++;
|
|
|
|
// Dead instructions should just be removed.
|
|
if (isInstructionTriviallyDead(Inst, &TLI)) {
|
|
DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++NumSimplify;
|
|
continue;
|
|
}
|
|
|
|
// Skip assume intrinsics, they don't really have side effects (although
|
|
// they're marked as such to ensure preservation of control dependencies),
|
|
// and this pass will not disturb any of the assumption's control
|
|
// dependencies.
|
|
if (match(Inst, m_Intrinsic<Intrinsic::assume>())) {
|
|
DEBUG(dbgs() << "EarlyCSE skipping assumption: " << *Inst << '\n');
|
|
continue;
|
|
}
|
|
|
|
// If the instruction can be simplified (e.g. X+0 = X) then replace it with
|
|
// its simpler value.
|
|
if (Value *V = SimplifyInstruction(Inst, DL, &TLI, &DT, &AC)) {
|
|
DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
|
|
Inst->replaceAllUsesWith(V);
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++NumSimplify;
|
|
continue;
|
|
}
|
|
|
|
// If this is a simple instruction that we can value number, process it.
|
|
if (SimpleValue::canHandle(Inst)) {
|
|
// See if the instruction has an available value. If so, use it.
|
|
if (Value *V = AvailableValues.lookup(Inst)) {
|
|
DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
|
|
Inst->replaceAllUsesWith(V);
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++NumCSE;
|
|
continue;
|
|
}
|
|
|
|
// Otherwise, just remember that this value is available.
|
|
AvailableValues.insert(Inst, Inst);
|
|
continue;
|
|
}
|
|
|
|
ParseMemoryInst MemInst(Inst, TTI);
|
|
// If this is a non-volatile load, process it.
|
|
if (MemInst.isValid() && MemInst.isLoad()) {
|
|
// Ignore volatile loads.
|
|
if (MemInst.isVolatile()) {
|
|
LastStore = nullptr;
|
|
// Don't CSE across synchronization boundaries.
|
|
if (Inst->mayWriteToMemory())
|
|
++CurrentGeneration;
|
|
continue;
|
|
}
|
|
|
|
// If we have an available version of this load, and if it is the right
|
|
// generation, replace this instruction.
|
|
std::pair<Value *, unsigned> InVal =
|
|
AvailableLoads.lookup(MemInst.getPtr());
|
|
if (InVal.first != nullptr && InVal.second == CurrentGeneration) {
|
|
Value *Op = getOrCreateResult(InVal.first, Inst->getType());
|
|
if (Op != nullptr) {
|
|
DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst
|
|
<< " to: " << *InVal.first << '\n');
|
|
if (!Inst->use_empty())
|
|
Inst->replaceAllUsesWith(Op);
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++NumCSELoad;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Otherwise, remember that we have this instruction.
|
|
AvailableLoads.insert(MemInst.getPtr(), std::pair<Value *, unsigned>(
|
|
Inst, CurrentGeneration));
|
|
LastStore = nullptr;
|
|
continue;
|
|
}
|
|
|
|
// If this instruction may read from memory, forget LastStore.
|
|
// Load/store intrinsics will indicate both a read and a write to
|
|
// memory. The target may override this (e.g. so that a store intrinsic
|
|
// does not read from memory, and thus will be treated the same as a
|
|
// regular store for commoning purposes).
|
|
if (Inst->mayReadFromMemory() &&
|
|
!(MemInst.isValid() && !MemInst.mayReadFromMemory()))
|
|
LastStore = nullptr;
|
|
|
|
// If this is a read-only call, process it.
|
|
if (CallValue::canHandle(Inst)) {
|
|
// If we have an available version of this call, and if it is the right
|
|
// generation, replace this instruction.
|
|
std::pair<Value *, unsigned> InVal = AvailableCalls.lookup(Inst);
|
|
if (InVal.first != nullptr && InVal.second == CurrentGeneration) {
|
|
DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst
|
|
<< " to: " << *InVal.first << '\n');
|
|
if (!Inst->use_empty())
|
|
Inst->replaceAllUsesWith(InVal.first);
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++NumCSECall;
|
|
continue;
|
|
}
|
|
|
|
// Otherwise, remember that we have this instruction.
|
|
AvailableCalls.insert(
|
|
Inst, std::pair<Value *, unsigned>(Inst, CurrentGeneration));
|
|
continue;
|
|
}
|
|
|
|
// Okay, this isn't something we can CSE at all. Check to see if it is
|
|
// something that could modify memory. If so, our available memory values
|
|
// cannot be used so bump the generation count.
|
|
if (Inst->mayWriteToMemory()) {
|
|
++CurrentGeneration;
|
|
|
|
if (MemInst.isValid() && MemInst.isStore()) {
|
|
// We do a trivial form of DSE if there are two stores to the same
|
|
// location with no intervening loads. Delete the earlier store.
|
|
if (LastStore) {
|
|
ParseMemoryInst LastStoreMemInst(LastStore, TTI);
|
|
if (LastStoreMemInst.isMatchingMemLoc(MemInst)) {
|
|
DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore
|
|
<< " due to: " << *Inst << '\n');
|
|
LastStore->eraseFromParent();
|
|
Changed = true;
|
|
++NumDSE;
|
|
LastStore = nullptr;
|
|
}
|
|
// fallthrough - we can exploit information about this store
|
|
}
|
|
|
|
// Okay, we just invalidated anything we knew about loaded values. Try
|
|
// to salvage *something* by remembering that the stored value is a live
|
|
// version of the pointer. It is safe to forward from volatile stores
|
|
// to non-volatile loads, so we don't have to check for volatility of
|
|
// the store.
|
|
AvailableLoads.insert(MemInst.getPtr(), std::pair<Value *, unsigned>(
|
|
Inst, CurrentGeneration));
|
|
|
|
// Remember that this was the last store we saw for DSE.
|
|
if (!MemInst.isVolatile())
|
|
LastStore = Inst;
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool EarlyCSE::run() {
|
|
// Note, deque is being used here because there is significant performance
|
|
// gains over vector when the container becomes very large due to the
|
|
// specific access patterns. For more information see the mailing list
|
|
// discussion on this:
|
|
// http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120116/135228.html
|
|
std::deque<StackNode *> nodesToProcess;
|
|
|
|
bool Changed = false;
|
|
|
|
// Process the root node.
|
|
nodesToProcess.push_back(new StackNode(
|
|
AvailableValues, AvailableLoads, AvailableCalls, CurrentGeneration,
|
|
DT.getRootNode(), DT.getRootNode()->begin(), DT.getRootNode()->end()));
|
|
|
|
// Save the current generation.
|
|
unsigned LiveOutGeneration = CurrentGeneration;
|
|
|
|
// Process the stack.
|
|
while (!nodesToProcess.empty()) {
|
|
// Grab the first item off the stack. Set the current generation, remove
|
|
// the node from the stack, and process it.
|
|
StackNode *NodeToProcess = nodesToProcess.back();
|
|
|
|
// Initialize class members.
|
|
CurrentGeneration = NodeToProcess->currentGeneration();
|
|
|
|
// Check if the node needs to be processed.
|
|
if (!NodeToProcess->isProcessed()) {
|
|
// Process the node.
|
|
Changed |= processNode(NodeToProcess->node());
|
|
NodeToProcess->childGeneration(CurrentGeneration);
|
|
NodeToProcess->process();
|
|
} else if (NodeToProcess->childIter() != NodeToProcess->end()) {
|
|
// Push the next child onto the stack.
|
|
DomTreeNode *child = NodeToProcess->nextChild();
|
|
nodesToProcess.push_back(
|
|
new StackNode(AvailableValues, AvailableLoads, AvailableCalls,
|
|
NodeToProcess->childGeneration(), child, child->begin(),
|
|
child->end()));
|
|
} else {
|
|
// It has been processed, and there are no more children to process,
|
|
// so delete it and pop it off the stack.
|
|
delete NodeToProcess;
|
|
nodesToProcess.pop_back();
|
|
}
|
|
} // while (!nodes...)
|
|
|
|
// Reset the current generation.
|
|
CurrentGeneration = LiveOutGeneration;
|
|
|
|
return Changed;
|
|
}
|
|
|
|
PreservedAnalyses EarlyCSEPass::run(Function &F,
|
|
AnalysisManager<Function> *AM) {
|
|
auto &TLI = AM->getResult<TargetLibraryAnalysis>(F);
|
|
auto &TTI = AM->getResult<TargetIRAnalysis>(F);
|
|
auto &DT = AM->getResult<DominatorTreeAnalysis>(F);
|
|
auto &AC = AM->getResult<AssumptionAnalysis>(F);
|
|
|
|
EarlyCSE CSE(F, TLI, TTI, DT, AC);
|
|
|
|
if (!CSE.run())
|
|
return PreservedAnalyses::all();
|
|
|
|
// CSE preserves the dominator tree because it doesn't mutate the CFG.
|
|
// FIXME: Bundle this with other CFG-preservation.
|
|
PreservedAnalyses PA;
|
|
PA.preserve<DominatorTreeAnalysis>();
|
|
return PA;
|
|
}
|
|
|
|
namespace {
|
|
/// \brief A simple and fast domtree-based CSE pass.
|
|
///
|
|
/// This pass does a simple depth-first walk over the dominator tree,
|
|
/// eliminating trivially redundant instructions and using instsimplify to
|
|
/// canonicalize things as it goes. It is intended to be fast and catch obvious
|
|
/// cases so that instcombine and other passes are more effective. It is
|
|
/// expected that a later pass of GVN will catch the interesting/hard cases.
|
|
class EarlyCSELegacyPass : public FunctionPass {
|
|
public:
|
|
static char ID;
|
|
|
|
EarlyCSELegacyPass() : FunctionPass(ID) {
|
|
initializeEarlyCSELegacyPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool runOnFunction(Function &F) override {
|
|
if (skipOptnoneFunction(F))
|
|
return false;
|
|
|
|
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
|
|
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
|
|
|
|
EarlyCSE CSE(F, TLI, TTI, DT, AC);
|
|
|
|
return CSE.run();
|
|
}
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addRequired<DominatorTreeWrapperPass>();
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
AU.addRequired<TargetTransformInfoWrapperPass>();
|
|
AU.setPreservesCFG();
|
|
}
|
|
};
|
|
}
|
|
|
|
char EarlyCSELegacyPass::ID = 0;
|
|
|
|
FunctionPass *llvm::createEarlyCSEPass() { return new EarlyCSELegacyPass(); }
|
|
|
|
INITIALIZE_PASS_BEGIN(EarlyCSELegacyPass, "early-cse", "Early CSE", false,
|
|
false)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_PASS_END(EarlyCSELegacyPass, "early-cse", "Early CSE", false, false)
|