forked from OSchip/llvm-project
653 lines
24 KiB
C++
653 lines
24 KiB
C++
//===- MergeICmps.cpp - Optimize chains of integer comparisons ------------===//
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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 turns chains of integer comparisons into memcmp (the memcmp is
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// later typically inlined as a chain of efficient hardware comparisons). This
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// typically benefits c++ member or nonmember operator==().
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//
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// The basic idea is to replace a larger chain of integer comparisons loaded
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// from contiguous memory locations into a smaller chain of such integer
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// comparisons. Benefits are double:
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// - There are less jumps, and therefore less opportunities for mispredictions
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// and I-cache misses.
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// - Code size is smaller, both because jumps are removed and because the
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// encoding of a 2*n byte compare is smaller than that of two n-byte
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// compares.
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//===----------------------------------------------------------------------===//
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#include <algorithm>
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#include <numeric>
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#include <utility>
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#include <vector>
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#include "llvm/ADT/APSInt.h"
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#include "llvm/Analysis/Loads.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/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/BuildLibCalls.h"
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using namespace llvm;
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namespace {
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#define DEBUG_TYPE "mergeicmps"
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// A BCE atom.
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struct BCEAtom {
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BCEAtom() : GEP(nullptr), LoadI(nullptr), Offset() {}
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const Value *Base() const { return GEP ? GEP->getPointerOperand() : nullptr; }
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bool operator<(const BCEAtom &O) const {
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assert(Base() && "invalid atom");
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assert(O.Base() && "invalid atom");
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// Just ordering by (Base(), Offset) is sufficient. However because this
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// means that the ordering will depend on the addresses of the base
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// values, which are not reproducible from run to run. To guarantee
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// stability, we use the names of the values if they exist; we sort by:
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// (Base.getName(), Base(), Offset).
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const int NameCmp = Base()->getName().compare(O.Base()->getName());
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if (NameCmp == 0) {
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if (Base() == O.Base()) {
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return Offset.slt(O.Offset);
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}
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return Base() < O.Base();
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}
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return NameCmp < 0;
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}
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GetElementPtrInst *GEP;
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LoadInst *LoadI;
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APInt Offset;
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};
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// If this value is a load from a constant offset w.r.t. a base address, and
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// there are no othe rusers of the load or address, returns the base address and
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// the offset.
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BCEAtom visitICmpLoadOperand(Value *const Val) {
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BCEAtom Result;
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if (auto *const LoadI = dyn_cast<LoadInst>(Val)) {
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DEBUG(dbgs() << "load\n");
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if (LoadI->isUsedOutsideOfBlock(LoadI->getParent())) {
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DEBUG(dbgs() << "used outside of block\n");
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return {};
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}
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if (LoadI->isVolatile()) {
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DEBUG(dbgs() << "volatile\n");
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return {};
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}
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Value *const Addr = LoadI->getOperand(0);
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if (auto *const GEP = dyn_cast<GetElementPtrInst>(Addr)) {
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DEBUG(dbgs() << "GEP\n");
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if (LoadI->isUsedOutsideOfBlock(LoadI->getParent())) {
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DEBUG(dbgs() << "used outside of block\n");
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return {};
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}
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const auto &DL = GEP->getModule()->getDataLayout();
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if (!isDereferenceablePointer(GEP, DL)) {
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DEBUG(dbgs() << "not dereferenceable\n");
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// We need to make sure that we can do comparison in any order, so we
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// require memory to be unconditionnally dereferencable.
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return {};
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}
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Result.Offset = APInt(DL.getPointerTypeSizeInBits(GEP->getType()), 0);
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if (GEP->accumulateConstantOffset(DL, Result.Offset)) {
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Result.GEP = GEP;
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Result.LoadI = LoadI;
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}
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}
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}
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return Result;
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}
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// A basic block with a comparison between two BCE atoms.
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// Note: the terminology is misleading: the comparison is symmetric, so there
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// is no real {l/r}hs. What we want though is to have the same base on the
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// left (resp. right), so that we can detect consecutive loads. To ensure this
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// we put the smallest atom on the left.
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class BCECmpBlock {
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public:
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BCECmpBlock() {}
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BCECmpBlock(BCEAtom L, BCEAtom R, int SizeBits)
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: Lhs_(L), Rhs_(R), SizeBits_(SizeBits) {
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if (Rhs_ < Lhs_) std::swap(Rhs_, Lhs_);
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}
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bool IsValid() const {
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return Lhs_.Base() != nullptr && Rhs_.Base() != nullptr;
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}
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// Assert the the block is consistent: If valid, it should also have
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// non-null members besides Lhs_ and Rhs_.
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void AssertConsistent() const {
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if (IsValid()) {
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assert(BB);
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assert(CmpI);
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assert(BranchI);
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}
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}
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const BCEAtom &Lhs() const { return Lhs_; }
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const BCEAtom &Rhs() const { return Rhs_; }
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int SizeBits() const { return SizeBits_; }
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// Returns true if the block does other works besides comparison.
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bool doesOtherWork() const;
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// The basic block where this comparison happens.
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BasicBlock *BB = nullptr;
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// The ICMP for this comparison.
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ICmpInst *CmpI = nullptr;
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// The terminating branch.
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BranchInst *BranchI = nullptr;
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private:
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BCEAtom Lhs_;
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BCEAtom Rhs_;
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int SizeBits_ = 0;
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};
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bool BCECmpBlock::doesOtherWork() const {
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AssertConsistent();
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// TODO(courbet): Can we allow some other things ? This is very conservative.
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// We might be able to get away with anything does does not have any side
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// effects outside of the basic block.
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// Note: The GEPs and/or loads are not necessarily in the same block.
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for (const Instruction &Inst : *BB) {
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if (const auto *const GEP = dyn_cast<GetElementPtrInst>(&Inst)) {
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if (!(Lhs_.GEP == GEP || Rhs_.GEP == GEP)) return true;
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} else if (const auto *const L = dyn_cast<LoadInst>(&Inst)) {
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if (!(Lhs_.LoadI == L || Rhs_.LoadI == L)) return true;
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} else if (const auto *const C = dyn_cast<ICmpInst>(&Inst)) {
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if (C != CmpI) return true;
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} else if (const auto *const Br = dyn_cast<BranchInst>(&Inst)) {
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if (Br != BranchI) return true;
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} else {
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return true;
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}
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}
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return false;
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}
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// Visit the given comparison. If this is a comparison between two valid
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// BCE atoms, returns the comparison.
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BCECmpBlock visitICmp(const ICmpInst *const CmpI,
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const ICmpInst::Predicate ExpectedPredicate) {
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if (CmpI->getPredicate() == ExpectedPredicate) {
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DEBUG(dbgs() << "cmp "
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<< (ExpectedPredicate == ICmpInst::ICMP_EQ ? "eq" : "ne")
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<< "\n");
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auto Lhs = visitICmpLoadOperand(CmpI->getOperand(0));
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if (!Lhs.Base()) return {};
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auto Rhs = visitICmpLoadOperand(CmpI->getOperand(1));
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if (!Rhs.Base()) return {};
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return BCECmpBlock(std::move(Lhs), std::move(Rhs),
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CmpI->getOperand(0)->getType()->getScalarSizeInBits());
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}
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return {};
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}
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// Visit the given comparison block. If this is a comparison between two valid
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// BCE atoms, returns the comparison.
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BCECmpBlock visitCmpBlock(Value *const Val, BasicBlock *const Block,
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const BasicBlock *const PhiBlock) {
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if (Block->empty()) return {};
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auto *const BranchI = dyn_cast<BranchInst>(Block->getTerminator());
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if (!BranchI) return {};
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DEBUG(dbgs() << "branch\n");
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if (BranchI->isUnconditional()) {
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// In this case, we expect an incoming value which is the result of the
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// comparison. This is the last link in the chain of comparisons (note
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// that this does not mean that this is the last incoming value, blocks
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// can be reordered).
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auto *const CmpI = dyn_cast<ICmpInst>(Val);
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if (!CmpI) return {};
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DEBUG(dbgs() << "icmp\n");
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auto Result = visitICmp(CmpI, ICmpInst::ICMP_EQ);
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Result.CmpI = CmpI;
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Result.BranchI = BranchI;
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return Result;
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} else {
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// In this case, we expect a constant incoming value (the comparison is
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// chained).
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const auto *const Const = dyn_cast<ConstantInt>(Val);
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DEBUG(dbgs() << "const\n");
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if (!Const->isZero()) return {};
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DEBUG(dbgs() << "false\n");
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auto *const CmpI = dyn_cast<ICmpInst>(BranchI->getCondition());
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if (!CmpI) return {};
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DEBUG(dbgs() << "icmp\n");
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assert(BranchI->getNumSuccessors() == 2 && "expecting a cond branch");
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BasicBlock *const FalseBlock = BranchI->getSuccessor(1);
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auto Result = visitICmp(
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CmpI, FalseBlock == PhiBlock ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE);
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Result.CmpI = CmpI;
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Result.BranchI = BranchI;
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return Result;
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}
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return {};
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}
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// A chain of comparisons.
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class BCECmpChain {
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public:
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BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi);
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int size() const { return Comparisons_.size(); }
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#ifdef MERGEICMPS_DOT_ON
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void dump() const;
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#endif // MERGEICMPS_DOT_ON
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bool simplify(const TargetLibraryInfo *const TLI);
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private:
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static bool IsContiguous(const BCECmpBlock &First,
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const BCECmpBlock &Second) {
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return First.Lhs().Base() == Second.Lhs().Base() &&
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First.Rhs().Base() == Second.Rhs().Base() &&
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First.Lhs().Offset + First.SizeBits() / 8 == Second.Lhs().Offset &&
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First.Rhs().Offset + First.SizeBits() / 8 == Second.Rhs().Offset;
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}
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// Merges the given comparison blocks into one memcmp block and update
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// branches. Comparisons are assumed to be continguous. If NextBBInChain is
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// null, the merged block will link to the phi block.
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static void mergeComparisons(ArrayRef<BCECmpBlock> Comparisons,
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BasicBlock *const NextBBInChain, PHINode &Phi,
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const TargetLibraryInfo *const TLI);
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PHINode &Phi_;
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std::vector<BCECmpBlock> Comparisons_;
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// The original entry block (before sorting);
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BasicBlock *EntryBlock_;
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};
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BCECmpChain::BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi)
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: Phi_(Phi) {
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// Now look inside blocks to check for BCE comparisons.
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std::vector<BCECmpBlock> Comparisons;
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for (BasicBlock *Block : Blocks) {
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BCECmpBlock Comparison = visitCmpBlock(Phi.getIncomingValueForBlock(Block),
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Block, Phi.getParent());
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Comparison.BB = Block;
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if (!Comparison.IsValid()) {
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DEBUG(dbgs() << "skip: not a valid BCECmpBlock\n");
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return;
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}
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if (Comparison.doesOtherWork()) {
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DEBUG(dbgs() << "block does extra work besides compare\n");
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if (Comparisons.empty()) { // First block.
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// TODO(courbet): The first block can do other things, and we should
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// split them apart in a separate block before the comparison chain.
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// Right now we just discard it and make the chain shorter.
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DEBUG(dbgs()
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<< "ignoring first block that does extra work besides compare\n");
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continue;
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}
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// TODO(courbet): Right now we abort the whole chain. We could be
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// merging only the blocks that don't do other work and resume the
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// chain from there. For example:
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// if (a[0] == b[0]) { // bb1
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// if (a[1] == b[1]) { // bb2
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// some_value = 3; //bb3
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// if (a[2] == b[2]) { //bb3
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// do a ton of stuff //bb4
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// }
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// }
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// }
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//
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// This is:
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//
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// bb1 --eq--> bb2 --eq--> bb3* -eq--> bb4 --+
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// \ \ \ \
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// ne ne ne \
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// \ \ \ v
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// +------------+-----------+----------> bb_phi
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//
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// We can only merge the first two comparisons, because bb3* does
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// "other work" (setting some_value to 3).
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// We could still merge bb1 and bb2 though.
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return;
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}
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DEBUG(dbgs() << "*Found cmp of " << Comparison.SizeBits()
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<< " bits between " << Comparison.Lhs().Base() << " + "
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<< Comparison.Lhs().Offset << " and "
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<< Comparison.Rhs().Base() << " + " << Comparison.Rhs().Offset
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<< "\n");
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DEBUG(dbgs() << "\n");
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Comparisons.push_back(Comparison);
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}
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EntryBlock_ = Comparisons[0].BB;
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Comparisons_ = std::move(Comparisons);
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#ifdef MERGEICMPS_DOT_ON
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errs() << "BEFORE REORDERING:\n\n";
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dump();
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#endif // MERGEICMPS_DOT_ON
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// Reorder blocks by LHS. We can do that without changing the
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// semantics because we are only accessing dereferencable memory.
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std::sort(Comparisons_.begin(), Comparisons_.end(),
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[](const BCECmpBlock &a, const BCECmpBlock &b) {
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return a.Lhs() < b.Lhs();
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});
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#ifdef MERGEICMPS_DOT_ON
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errs() << "AFTER REORDERING:\n\n";
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dump();
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#endif // MERGEICMPS_DOT_ON
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}
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#ifdef MERGEICMPS_DOT_ON
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void BCECmpChain::dump() const {
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errs() << "digraph dag {\n";
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errs() << " graph [bgcolor=transparent];\n";
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errs() << " node [color=black,style=filled,fillcolor=lightyellow];\n";
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errs() << " edge [color=black];\n";
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for (size_t I = 0; I < Comparisons_.size(); ++I) {
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const auto &Comparison = Comparisons_[I];
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errs() << " \"" << I << "\" [label=\"%"
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<< Comparison.Lhs().Base()->getName() << " + "
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<< Comparison.Lhs().Offset << " == %"
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<< Comparison.Rhs().Base()->getName() << " + "
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<< Comparison.Rhs().Offset << " (" << (Comparison.SizeBits() / 8)
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<< " bytes)\"];\n";
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const Value *const Val = Phi_.getIncomingValueForBlock(Comparison.BB);
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if (I > 0) errs() << " \"" << (I - 1) << "\" -> \"" << I << "\";\n";
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errs() << " \"" << I << "\" -> \"Phi\" [label=\"" << *Val << "\"];\n";
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}
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errs() << " \"Phi\" [label=\"Phi\"];\n";
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errs() << "}\n\n";
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}
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#endif // MERGEICMPS_DOT_ON
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bool BCECmpChain::simplify(const TargetLibraryInfo *const TLI) {
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// First pass to check if there is at least one merge. If not, we don't do
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// anything and we keep analysis passes intact.
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{
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bool AtLeastOneMerged = false;
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for (size_t I = 1; I < Comparisons_.size(); ++I) {
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if (IsContiguous(Comparisons_[I - 1], Comparisons_[I])) {
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AtLeastOneMerged = true;
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break;
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}
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}
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if (!AtLeastOneMerged) return false;
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}
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// Remove phi references to comparison blocks, they will be rebuilt as we
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// merge the blocks.
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for (const auto &Comparison : Comparisons_) {
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Phi_.removeIncomingValue(Comparison.BB, false);
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}
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// Point the predecessors of the chain to the first comparison block (which is
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// the new entry point).
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if (EntryBlock_ != Comparisons_[0].BB)
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EntryBlock_->replaceAllUsesWith(Comparisons_[0].BB);
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// Effectively merge blocks.
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int NumMerged = 1;
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for (size_t I = 1; I < Comparisons_.size(); ++I) {
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if (IsContiguous(Comparisons_[I - 1], Comparisons_[I])) {
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++NumMerged;
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} else {
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// Merge all previous comparisons and start a new merge block.
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mergeComparisons(
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makeArrayRef(Comparisons_).slice(I - NumMerged, NumMerged),
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Comparisons_[I].BB, Phi_, TLI);
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NumMerged = 1;
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}
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}
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mergeComparisons(makeArrayRef(Comparisons_)
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.slice(Comparisons_.size() - NumMerged, NumMerged),
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nullptr, Phi_, TLI);
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return true;
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}
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void BCECmpChain::mergeComparisons(ArrayRef<BCECmpBlock> Comparisons,
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BasicBlock *const NextBBInChain,
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PHINode &Phi,
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const TargetLibraryInfo *const TLI) {
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assert(!Comparisons.empty());
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const auto &FirstComparison = *Comparisons.begin();
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BasicBlock *const BB = FirstComparison.BB;
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LLVMContext &Context = BB->getContext();
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if (Comparisons.size() >= 2) {
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DEBUG(dbgs() << "Merging " << Comparisons.size() << " comparisons\n");
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const auto TotalSize =
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std::accumulate(Comparisons.begin(), Comparisons.end(), 0,
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[](int Size, const BCECmpBlock &C) {
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return Size + C.SizeBits();
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}) /
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8;
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// Incoming edges do not need to be updated, and both GEPs are already
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// computing the right address, we just need to:
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// - replace the two loads and the icmp with the memcmp
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// - update the branch
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// - update the incoming values in the phi.
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FirstComparison.BranchI->eraseFromParent();
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FirstComparison.CmpI->eraseFromParent();
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FirstComparison.Lhs().LoadI->eraseFromParent();
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FirstComparison.Rhs().LoadI->eraseFromParent();
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IRBuilder<> Builder(BB);
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const auto &DL = Phi.getModule()->getDataLayout();
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Value *const MemCmpCall = emitMemCmp(
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FirstComparison.Lhs().GEP, FirstComparison.Rhs().GEP, ConstantInt::get(DL.getIntPtrType(Context), TotalSize),
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Builder, DL, TLI);
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Value *const MemCmpIsZero = Builder.CreateICmpEQ(
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MemCmpCall, ConstantInt::get(Type::getInt32Ty(Context), 0));
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// Add a branch to the next basic block in the chain.
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if (NextBBInChain) {
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Builder.CreateCondBr(MemCmpIsZero, NextBBInChain, Phi.getParent());
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Phi.addIncoming(ConstantInt::getFalse(Context), BB);
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} else {
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Builder.CreateBr(Phi.getParent());
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Phi.addIncoming(MemCmpIsZero, BB);
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}
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// Delete merged blocks.
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for (size_t I = 1; I < Comparisons.size(); ++I) {
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BasicBlock *CBB = Comparisons[I].BB;
|
|
CBB->replaceAllUsesWith(BB);
|
|
CBB->eraseFromParent();
|
|
}
|
|
} else {
|
|
assert(Comparisons.size() == 1);
|
|
// There are no blocks to merge, but we still need to update the branches.
|
|
DEBUG(dbgs() << "Only one comparison, updating branches\n");
|
|
if (NextBBInChain) {
|
|
if (FirstComparison.BranchI->isConditional()) {
|
|
DEBUG(dbgs() << "conditional -> conditional\n");
|
|
// Just update the "true" target, the "false" target should already be
|
|
// the phi block.
|
|
assert(FirstComparison.BranchI->getSuccessor(1) == Phi.getParent());
|
|
FirstComparison.BranchI->setSuccessor(0, NextBBInChain);
|
|
Phi.addIncoming(ConstantInt::getFalse(Context), BB);
|
|
} else {
|
|
DEBUG(dbgs() << "unconditional -> conditional\n");
|
|
// Replace the unconditional branch by a conditional one.
|
|
FirstComparison.BranchI->eraseFromParent();
|
|
IRBuilder<> Builder(BB);
|
|
Builder.CreateCondBr(FirstComparison.CmpI, NextBBInChain,
|
|
Phi.getParent());
|
|
Phi.addIncoming(FirstComparison.CmpI, BB);
|
|
}
|
|
} else {
|
|
if (FirstComparison.BranchI->isConditional()) {
|
|
DEBUG(dbgs() << "conditional -> unconditional\n");
|
|
// Replace the conditional branch by an unconditional one.
|
|
FirstComparison.BranchI->eraseFromParent();
|
|
IRBuilder<> Builder(BB);
|
|
Builder.CreateBr(Phi.getParent());
|
|
Phi.addIncoming(FirstComparison.CmpI, BB);
|
|
} else {
|
|
DEBUG(dbgs() << "unconditional -> unconditional\n");
|
|
Phi.addIncoming(FirstComparison.CmpI, BB);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
std::vector<BasicBlock *> getOrderedBlocks(PHINode &Phi,
|
|
BasicBlock *const LastBlock,
|
|
int NumBlocks) {
|
|
// Walk up from the last block to find other blocks.
|
|
std::vector<BasicBlock *> Blocks(NumBlocks);
|
|
BasicBlock *CurBlock = LastBlock;
|
|
for (int BlockIndex = NumBlocks - 1; BlockIndex > 0; --BlockIndex) {
|
|
if (CurBlock->hasAddressTaken()) {
|
|
// Somebody is jumping to the block through an address, all bets are
|
|
// off.
|
|
DEBUG(dbgs() << "skip: block " << BlockIndex
|
|
<< " has its address taken\n");
|
|
return {};
|
|
}
|
|
Blocks[BlockIndex] = CurBlock;
|
|
auto *SinglePredecessor = CurBlock->getSinglePredecessor();
|
|
if (!SinglePredecessor) {
|
|
// The block has two or more predecessors.
|
|
DEBUG(dbgs() << "skip: block " << BlockIndex
|
|
<< " has two or more predecessors\n");
|
|
return {};
|
|
}
|
|
if (Phi.getBasicBlockIndex(SinglePredecessor) < 0) {
|
|
// The block does not link back to the phi.
|
|
DEBUG(dbgs() << "skip: block " << BlockIndex
|
|
<< " does not link back to the phi\n");
|
|
return {};
|
|
}
|
|
CurBlock = SinglePredecessor;
|
|
}
|
|
Blocks[0] = CurBlock;
|
|
return Blocks;
|
|
}
|
|
|
|
bool processPhi(PHINode &Phi, const TargetLibraryInfo *const TLI) {
|
|
DEBUG(dbgs() << "processPhi()\n");
|
|
if (Phi.getNumIncomingValues() <= 1) {
|
|
DEBUG(dbgs() << "skip: only one incoming value in phi\n");
|
|
return false;
|
|
}
|
|
// We are looking for something that has the following structure:
|
|
// bb1 --eq--> bb2 --eq--> bb3 --eq--> bb4 --+
|
|
// \ \ \ \
|
|
// ne ne ne \
|
|
// \ \ \ v
|
|
// +------------+-----------+----------> bb_phi
|
|
//
|
|
// - The last basic block (bb4 here) must branch unconditionally to bb_phi.
|
|
// It's the only block that contributes a non-constant value to the Phi.
|
|
// - All other blocks (b1, b2, b3) must have exactly two successors, one of
|
|
// them being the the phi block.
|
|
// - All intermediate blocks (bb2, bb3) must have only one predecessor.
|
|
// - Blocks cannot do other work besides the comparison, see doesOtherWork()
|
|
|
|
// The blocks are not necessarily ordered in the phi, so we start from the
|
|
// last block and reconstruct the order.
|
|
BasicBlock *LastBlock = nullptr;
|
|
for (unsigned I = 0; I < Phi.getNumIncomingValues(); ++I) {
|
|
if (isa<ConstantInt>(Phi.getIncomingValue(I))) continue;
|
|
if (LastBlock) {
|
|
// There are several non-constant values.
|
|
DEBUG(dbgs() << "skip: several non-constant values\n");
|
|
return false;
|
|
}
|
|
LastBlock = Phi.getIncomingBlock(I);
|
|
}
|
|
if (!LastBlock) {
|
|
// There is no non-constant block.
|
|
DEBUG(dbgs() << "skip: no non-constant block\n");
|
|
return false;
|
|
}
|
|
if (LastBlock->getSingleSuccessor() != Phi.getParent()) {
|
|
DEBUG(dbgs() << "skip: last block non-phi successor\n");
|
|
return false;
|
|
}
|
|
|
|
const auto Blocks =
|
|
getOrderedBlocks(Phi, LastBlock, Phi.getNumIncomingValues());
|
|
if (Blocks.empty()) return false;
|
|
BCECmpChain CmpChain(Blocks, Phi);
|
|
|
|
if (CmpChain.size() < 2) {
|
|
DEBUG(dbgs() << "skip: only one compare block\n");
|
|
return false;
|
|
}
|
|
|
|
return CmpChain.simplify(TLI);
|
|
}
|
|
|
|
class MergeICmps : public FunctionPass {
|
|
public:
|
|
static char ID;
|
|
|
|
MergeICmps() : FunctionPass(ID) {
|
|
initializeMergeICmpsPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool runOnFunction(Function &F) override {
|
|
if (skipFunction(F)) return false;
|
|
const auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
const auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
|
|
auto PA = runImpl(F, &TLI, &TTI);
|
|
return !PA.areAllPreserved();
|
|
}
|
|
|
|
private:
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
AU.addRequired<TargetTransformInfoWrapperPass>();
|
|
}
|
|
|
|
PreservedAnalyses runImpl(Function &F, const TargetLibraryInfo *TLI,
|
|
const TargetTransformInfo *TTI);
|
|
};
|
|
|
|
PreservedAnalyses MergeICmps::runImpl(Function &F, const TargetLibraryInfo *TLI,
|
|
const TargetTransformInfo *TTI) {
|
|
DEBUG(dbgs() << "MergeICmpsPass: " << F.getName() << "\n");
|
|
|
|
// We only try merging comparisons if the target wants to expand memcmp later.
|
|
// The rationale is to avoid turning small chains into memcmp calls.
|
|
if (!TTI->enableMemCmpExpansion(true)) return PreservedAnalyses::all();
|
|
|
|
bool MadeChange = false;
|
|
|
|
for (auto BBIt = ++F.begin(); BBIt != F.end(); ++BBIt) {
|
|
// A Phi operation is always first in a basic block.
|
|
if (auto *const Phi = dyn_cast<PHINode>(&*BBIt->begin()))
|
|
MadeChange |= processPhi(*Phi, TLI);
|
|
}
|
|
|
|
if (MadeChange) return PreservedAnalyses::none();
|
|
return PreservedAnalyses::all();
|
|
}
|
|
|
|
} // namespace
|
|
|
|
char MergeICmps::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(MergeICmps, "mergeicmps",
|
|
"Merge contiguous icmps into a memcmp", false, false)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
|
|
INITIALIZE_PASS_END(MergeICmps, "mergeicmps",
|
|
"Merge contiguous icmps into a memcmp", false, false)
|
|
|
|
Pass *llvm::createMergeICmpsPass() { return new MergeICmps(); }
|