[llvm] cf15515 - [AggressiveInstCombine] Add support for ICmp instr that feeds a select intsr's condition operand.
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 12 05:04:07 PST 2020
Revert this please, i don't think this was reviewed, and tests are missing?
On Wed, Feb 12, 2020 at 4:01 PM Ayman Musa via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Ayman Musa
> Date: 2020-02-12T15:01:27+02:00
> New Revision: cf155150f992270c88e586ffc61973d2552b72e8
>
> URL: https://github.com/llvm/llvm-project/commit/cf155150f992270c88e586ffc61973d2552b72e8
> DIFF: https://github.com/llvm/llvm-project/commit/cf155150f992270c88e586ffc61973d2552b72e8.diff
>
> LOG: [AggressiveInstCombine] Add support for ICmp instr that feeds a select intsr's condition operand.
>
> Added:
>
>
> Modified:
> llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
>
> Removed:
>
>
>
> ################################################################################
> diff --git a/llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp b/llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
> index 0cfc6ef47d4b..3581a24851de 100644
> --- a/llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
> +++ b/llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
> @@ -36,6 +36,24 @@ using namespace llvm;
>
> #define DEBUG_TYPE "aggressive-instcombine"
>
> +// This function returns true if Value V is a constant or if it's a type
> +// extension node.
> +static bool isConstOrExt(Value *V) {
> + if (isa<Constant>(V))
> + return true;
> +
> + if (Instruction *I = dyn_cast<Instruction>(V)) {
> + switch(I->getOpcode()) {
> + case Instruction::ZExt:
> + case Instruction::SExt:
> + return true;
> + default:
> + return false;
> + }
> + }
> + return false;
> +}
> +
> /// Given an instruction and a container, it fills all the relevant operands of
> /// that instruction, with respect to the Trunc expression dag optimizaton.
> static void getRelevantOperands(Instruction *I, SmallVectorImpl<Value *> &Ops) {
> @@ -53,12 +71,20 @@ static void getRelevantOperands(Instruction *I, SmallVectorImpl<Value *> &Ops) {
> case Instruction::And:
> case Instruction::Or:
> case Instruction::Xor:
> + case Instruction::ICmp:
> Ops.push_back(I->getOperand(0));
> Ops.push_back(I->getOperand(1));
> break;
> case Instruction::Select:
> + Value *Op0 = I->getOperand(0);
> Ops.push_back(I->getOperand(1));
> Ops.push_back(I->getOperand(2));
> + // In case the condition is a compare instruction, that both of its operands
> + // are a type extension/truncate or a constant, that can be shrinked without
> + // loosing information in the compare instruction, add them as well.
> + if (CmpInst *C = dyn_cast<CmpInst>(Op0))
> + if (isConstOrExt(C->getOperand(0)) && isConstOrExt(C->getOperand(1)))
> + Ops.push_back(Op0);
> break;
> default:
> llvm_unreachable("Unreachable!");
> @@ -119,7 +145,8 @@ bool TruncInstCombine::buildTruncExpressionDag() {
> case Instruction::And:
> case Instruction::Or:
> case Instruction::Xor:
> - case Instruction::Select: {
> + case Instruction::Select:
> + case Instruction::ICmp: {
> SmallVector<Value *, 2> Operands;
> getRelevantOperands(I, Operands);
> for (Value *Operand : Operands)
> @@ -139,6 +166,21 @@ bool TruncInstCombine::buildTruncExpressionDag() {
> return true;
> }
>
> +// Get the minimum number of bits needed for the given constant.
> +static unsigned getConstMinBitWidth(bool IsSigned, ConstantInt *C) {
> + // If the const value is signed and negative, count the leading ones.
> + if (IsSigned) {
> + int64_t Val = C->getSExtValue();
> + uint64_t UVal = (uint64_t)Val;
> + if (Val < 0)
> + return sizeof(UVal)*8 - countLeadingOnes(UVal) + 1;
> + }
> + // Otherwise, count leading zeroes.
> + uint64_t Val = C->getZExtValue();
> + auto MinBits = sizeof(Val)*8 - countLeadingZeros(Val);
> + return IsSigned ? MinBits + 1 : MinBits;
> +}
> +
> unsigned TruncInstCombine::getMinBitWidth() {
> SmallVector<Value *, 8> Worklist;
> SmallVector<Instruction *, 8> Stack;
> @@ -180,6 +222,13 @@ unsigned TruncInstCombine::getMinBitWidth() {
> if (auto *IOp = dyn_cast<Instruction>(Operand))
> Info.MinBitWidth =
> std::max(Info.MinBitWidth, InstInfoMap[IOp].MinBitWidth);
> + else if (auto *C = dyn_cast<ConstantInt>(Operand)) {
> + // In case of Cmp instruction, make sure the constant can be truncated
> + // without losing information.
> + if (CmpInst *Cmp = dyn_cast<CmpInst>(I))
> + Info.MinBitWidth = std::max(
> + Info.MinBitWidth, getConstMinBitWidth(Cmp->isSigned(), C));
> + }
> continue;
> }
>
> @@ -193,14 +242,27 @@ unsigned TruncInstCombine::getMinBitWidth() {
>
> for (auto *Operand : Operands)
> if (auto *IOp = dyn_cast<Instruction>(Operand)) {
> - // If we already calculated the minimum bit-width for this valid
> - // bit-width, or for a smaller valid bit-width, then just keep the
> - // answer we already calculated.
> - unsigned IOpBitwidth = InstInfoMap.lookup(IOp).ValidBitWidth;
> - if (IOpBitwidth >= ValidBitWidth)
> - continue;
> - InstInfoMap[IOp].ValidBitWidth = ValidBitWidth;
> - Worklist.push_back(IOp);
> + if (isa<CmpInst>(I)) {
> + // Cmp instructions kind of resets the valid bits analysis for its
> + // operands, as it does not continue with the same calculation chain
> + // but rather creates a new chain of its own.
> + switch (IOp->getOpcode()) {
> + case Instruction::SExt:
> + case Instruction::ZExt:
> + InstInfoMap[IOp].ValidBitWidth =
> + cast<CastInst>(IOp)->getSrcTy()->getScalarSizeInBits();
> + break;
> + }
> + } else {
> + // If we already calculated the minimum bit-width for this valid
> + // bit-width, or for a smaller valid bit-width, then just keep the
> + // answer we already calculated.
> + unsigned IOpBitwidth = InstInfoMap.lookup(IOp).ValidBitWidth;
> + if (IOpBitwidth >= ValidBitWidth)
> + continue;
> + InstInfoMap[IOp].ValidBitWidth = ValidBitWidth;
> + Worklist.push_back(IOp);
> + }
> }
> }
> unsigned MinBitWidth = InstInfoMap.lookup(cast<Instruction>(Src)).MinBitWidth;
> @@ -363,6 +425,13 @@ void TruncInstCombine::ReduceExpressionDag(Type *SclTy) {
> Res = Builder.CreateSelect(Op0, LHS, RHS);
> break;
> }
> + case Instruction::ICmp: {
> + auto ICmp = cast<ICmpInst>(I);
> + Value *LHS = getReducedOperand(ICmp->getOperand(0), SclTy);
> + Value *RHS = getReducedOperand(ICmp->getOperand(1), SclTy);
> + Res = Builder.CreateICmp(ICmp->getPredicate(), LHS, RHS);
> + break;
> + }
> default:
> llvm_unreachable("Unhandled instruction");
> }
>
>
>
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