[llvm] acabad9 - [InstCombine] try to canonicalize icmp with trunc op into mask and cmp
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 26 14:47:19 PDT 2021
Should this simply use `decomposeBitTestICmp()`?
Roman
On Wed, Oct 27, 2021 at 12:45 AM Sanjay Patel via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Sanjay Patel
> Date: 2021-10-26T17:43:28-04:00
> New Revision: acabad9ff6bf13e00305d9d8621ee8eafc1f8b08
>
> URL: https://github.com/llvm/llvm-project/commit/acabad9ff6bf13e00305d9d8621ee8eafc1f8b08
> DIFF: https://github.com/llvm/llvm-project/commit/acabad9ff6bf13e00305d9d8621ee8eafc1f8b08.diff
>
> LOG: [InstCombine] try to canonicalize icmp with trunc op into mask and cmp
>
> The motivating test is based on:
> https://llvm.org/PR52260
>
> We have better analysis for X == 0, so try harder to form that.
>
> Added:
>
>
> Modified:
> llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> llvm/test/Transforms/InstCombine/icmp-trunc.ll
> llvm/test/Transforms/InstCombine/signed-truncation-check.ll
>
> Removed:
>
>
>
> ################################################################################
> diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> index 54d751e30ee3..a2db1bc83e76 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> @@ -4589,6 +4589,31 @@ Instruction *InstCombinerImpl::foldICmpEquality(ICmpInst &I) {
> return nullptr;
> }
>
> +static Instruction *foldICmpWithTrunc(ICmpInst &ICmp,
> + InstCombiner::BuilderTy &Builder) {
> + const ICmpInst::Predicate Pred = ICmp.getPredicate();
> + Value *Op0 = ICmp.getOperand(0), *Op1 = ICmp.getOperand(1);
> +
> + // Try to canonicalize trunc + compare-to-constant into a mask + cmp.
> + // The trunc masks high bits while the compare may effectively mask low bits.
> + Value *X;
> + const APInt *C;
> + if (match(Op0, m_OneUse(m_Trunc(m_Value(X)))) && match(Op1, m_Power2(C))) {
> + if (Pred == ICmpInst::ICMP_ULT) {
> + // (trunc X) u< Pow2C --> (X & MaskC) == 0
> + unsigned SrcBits = X->getType()->getScalarSizeInBits();
> + unsigned DstBits = Op0->getType()->getScalarSizeInBits();
> + APInt MaskC = APInt::getOneBitSet(SrcBits, DstBits) - C->zext(SrcBits);
> + Value *And = Builder.CreateAnd(X, MaskC);
> + Constant *Zero = ConstantInt::getNullValue(X->getType());
> + return new ICmpInst(ICmpInst::ICMP_EQ, And, Zero);
> + }
> + // TODO: Handle ugt.
> + }
> +
> + return nullptr;
> +}
> +
> static Instruction *foldICmpWithZextOrSext(ICmpInst &ICmp,
> InstCombiner::BuilderTy &Builder) {
> assert(isa<CastInst>(ICmp.getOperand(0)) && "Expected cast for operand 0");
> @@ -4732,6 +4757,9 @@ Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
> return new ICmpInst(ICmp.getPredicate(), Op0Src, NewOp1);
> }
>
> + if (Instruction *R = foldICmpWithTrunc(ICmp, Builder))
> + return R;
> +
> return foldICmpWithZextOrSext(ICmp, Builder);
> }
>
>
> diff --git a/llvm/test/Transforms/InstCombine/icmp-trunc.ll b/llvm/test/Transforms/InstCombine/icmp-trunc.ll
> index 7f961f2ccfaf..39ca767a6d2a 100644
> --- a/llvm/test/Transforms/InstCombine/icmp-trunc.ll
> +++ b/llvm/test/Transforms/InstCombine/icmp-trunc.ll
> @@ -5,8 +5,8 @@ declare void @use(i8)
>
> define i1 @ult_2(i32 %x) {
> ; CHECK-LABEL: @ult_2(
> -; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
> -; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[T]], 2
> +; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 254
> +; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 0
> ; CHECK-NEXT: ret i1 [[R]]
> ;
> %t = trunc i32 %x to i8
> @@ -16,8 +16,8 @@ define i1 @ult_2(i32 %x) {
>
> define <2 x i1> @ult_16_splat(<2 x i16> %x) {
> ; CHECK-LABEL: @ult_16_splat(
> -; CHECK-NEXT: [[T:%.*]] = trunc <2 x i16> [[X:%.*]] to <2 x i11>
> -; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i11> [[T]], <i11 16, i11 16>
> +; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i16> [[X:%.*]], <i16 2032, i16 2032>
> +; CHECK-NEXT: [[R:%.*]] = icmp eq <2 x i16> [[TMP1]], zeroinitializer
> ; CHECK-NEXT: ret <2 x i1> [[R]]
> ;
> %t = trunc <2 x i16> %x to <2 x i11>
> @@ -25,6 +25,8 @@ define <2 x i1> @ult_16_splat(<2 x i16> %x) {
> ret <2 x i1> %r
> }
>
> +; negative test - need power-of-2 constant
> +
> define i1 @ult_3(i32 %x) {
> ; CHECK-LABEL: @ult_3(
> ; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
> @@ -36,6 +38,8 @@ define i1 @ult_3(i32 %x) {
> ret i1 %r
> }
>
> +; negative test - no extra use allowed
> +
> define i1 @ult_2_use(i32 %x) {
> ; CHECK-LABEL: @ult_2_use(
> ; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
> @@ -53,12 +57,7 @@ define i1 @ult_2_use(i32 %x) {
>
> define i1 @PR52260(i32 %x) {
> ; CHECK-LABEL: @PR52260(
> -; CHECK-NEXT: [[IDXPROM:%.*]] = sext i32 [[X:%.*]] to i64
> -; CHECK-NEXT: [[IDX:%.*]] = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 [[IDXPROM]]
> -; CHECK-NEXT: [[T1:%.*]] = load i32, i32* [[IDX]], align 4
> -; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[T1]] to i8
> -; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ult i8 [[TMP1]], 2
> -; CHECK-NEXT: ret i1 [[TOBOOL]]
> +; CHECK-NEXT: ret i1 true
> ;
> %idxprom = sext i32 %x to i64
> %idx = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 %idxprom
> @@ -69,4 +68,3 @@ define i1 @PR52260(i32 %x) {
> %tobool = icmp eq i8 %conv2, 0
> ret i1 %tobool
> }
> -
>
> diff --git a/llvm/test/Transforms/InstCombine/signed-truncation-check.ll b/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
> index 105e77284b93..6681d5021472 100644
> --- a/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
> +++ b/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
> @@ -397,8 +397,8 @@ define i1 @positive_trunc_signbit_logical(i32 %arg) {
>
> define i1 @positive_trunc_base(i32 %arg) {
> ; CHECK-LABEL: @positive_trunc_base(
> -; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
> -; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
> +; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
> +; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
> ; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
> ;
> %t1 = trunc i32 %arg to i16
> @@ -411,8 +411,8 @@ define i1 @positive_trunc_base(i32 %arg) {
>
> define i1 @positive_trunc_base_logical(i32 %arg) {
> ; CHECK-LABEL: @positive_trunc_base_logical(
> -; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
> -; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
> +; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
> +; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
> ; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
> ;
> %t1 = trunc i32 %arg to i16
>
>
>
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