[llvm] 4069ccc - [InstCombine] fold icmp with sub and bool
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Sun May 22 09:11:09 PDT 2022
On Sun, May 22, 2022 at 5:54 PM Sanjay Patel via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
>
> Author: Sanjay Patel
> Date: 2022-05-22T11:51:07-04:00
> New Revision: 4069cccf3b4ff4afb743d3d371ead9e2d5491e3a
>
> URL:
> https://github.com/llvm/llvm-project/commit/4069cccf3b4ff4afb743d3d371ead9e2d5491e3a
> DIFF:
> https://github.com/llvm/llvm-project/commit/4069cccf3b4ff4afb743d3d371ead9e2d5491e3a.diff
>
> LOG: [InstCombine] fold icmp with sub and bool
>
> This is the specific pattern seen in #53432, but it can be extended
> in multiple ways:
> 1. The 'zext' could be an 'and'
> 2. The 'sub' could be some other binop with a similar ==0 property (udiv).
>
> There might be some way to generalize using knownbits, but that
> would require checking that the 'bool' value is created with
> some instruction that can be replaced with new icmp+logic.
>
> https://alive2.llvm.org/ce/z/-KCfpa
>
Are the multi-use cases here motivating? Otherwise, I would have found it
more intuitive to use a pattern like https://alive2.llvm.org/ce/z/XqbXm4
that is not specific to sub.
Nikita
> Added:
>
>
> Modified:
> llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> llvm/test/Transforms/InstCombine/icmp-range.ll
>
> Removed:
>
>
>
>
> ################################################################################
> diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> index 4f20a0699ec50..e2a6b6b1495b8 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> @@ -5631,6 +5631,29 @@ Instruction
> *InstCombinerImpl::foldICmpUsingKnownBits(ICmpInst &I) {
> return nullptr;
> }
>
> +/// If one operand of an icmp is effectively a bool (value range of
> {0,1}),
> +/// then try to reduce patterns based on that limit.
> +static Instruction *foldICmpUsingBoolRange(ICmpInst &I,
> + InstCombiner::BuilderTy
> &Builder) {
> + Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
> + const ICmpInst::Predicate Pred = I.getPredicate();
> +
> + Value *X, *Y, *Z;
> + if (Pred != ICmpInst::ICMP_ULT || !match(Op0, m_Sub(m_Value(X),
> m_Value(Y))))
> + return nullptr;
> +
> + unsigned ExtraUses = !Op0->hasOneUse() + !Op1->hasOneUse();
> +
> + // Sub must be 0 and bool must be true for "ULT":
> + // (sub X, Y) <u (zext i1 Z) --> (X == Y) && Z
> + if (match(Op1, m_ZExt(m_Value(Z))) && ExtraUses < 2) {
> + Value *EqXY = Builder.CreateICmpEQ(X, Y);
> + return BinaryOperator::CreateAnd(EqXY, Z);
> + }
> +
> + return nullptr;
> +}
> +
> llvm::Optional<std::pair<CmpInst::Predicate, Constant *>>
> InstCombiner::getFlippedStrictnessPredicateAndConstant(CmpInst::Predicate
> Pred,
> Constant *C) {
> @@ -6058,6 +6081,9 @@ Instruction
> *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
> if (Instruction *Res = foldICmpWithDominatingICmp(I))
> return Res;
>
> + if (Instruction *Res = foldICmpUsingBoolRange(I, Builder))
> + return Res;
> +
> if (Instruction *Res = foldICmpUsingKnownBits(I))
> return Res;
>
>
> diff --git a/llvm/test/Transforms/InstCombine/icmp-range.ll
> b/llvm/test/Transforms/InstCombine/icmp-range.ll
> index b67356675eba6..a29d4cd81b9d1 100644
> --- a/llvm/test/Transforms/InstCombine/icmp-range.ll
> +++ b/llvm/test/Transforms/InstCombine/icmp-range.ll
> @@ -173,9 +173,8 @@ define i1 @test_two_ranges3(i32* nocapture readonly
> %arg1, i32* nocapture readon
>
> define i1 @sub_ult_zext(i1 %b, i8 %x, i8 %y) {
> ; CHECK-LABEL: @sub_ult_zext(
> -; CHECK-NEXT: [[Z:%.*]] = zext i1 [[B:%.*]] to i8
> -; CHECK-NEXT: [[S:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[S]], [[Z]]
> +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
> +; CHECK-NEXT: [[R:%.*]] = and i1 [[TMP1]], [[B:%.*]]
> ; CHECK-NEXT: ret i1 [[R]]
> ;
> %z = zext i1 %b to i8
> @@ -188,8 +187,8 @@ define i1 @sub_ult_zext_use1(i1 %b, i8 %x, i8 %y) {
> ; CHECK-LABEL: @sub_ult_zext_use1(
> ; CHECK-NEXT: [[Z:%.*]] = zext i1 [[B:%.*]] to i8
> ; CHECK-NEXT: call void @use(i8 [[Z]])
> -; CHECK-NEXT: [[S:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[S]], [[Z]]
> +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
> +; CHECK-NEXT: [[R:%.*]] = and i1 [[TMP1]], [[B]]
> ; CHECK-NEXT: ret i1 [[R]]
> ;
> %z = zext i1 %b to i8
> @@ -201,10 +200,10 @@ define i1 @sub_ult_zext_use1(i1 %b, i8 %x, i8 %y) {
>
> define <2 x i1> @zext_ugt_sub_use2(<2 x i1> %b, <2 x i8> %x, <2 x i8> %y)
> {
> ; CHECK-LABEL: @zext_ugt_sub_use2(
> -; CHECK-NEXT: [[Z:%.*]] = zext <2 x i1> [[B:%.*]] to <2 x i8>
> ; CHECK-NEXT: [[S:%.*]] = sub <2 x i8> [[X:%.*]], [[Y:%.*]]
> ; CHECK-NEXT: call void @use_vec(<2 x i8> [[S]])
> -; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i8> [[S]], [[Z]]
> +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq <2 x i8> [[X]], [[Y]]
> +; CHECK-NEXT: [[R:%.*]] = and <2 x i1> [[TMP1]], [[B:%.*]]
> ; CHECK-NEXT: ret <2 x i1> [[R]]
> ;
> %z = zext <2 x i1> %b to <2 x i8>
> @@ -214,6 +213,8 @@ define <2 x i1> @zext_ugt_sub_use2(<2 x i1> %b, <2 x
> i8> %x, <2 x i8> %y) {
> ret <2 x i1> %r
> }
>
> +; negative test - too many extra uses
> +
> define i1 @sub_ult_zext_use3(i1 %b, i8 %x, i8 %y) {
> ; CHECK-LABEL: @sub_ult_zext_use3(
> ; CHECK-NEXT: [[Z:%.*]] = zext i1 [[B:%.*]] to i8
> @@ -231,6 +232,8 @@ define i1 @sub_ult_zext_use3(i1 %b, i8 %x, i8 %y) {
> ret i1 %r
> }
>
> +; negative test - wrong predicate
> +
> define i1 @sub_ule_zext(i1 %b, i8 %x, i8 %y) {
> ; CHECK-LABEL: @sub_ule_zext(
> ; CHECK-NEXT: [[Z:%.*]] = zext i1 [[B:%.*]] to i8
>
>
>
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