[llvm] 4069ccc - [InstCombine] fold icmp with sub and bool
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sun May 22 09:17:03 PDT 2022
Thanks! Yes, the pattern without sub is probably good enough, and I botched
that implementation (bots failing), so reverted.
On Sun, May 22, 2022 at 12:14 PM Nikita Popov <nikita.ppv at gmail.com> wrote:
> On Sun, May 22, 2022 at 6:11 PM Nikita Popov <nikita.ppv at gmail.com> wrote:
>
>> 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.
>>
>
> Also, isn't this missing a check that the zext is from i1 rather than some
> other type?
>
> 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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>>
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