[llvm] 0f56bbc - [InstCombine] reduce FP-casted and bitcasted signbit check
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Sat Mar 28 01:38:05 PDT 2020
Ah yes, indeed. Sorry for the noise.
On Sat, Mar 28, 2020 at 10:31 AM Craig Topper <craig.topper at gmail.com> wrote:
>
> Fp compare wouldn’t handle negative 0 correctly would it?
>
> On Fri, Mar 27, 2020 at 11:27 PM Roman Lebedev via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> On Sat, Mar 28, 2020 at 12:34 AM Sanjay Patel via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>> >
>> >
>> > Author: Sanjay Patel
>> > Date: 2020-03-27T17:33:59-04:00
>> > New Revision: 0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0
>> >
>> > URL: https://github.com/llvm/llvm-project/commit/0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0
>> > DIFF: https://github.com/llvm/llvm-project/commit/0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0.diff
>> >
>> > LOG: [InstCombine] reduce FP-casted and bitcasted signbit check
>> >
>> > PR45305:
>> > https://bugs.llvm.org/show_bug.cgi?id=45305
>> >
>> > Alive2 proofs:
>> > http://volta.cs.utah.edu:8080/z/bVyrko
>> > http://volta.cs.utah.edu:8080/z/Vxpz9q
>> >
>> > Added:
>> >
>> >
>> > Modified:
>> > llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > llvm/test/Transforms/InstCombine/icmp.ll
>> >
>> > Removed:
>> >
>> >
>> >
>> > ################################################################################
>> > diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > index 63bf3462faac..62b99e8b8b5b 100644
>> > --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > @@ -2760,6 +2760,30 @@ static Instruction *foldICmpBitCast(ICmpInst &Cmp,
>> > if (match(BCSrcOp, m_UIToFP(m_Value(X))))
>> > if (Cmp.isEquality() && match(Op1, m_Zero()))
>> > return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType()));
>> > +
>> > + // If this is a sign-bit test of a bitcast of a casted FP value, eliminate
>> > + // the FP cast because the FP cast does not change the sign-bit.
>> > + const APInt *C;
>> > + bool TrueIfSigned;
>> > + if (match(Op1, m_APInt(C)) && Bitcast->hasOneUse() &&
>> > + isSignBitCheck(Pred, *C, TrueIfSigned)) {
>> > + if (match(BCSrcOp, m_FPExt(m_Value(X))) ||
>> > + match(BCSrcOp, m_FPTrunc(m_Value(X)))) {
>> > + // (bitcast (fpext/fptrunc X)) to iX) < 0 --> (bitcast X to iY) < 0
>> > + // (bitcast (fpext/fptrunc X)) to iX) > -1 --> (bitcast X to iY) > -1
>> > + Type *XType = X->getType();
>> > + Type *NewType = Builder.getIntNTy(XType->getScalarSizeInBits());
>> > + if (XType->isVectorTy())
>> > + NewType = VectorType::get(NewType, XType->getVectorNumElements());
>> > + Value *NewBitcast = Builder.CreateBitCast(X, NewType);
>> > + if (TrueIfSigned)
>> > + return new ICmpInst(ICmpInst::ICMP_SLT, NewBitcast,
>> > + ConstantInt::getNullValue(NewType));
>> > + else
>> > + return new ICmpInst(ICmpInst::ICMP_SGT, NewBitcast,
>> > + ConstantInt::getAllOnesValue(NewType));
>> > + }
>> > + }
>> > }
>> >
>> > // Test to see if the operands of the icmp are casted versions of other
>> >
>> > diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
>> > index b2c6213399b0..41bf661b092e 100644
>> > --- a/llvm/test/Transforms/InstCombine/icmp.ll
>> > +++ b/llvm/test/Transforms/InstCombine/icmp.ll
>> > @@ -3609,9 +3609,8 @@ define <2 x i32> @Op1Negated_Vec(<2 x i32> %x) {
>> >
>> > define i1 @signbit_bitcast_fpext(float %x) {
>> > ; CHECK-LABEL: @signbit_bitcast_fpext(
>> > -; CHECK-NEXT: [[F:%.*]] = fpext float [[X:%.*]] to double
>> > -; CHECK-NEXT: [[B:%.*]] = bitcast double [[F]] to i64
>> > -; CHECK-NEXT: [[R:%.*]] = icmp slt i64 [[B]], 0
>> > +; CHECK-NEXT: [[TMP1:%.*]] = bitcast float [[X:%.*]] to i32
>> > +; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[TMP1]], 0
>> > ; CHECK-NEXT: ret i1 [[R]]
>> Not that i disagree with the transform, but why do we want to keep bitcast
>> instead of producing fp comparison?
>>
>> We then would want to split this fold:
>> (bitcast (fpext/fptrunc X)) to iX) < 0 --> (fpext/fptrunc X) < 0
>> (fpext/fptrunc X) < 0 --> X < 0
>>
>> > %f = fpext float %x to double
>> > @@ -3622,9 +3621,8 @@ define i1 @signbit_bitcast_fpext(float %x) {
>> >
>> > define <2 x i1> @signbit_bitcast_fpext_vec(<2 x half> %x) {
>> > ; CHECK-LABEL: @signbit_bitcast_fpext_vec(
>> > -; CHECK-NEXT: [[F:%.*]] = fpext <2 x half> [[X:%.*]] to <2 x float>
>> > -; CHECK-NEXT: [[B:%.*]] = bitcast <2 x float> [[F]] to <2 x i32>
>> > -; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i32> [[B]], zeroinitializer
>> > +; CHECK-NEXT: [[TMP1:%.*]] = bitcast <2 x half> [[X:%.*]] to <2 x i16>
>> > +; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i16> [[TMP1]], zeroinitializer
>> > ; CHECK-NEXT: ret <2 x i1> [[R]]
>> > ;
>> > %f = fpext <2 x half> %x to <2 x float>
>> > @@ -3635,9 +3633,8 @@ define <2 x i1> @signbit_bitcast_fpext_vec(<2 x half> %x) {
>> >
>> > define i1 @signbit_bitcast_fptrunc(float %x) {
>> > ; CHECK-LABEL: @signbit_bitcast_fptrunc(
>> > -; CHECK-NEXT: [[F:%.*]] = fptrunc float [[X:%.*]] to half
>> > -; CHECK-NEXT: [[B:%.*]] = bitcast half [[F]] to i16
>> > -; CHECK-NEXT: [[R:%.*]] = icmp sgt i16 [[B]], -1
>> > +; CHECK-NEXT: [[TMP1:%.*]] = bitcast float [[X:%.*]] to i32
>> > +; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[TMP1]], -1
>> > ; CHECK-NEXT: ret i1 [[R]]
>> > ;
>> > %f = fptrunc float %x to half
>> > @@ -3648,9 +3645,8 @@ define i1 @signbit_bitcast_fptrunc(float %x) {
>> >
>> > define <2 x i1> @signbit_bitcast_fptrunc_vec(<2 x double> %x) {
>> > ; CHECK-LABEL: @signbit_bitcast_fptrunc_vec(
>> > -; CHECK-NEXT: [[F:%.*]] = fptrunc <2 x double> [[X:%.*]] to <2 x half>
>> > -; CHECK-NEXT: [[B:%.*]] = bitcast <2 x half> [[F]] to <2 x i16>
>> > -; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i16> [[B]], <i16 -1, i16 -1>
>> > +; CHECK-NEXT: [[TMP1:%.*]] = bitcast <2 x double> [[X:%.*]] to <2 x i64>
>> > +; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i64> [[TMP1]], <i64 -1, i64 -1>
>> > ; CHECK-NEXT: ret <2 x i1> [[R]]
>> > ;
>> > %f = fptrunc <2 x double> %x to <2 x half>
>> > @@ -3672,6 +3668,19 @@ define i1 @signbit_bitcast_fpext_wrong_cmp(float %x) {
>> > ret i1 %r
>> > }
>> >
>> > +define <4 x i1> @signbit_bitcast_fpext_vec_wrong_bitcast(<2 x half> %x) {
>> > +; CHECK-LABEL: @signbit_bitcast_fpext_vec_wrong_bitcast(
>> > +; CHECK-NEXT: [[F:%.*]] = fpext <2 x half> [[X:%.*]] to <2 x float>
>> > +; CHECK-NEXT: [[B:%.*]] = bitcast <2 x float> [[F]] to <4 x i16>
>> > +; CHECK-NEXT: [[R:%.*]] = icmp sgt <4 x i16> [[B]], <i16 -1, i16 -1, i16 -1, i16 -1>
>> > +; CHECK-NEXT: ret <4 x i1> [[R]]
>> > +;
>> > + %f = fpext <2 x half> %x to <2 x float>
>> > + %b = bitcast <2 x float> %f to <4 x i16>
>> > + %r = icmp sgt <4 x i16> %b, <i16 -1, i16 -1, i16 -1, i16 -1>
>> > + ret <4 x i1> %r
>> > +}
>> > +
>> > declare void @use_i64(i64)
>> >
>> > define i1 @signbit_bitcast_fpext_extra_use(float %x, i64* %p) {
>> >
>> >
>> >
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>
> --
> ~Craig
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