[llvm] 0f56bbc - [InstCombine] reduce FP-casted and bitcasted signbit check
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sat Mar 28 06:47:36 PDT 2020
Alive2 confirms the -0.0 problem:
http://volta.cs.utah.edu:8080/z/f39Rw-
NaN inputs could also be wrong. We could do better given fast-math-flags,
but I'm avoiding that without strong motivation...because FMF on fcmp is a
mess ( https://bugs.llvm.org/show_bug.cgi?id=38086 ).
(It would be interesting to have Alive2 command-line options to disallow
-0.0 or NaN values similar to the -disable-undef-input option.)
We do have this transform for fcmp already:
// fcmp (fpext X), C -> fcmp X, (fptrunc C) if fptrunc is lossless
And I think that's as far as we can take it - there is no fptrunc sibling
for that because truncation loses bits:
http://volta.cs.utah.edu:8080/z/zTheyA
On Sat, Mar 28, 2020 at 4:38 AM Roman Lebedev <lebedev.ri at gmail.com> wrote:
> 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) {
> >> >
> >> >
> >> >
> >> > _______________________________________________
> >> > llvm-commits mailing list
> >> > llvm-commits at lists.llvm.org
> >> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
> >> _______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
> >
> > --
> > ~Craig
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200328/da1237ef/attachment-0001.html>
More information about the llvm-commits
mailing list