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