InstSimplify: Fold fdiv nnan ninf x, 0 -> poison

[kpn]

Looks like IEEE 754-2019 section 7.3 says this should result in Infinity, but the ninf flag excludes Infinity, so poison seems correct.

LGTM

[spatel]

llvm/test/Transforms/InstSimplify/fdiv.ll

64

This Alive2 link is showing folding to infinity rather than poison. Please adjust. Also, add the amended link to the patch summary/commit message?

[arsenm]

llvm/test/Transforms/InstSimplify/fdiv.ll

64

This link is in a pre-commit to add new tests, I'll fix it there

[spatel]

llvm/test/Transforms/InstSimplify/fdiv.ll

64

That works.

[arsenm]

7dd27a75a261f57c6d038eb5faa421c49b12f1d5

llvm/lib/Analysis/InstructionSimplify.cpp

if (FMF.allowReassoc() && match(Op0, m_c_FMul(m_Value(X), m_Specific(Op1))))
       return X;
 
     // -X /  X -> -1.0 and
     //  X / -X -> -1.0 are legal when NaNs are ignored.
     // We can ignore signed zeros because +-0.0/+-0.0 is NaN and ignored.
     if (match(Op0, m_FNegNSZ(m_Specific(Op1))) ||
         match(Op1, m_FNegNSZ(m_Specific(Op0))))
       return ConstantFP::get(Op0->getType(), -1.0);
+
+    // nnan ninf X / 0.0 -> poison
+    if (FMF.noInfs() && match(Op1, m_AnyZeroFP()))
+      return PoisonValue::get(Op1->getType());
   }
 
   return nullptr;
 }
 
 Value *llvm::simplifyFDivInst(Value *Op0, Value *Op1, FastMathFlags FMF,
                               const SimplifyQuery &Q,
                               fp::ExceptionBehavior ExBehavior,

llvm/test/Transforms/InstSimplify/fdiv.ll

 ; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %fdiv = fdiv <2 x float> undef, <float 1.000000e+00, float 1.000000e+00>
   %fcmp = fcmp ole <2 x float> %fdiv, zeroinitializer
   ret <2 x i1> %fcmp
 }
 
 
 ; https://alive2.llvm.org/ce/z/ryZBn6
 define float @fdiv_nnan_ninf_by_zero_f32(float %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_zero_f32(
-; CHECK-NEXT:    [[FDIV:%.*]] = fdiv nnan ninf float [[X:%.*]], 0.000000e+00
-; CHECK-NEXT:    ret float [[FDIV]]
+; CHECK-NEXT:    ret float poison
 ;
   %fdiv = fdiv nnan ninf float %x, 0.0
   ret float %fdiv
 }
 
 define float @fdiv_nnan_ninf_by_negzero_f32(float %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_negzero_f32(
-; CHECK-NEXT:    [[FDIV:%.*]] = fdiv nnan ninf float [[X:%.*]], -0.000000e+00
-; CHECK-NEXT:    ret float [[FDIV]]
+; CHECK-NEXT:    ret float poison
 ;
   %fdiv = fdiv nnan ninf float %x, -0.0
   ret float %fdiv
 }
 
 define float @fdiv_nnan_ninf_by_undef_f32(float %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_undef_f32(
 ; CHECK-NEXT:    ret float poison
 ;
   %fdiv = fdiv nnan ninf float %x, undef
   ret float %fdiv
 }
 
 define float @fdiv_nnan_ninf_by_poison_f32(float %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_poison_f32(
 ; CHECK-NEXT:    ret float poison
 ;
   %fdiv = fdiv nnan ninf float %x, poison
   ret float %fdiv
 }
 
 define <2 x float> @fdiv_nnan_ninf_by_zero_v2f32(<2 x float> %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_zero_v2f32(
-; CHECK-NEXT:    [[FDIV:%.*]] = fdiv nnan ninf <2 x float> [[X:%.*]], zeroinitializer
-; CHECK-NEXT:    ret <2 x float> [[FDIV]]
+; CHECK-NEXT:    ret <2 x float> poison
 ;
   %fdiv = fdiv nnan ninf <2 x float> %x, zeroinitializer
   ret <2 x float> %fdiv
 }
 
 define <2 x float> @fdiv_nnan_ninf_by_undef_v2f32(<2 x float> %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_undef_v2f32(
 ; CHECK-NEXT:    ret <2 x float> poison
 ;
   %fdiv = fdiv nnan ninf <2 x float> %x, undef
   ret <2 x float> %fdiv
 }
 
 define <2 x float> @fdiv_nnan_ninf_by_zero_undef_v2f32(<2 x float> %x) {
 ; CHECK-LABEL: @fdiv_nnan_ninf_by_zero_undef_v2f32(
-; CHECK-NEXT:    [[FDIV:%.*]] = fdiv nnan ninf <2 x float> [[X:%.*]], <float 0.000000e+00, float undef>
-; CHECK-NEXT:    ret <2 x float> [[FDIV]]
+; CHECK-NEXT:    ret <2 x float> poison
 ;
   %fdiv = fdiv nnan ninf <2 x float> %x, <float 0.0, float undef>
   ret <2 x float> %fdiv
 }
 
 ; https://alive2.llvm.org/ce/z/ryZBn6
 define float @fdiv_nnan_nsz_ninf_by_zero_f32(float %x) {
 ; CHECK-LABEL: @fdiv_nnan_nsz_ninf_by_zero_f32(