[InstSimplify] Allow folding of fdiv X, X with just NaNs ignored

Any combination of +-inf/+-inf is NaN so it's already ignored with
nnan and we can skip checking for ninf. Also rephrase logic in comments
a bit.

llvm-svn: 239821

2 files changed, 27 insertions, 47 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 8f7a940aa95..12e406bb1a2 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1126,13 +1126,13 @@ static Value *SimplifyFDivInst(Value *Op0, Value *Op1, FastMathFlags FMF,
   if (FMF.noNaNs() && FMF.noSignedZeros() && match(Op0, m_AnyZero()))
     return Op0;
 
-  if (FMF.noNaNs() && FMF.noInfs()) {
-    // X / X -> 1.0 iff NaNs and infinities are ignored.
+  if (FMF.noNaNs()) {
+    // X / X -> 1.0 is legal when NaNs are ignored.
     if (Op0 == Op1)
       return ConstantFP::get(Op0->getType(), 1.0);
 
     // -X /  X -> -1.0 and
-    //  X / -X -> -1.0 iff NaNs and infinities are ignored.
+    //  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 ((BinaryOperator::isFNeg(Op0, /*IgnoreZeroSign=*/true) &&
          BinaryOperator::getFNegArgument(Op0) == Op1) ||
diff --git a/llvm/test/Transforms/InstSimplify/fast-math.ll b/llvm/test/Transforms/InstSimplify/fast-math.ll
index c9ae7ef0f09..90532fa5db8 100644
--- a/llvm/test/Transforms/InstSimplify/fast-math.ll
+++ b/llvm/test/Transforms/InstSimplify/fast-math.ll
@@ -115,79 +115,59 @@ define double @fdiv_zero_by_x(double %X) {
 ; CHECK: ret double 0
 }
 
-define float @fdiv_self(float %f)  {
-  %div = fdiv nnan ninf float %f, %f
+define float @fdiv_self(float %f) {
+  %div = fdiv nnan float %f, %f
   ret float %div
 ; CHECK-LABEL: fdiv_self
 ; CHECK: ret float 1.000000e+00
 }
 
-define float @fdiv_self_invalid1(float %f)  {
-  %div = fdiv ninf float %f, %f
-  ret float %div
-; CHECK-LABEL: fdiv_self_invalid1
-; CHECK: %div = fdiv ninf float %f, %f
-; CHECK-NEXT: ret float %div
-}
-
-define float @fdiv_self_invalid2(float %f)  {
-  %div = fdiv nnan float %f, %f
-  ret float %div
-; CHECK-LABEL: fdiv_self_invalid2
-; CHECK: %div = fdiv nnan float %f, %f
-; CHECK-NEXT: ret float %div
-}
-
-define float @fdiv_self_invalid3(float %f)  {
+define float @fdiv_self_invalid(float %f) {
   %div = fdiv float %f, %f
   ret float %div
-; CHECK-LABEL: fdiv_self_invalid3
+; CHECK-LABEL: fdiv_self_invalid
 ; CHECK: %div = fdiv float %f, %f
 ; CHECK-NEXT: ret float %div
 }
 
-define float @fdiv_neg(float %f) {
+define float @fdiv_neg1(float %f) {
   %neg = fsub fast float -0.000000e+00, %f
-  %div = fdiv nnan ninf float %neg, %f
+  %div = fdiv nnan float %neg, %f
   ret float %div
-; CHECK-LABEL: fdiv_neg
+; CHECK-LABEL: fdiv_neg1
 ; CHECK: ret float -1.000000e+00
 }
 
-define float @fdiv_neg_invalid1(float %f) {
-  %neg = fsub fast float -0.000000e+00, %f
-  %div = fdiv ninf float %neg, %f
-  ret float %div
-; CHECK-LABEL: fdiv_neg_invalid1
-; CHECK: %neg = fsub fast float -0.000000e+00, %f
-; CHECK-NEXT: %div = fdiv ninf float %neg, %f
-; CHECK-NEXT: ret float %div
-}
-
-define float @fdiv_neg_invalid2(float %f) {
-  %neg = fsub fast float -0.000000e+00, %f
+define float @fdiv_neg2(float %f) {
+  %neg = fsub fast float 0.000000e+00, %f
   %div = fdiv nnan float %neg, %f
   ret float %div
-; CHECK-LABEL: fdiv_neg_invalid2
-; CHECK: %neg = fsub fast float -0.000000e+00, %f
-; CHECK-NEXT: %div = fdiv nnan float %neg, %f
-; CHECK-NEXT: ret float %div
+; CHECK-LABEL: fdiv_neg2
+; CHECK: ret float -1.000000e+00
 }
 
-define float @fdiv_neg_invalid3(float %f) {
+define float @fdiv_neg_invalid(float %f) {
   %neg = fsub fast float -0.000000e+00, %f
   %div = fdiv float %neg, %f
   ret float %div
-; CHECK-LABEL: fdiv_neg_invalid3
+; CHECK-LABEL: fdiv_neg_invalid
 ; CHECK: %neg = fsub fast float -0.000000e+00, %f
 ; CHECK-NEXT: %div = fdiv float %neg, %f
 ; CHECK-NEXT: ret float %div
 }
 
-define float @fdiv_neg_swapped(float %f) {
+define float @fdiv_neg_swapped1(float %f) {
+  %neg = fsub float -0.000000e+00, %f
+  %div = fdiv nnan float %f, %neg
+  ret float %div
+; CHECK-LABEL: fdiv_neg_swapped1
+; CHECK: ret float -1.000000e+00
+}
+
+define float @fdiv_neg_swapped2(float %f) {
   %neg = fsub float 0.000000e+00, %f
-  %div = fdiv nnan ninf float %f, %neg
+  %div = fdiv nnan float %f, %neg
   ret float %div
-; CHECK-LABEL: fdiv_neg_swapped
+; CHECK-LABEL: fdiv_neg_swapped2
 ; CHECK: ret float -1.000000e+00
 }