[InstSimplify] Add self-fdiv identities for -ffinite-math-only.

When NaNs and Infs are ignored we can fold
 X /  X -> 1.0
-X /  X -> -1.0
 X / -X -> -1.0

llvm-svn: 239701

2 files changed, 92 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index ec56d888dc2..5e3b415a2a6 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1126,6 +1126,21 @@ 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 (Op0 == Op1)
+      return ConstantFP::get(Op0->getType(), 1.0);
+
+    // -X /  X -> -1.0 and
+    //  X / -X -> -1.0 iff NaNs and infinities 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) ||
+        (BinaryOperator::isFNeg(Op1, /*IgnoreZeroSign=*/true) &&
+         BinaryOperator::getFNegArgument(Op1) == Op0))
+      return ConstantFP::get(Op0->getType(), -1.0);
+  }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstSimplify/fast-math.ll b/llvm/test/Transforms/InstSimplify/fast-math.ll
index e7fb14d7e78..0336301c354 100644
--- a/llvm/test/Transforms/InstSimplify/fast-math.ll
+++ b/llvm/test/Transforms/InstSimplify/fast-math.ll
@@ -114,3 +114,80 @@ define double @fdiv_zero_by_x(double %X) {
   ret double %r
 ; CHECK: ret double 0
 }
+
+define float @fdiv_self(float %f)  {
+  %div = fdiv nnan ninf 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)  {
+  %div = fdiv float %f, %f
+  ret float %div
+; CHECK-LABEL: fdiv_self_invalid3
+; CHECK: %div = fdiv float %f, %f
+; CHECK-NEXT: ret float %div
+}
+
+define float @fdiv_neg(float %f) {
+  %neg = fsub fast float -0.000000e+00, %f
+  %div = fdiv nnan ninf float %neg, %f
+  ret float %div
+; CHECK-LABEL: fdiv_neg
+; 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
+  %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
+}
+
+define float @fdiv_neg_invalid3(float %f) {
+  %neg = fsub fast float -0.000000e+00, %f
+  %div = fdiv float %neg, %f
+  ret float %div
+; CHECK-LABEL: fdiv_neg_invalid3
+; 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) {
+  %neg = fsub float 0.000000e+00, %f
+  %div = fdiv nnan ninf float %f, %neg
+  ret float %div
+; CHECK-LABEL: fdiv_neg_swapped
+; CHECK: ret float -1.000000e+00
+}