[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

1 files changed, 15 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;
 }