[InstCombine] x /c fabs(x) -> copysign(1.0, x)

Summary:
x / fabs(x) -> copysign(1.0, x)
fabs(x) / x -> copysign(1.0, x)

Reviewers: spatel, foad, RKSimon, efriedma

Reviewed By: spatel

Subscribers: lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65898

llvm-svn: 368570

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 046944851d3..7f152aac52d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1234,6 +1234,17 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
     return &I;
   }
 
+  // X / fabs(X) -> copysign(1.0, X)
+  // fabs(X) / X -> copysign(1.0, X)
+  if (I.hasNoNaNs() && I.hasNoInfs() &&
+      (match(&I,
+             m_FDiv(m_Value(X), m_Intrinsic<Intrinsic::fabs>(m_Deferred(X)))) ||
+       match(&I, m_FDiv(m_Intrinsic<Intrinsic::fabs>(m_Value(X)),
+                        m_Deferred(X))))) {
+    Value *V = Builder.CreateBinaryIntrinsic(
+        Intrinsic::copysign, ConstantFP::get(I.getType(), 1.0), X, &I);
+    return replaceInstUsesWith(I, V);
+  }
   return nullptr;
 }