From: Owen Anderson <resistor@mac.com>
Date: Thu, 16 Jan 2014 20:36:42 +0000 (+0000)
Subject: Teach InstCombine that (fmul X, -1.0) can be simplified to (fneg X), which LLVM expre... 
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=a2a8bbb30f271843dd0678f563a62154919e09b4;p=oota-llvm.git

Teach InstCombine that (fmul X, -1.0) can be simplified to (fneg X), which LLVM expresses as (fsub -0.0, X).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199420 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a7595482eed..6c34b1bf566 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -426,6 +426,16 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
         return NV;
 
     ConstantFP *C = dyn_cast<ConstantFP>(Op1);
+
+    // (fmul X, -1.0) --> (fsub -0.0, X)
+    if (C && C->isExactlyValue(-1.0)) {
+      Instruction *RI = BinaryOperator::CreateFSub(
+        ConstantFP::getNegativeZero(C->getType()),
+        Op0);
+      RI->copyFastMathFlags(&I);
+      return RI;
+    }
+
     if (C && AllowReassociate && C->getValueAPF().isFiniteNonZero()) {
       // Let MDC denote an expression in one of these forms:
       // X * C, C/X, X/C, where C is a constant.
diff --git a/test/Transforms/InstCombine/fmul.ll b/test/Transforms/InstCombine/fmul.ll
index 402ee52e624..71b7138b644 100644
--- a/test/Transforms/InstCombine/fmul.ll
+++ b/test/Transforms/InstCombine/fmul.ll
@@ -93,3 +93,15 @@ for.body:                                         ; preds = %for.cond
 for.end:                                          ; preds = %for.cond
   ret void
 }
+
+; X * -1.0 => -0.0 - X
+define float @test9(float %x) {
+  %mul = fmul float %x, -1.0
+  ret float %mul
+
+; CHECK-LABEL: @test9(
+; CHECK-NOT: fmul
+; CHECK: fsub
+}
+
+