From 5ee5e0c4305fd6a1870bfc9d4fc82bf96f2d499e Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Thu, 16 Jan 2014 21:26:02 +0000
Subject: [PATCH] Fix two cases where we could lose fast math flags when
 optimizing FADD expressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199427 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineAddSub.cpp         | 14 +++++++++----
 test/Transforms/InstCombine/fast-math.ll      | 20 +++++++++++++++++++
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 534feb8fad2..d49153e4823 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1198,13 +1198,19 @@ Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
 
   // -A + B  -->  B - A
   // -A + -B  -->  -(A + B)
-  if (Value *LHSV = dyn_castFNegVal(LHS))
-    return BinaryOperator::CreateFSub(RHS, LHSV);
+  if (Value *LHSV = dyn_castFNegVal(LHS)) {
+    Instruction *RI = BinaryOperator::CreateFSub(RHS, LHSV);
+    RI->copyFastMathFlags(&I);
+    return RI;
+  }
 
   // A + -B  -->  A - B
   if (!isa<Constant>(RHS))
-    if (Value *V = dyn_castFNegVal(RHS))
-      return BinaryOperator::CreateFSub(LHS, V);
+    if (Value *V = dyn_castFNegVal(RHS)) {
+      Instruction *RI = BinaryOperator::CreateFSub(LHS, V);
+      RI->copyFastMathFlags(&I);
+      return RI;
+    }
 
   // Check for (fadd double (sitofp x), y), see if we can merge this into an
   // integer add followed by a promotion.
diff --git a/test/Transforms/InstCombine/fast-math.ll b/test/Transforms/InstCombine/fast-math.ll
index d8ba2a59ff5..0371488dfd8 100644
--- a/test/Transforms/InstCombine/fast-math.ll
+++ b/test/Transforms/InstCombine/fast-math.ll
@@ -140,6 +140,26 @@ define float @fold13(float %x) {
 ; CHECK: ret
 }
 
+; -x + y => y - x
+define float @fold14(float %x, float %y) {
+  %neg = fsub fast float -0.0, %x
+  %add = fadd fast float %neg, %y
+  ret float %add
+; CHECK: fold14
+; CHECK: fsub fast float %y, %x
+; CHECK: ret
+}
+
+; x + -y => x - y
+define float @fold15(float %x, float %y) {
+  %neg = fsub fast float -0.0, %y
+  %add = fadd fast float %x, %neg
+  ret float %add
+; CHECK: fold15
+; CHECK: fsub fast float %x, %y
+; CHECK: ret
+}
+
 ; =========================================================================
 ;
 ;   Testing-cases about fmul begin