commit cf9ba823240ec6d3682ba2ddeab5cdcf04092c77
author Mon P Wang <wangmp@apple.com> Sat Jan 31 06:07:45 2009 +0000
committer Mon P Wang <wangmp@apple.com> Sat Jan 31 06:07:45 2009 +0000
tree 01955ca4ac9d26f7b80c37f724ccf279d764065c
parent 3b585af0ecddfa8b09f0e2d329138094c689164f

If unsafe FP optimization is not set, don't allow -(A-B) => B-A because
when A==B, -0.0 != +0.0.

llvm-svn: 63474

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index bda9d93..f5287b0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2357,7 +2357,8 @@
       return Operand.getOperand(0);
     break;
   case ISD::FNEG:
-    if (OpOpcode == ISD::FSUB)   // -(X-Y) -> (Y-X)
+    // -(X-Y) -> (Y-X) is unsafe because when X==Y, -0.0 != +0.0
+    if (UnsafeFPMath && OpOpcode == ISD::FSUB)
       return getNode(ISD::FSUB, VT, Operand.getNode()->getOperand(1),
                      Operand.getNode()->getOperand(0));
     if (OpOpcode == ISD::FNEG)  // --X -> X