From: Dale Johannesen <dalej@apple.com>
Date: Wed, 3 Oct 2007 17:45:27 +0000 (+0000)
Subject: Tone down an overzealous optimization.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=5a2174febf6a91c46833b24d2c47a7f5ea1d7ff1;p=oota-llvm.git

Tone down an overzealous optimization.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42582 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 3a7d1018c40..2311f1eb5a3 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -7354,8 +7354,17 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
       // Transform (X == Y) ? X : Y  -> Y
-      if (FCI->getPredicate() == FCmpInst::FCMP_OEQ)
+      if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
+        // This is not safe in general for floating point:  
+        // consider X== -0, Y== +0.
+        // It becomes safe if either operand is a nonzero constant.
+        ConstantFP *CFPt, *CFPf;
+        if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
+              !CFPt->getValueAPF().isZero()) ||
+            ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
+             !CFPf->getValueAPF().isZero()))
         return ReplaceInstUsesWith(SI, FalseVal);
+      }
       // Transform (X != Y) ? X : Y  -> X
       if (FCI->getPredicate() == FCmpInst::FCMP_ONE)
         return ReplaceInstUsesWith(SI, TrueVal);
@@ -7363,8 +7372,17 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 
     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
       // Transform (X == Y) ? Y : X  -> X
-      if (FCI->getPredicate() == FCmpInst::FCMP_OEQ)
-        return ReplaceInstUsesWith(SI, FalseVal);
+      if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
+        // This is not safe in general for floating point:  
+        // consider X== -0, Y== +0.
+        // It becomes safe if either operand is a nonzero constant.
+        ConstantFP *CFPt, *CFPf;
+        if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
+              !CFPt->getValueAPF().isZero()) ||
+            ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
+             !CFPf->getValueAPF().isZero()))
+          return ReplaceInstUsesWith(SI, FalseVal);
+      }
       // Transform (X != Y) ? Y : X  -> Y
       if (FCI->getPredicate() == FCmpInst::FCMP_ONE)
         return ReplaceInstUsesWith(SI, TrueVal);