[llvm-commits] [llvm] r42582 - /llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

[Dale Johannesen]

Author: johannes
Date: Wed Oct  3 12:45:27 2007
New Revision: 42582

URL: http://llvm.org/viewvc/llvm-project?rev=42582&view=rev
Log:
Tone down an overzealous optimization.


Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: 
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=42582&r1=42581&r2=42582&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Wed Oct  3 
12:45:27 2007
@@ -7354,8 +7354,17 @@
   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 @@
 
     } 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);


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