[llvm-commits] [llvm] r142066 - /llvm/trunk/lib/Transforms/Scalar/GVN.cpp

[Duncan Sands]

Author: baldrick
Date: Sat Oct 15 06:13:42 2011
New Revision: 142066

URL: http://llvm.org/viewvc/llvm-project?rev=142066&view=rev
Log:
Don't replace all dominated uses if there is only one use, since that
use can't be dominated, saving one domtree lookup.

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

Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=142066&r1=142065&r2=142066&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Sat Oct 15 06:13:42 2011
@@ -1935,10 +1935,15 @@
   // to 'LHS' then ensure it will be turned into 'RHS'.
   addToLeaderTable(VN.lookup_or_add(LHS), RHS, Root);
 
-  // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope.
-  unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
-  bool Changed = NumReplacements > 0;
-  NumGVNEqProp += NumReplacements;
+  // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope.  As
+  // LHS always has at least one use that is not dominated by Root, this will
+  // never do anything if LHS has only one use.
+  bool Changed = false;
+  if (!LHS->hasOneUse()) {
+    unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
+    Changed |= NumReplacements > 0;
+    NumGVNEqProp += NumReplacements;
+  }
 
   // Now try to deduce additional equalities from this one.  For example, if the
   // known equality was "(A != B)" == "false" then it follows that A and B are