[llvm-commits] [llvm] r151524 - /llvm/trunk/lib/Transforms/Scalar/GVN.cpp

[Duncan Sands]

Author: baldrick
Date: Mon Feb 27 06:11:41 2012
New Revision: 151524

URL: http://llvm.org/viewvc/llvm-project?rev=151524&view=rev
Log:
Micro-optimization, no functionality change.

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=151524&r1=151523&r2=151524&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Mon Feb 27 06:11:41 2012
@@ -2041,13 +2041,18 @@
     // Since we don't have the instruction "A < B" immediately to hand, work out
     // the value number that it would have and use that to find an appropriate
     // instruction (if any).
-    unsigned Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
-    Value *NotCmp = findLeader(Root, Num);
-    if (NotCmp && isa<Instruction>(NotCmp)) {
-      unsigned NumReplacements =
-        replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
-      Changed |= NumReplacements > 0;
-      NumGVNEqProp += NumReplacements;
+    uint32_t NextNum = VN.getNextUnusedValueNumber();
+    uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
+    // If the number we were assigned was brand new then there is no point in
+    // looking for an instruction realizing it: there cannot be one!
+    if (Num < NextNum) {
+      Value *NotCmp = findLeader(Root, Num);
+      if (NotCmp && isa<Instruction>(NotCmp)) {
+        unsigned NumReplacements =
+          replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
+        Changed |= NumReplacements > 0;
+        NumGVNEqProp += NumReplacements;
+      }
     }
     // Ensure that any instruction in scope that gets the "A < B" value number
     // is replaced with false.