[llvm-commits] [llvm] r96688 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Dan Gohman]

Author: djg
Date: Fri Feb 19 12:49:22 2010
New Revision: 96688

URL: http://llvm.org/viewvc/llvm-project?rev=96688&view=rev
Log:
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Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=96688&r1=96687&r2=96688&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Feb 19 12:49:22 2010
@@ -1973,6 +1973,12 @@
     return getAddRecExpr(Operands, L, HasNUW, HasNSW); // {X,+,0}  -->  X
   }
 
+  // It's tempting to want to call getMaxBackedgeTakenCount count here and
+  // use that information to infer NUW and NSW flags. However, computing a
+  // BE count requires calling getAddRecExpr, so we may not yet have a
+  // meaningful BE count at this point (and if we don't, we'd be stuck
+  // with a SCEVCouldNotCompute as the cached BE count).
+
   // If HasNSW is true and all the operands are non-negative, infer HasNUW.
   if (!HasNUW && HasNSW) {
     bool All = true;