[llvm-commits] [llvm] r73805 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Dan Gohman]

Author: djg
Date: Fri Jun 19 19:32:22 2009
New Revision: 73805

URL: http://llvm.org/viewvc/llvm-project?rev=73805&view=rev
Log:
Use ScalarEvolution's new GetMinSignBits and GetMinLeadingZeros
in the loop backedge-taken count computation of the maximum
possible trip count.

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=73805&r1=73804&r2=73805&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Jun 19 19:32:22 2009
@@ -3836,9 +3836,12 @@
                      : getUMaxExpr(RHS, Start);
 
     // Determine the maximum constant end value.
-    SCEVHandle MaxEnd = isa<SCEVConstant>(End) ? End :
-      getConstant(isSigned ? APInt::getSignedMaxValue(BitWidth) :
-                             APInt::getMaxValue(BitWidth));
+    SCEVHandle MaxEnd =
+      isa<SCEVConstant>(End) ? End :
+      getConstant(isSigned ? APInt::getSignedMaxValue(BitWidth)
+                               .ashr(GetMinSignBits(End) - 1) :
+                             APInt::getMaxValue(BitWidth)
+                               .lshr(GetMinLeadingZeros(End)));
 
     // Finally, we subtract these two values and divide, rounding up, to get
     // the number of times the backedge is executed.