From: Dan Gohman <gohman@apple.com>
Date: Sat, 20 Jun 2009 00:32:22 +0000 (+0000)
Subject: Use ScalarEvolution's new GetMinSignBits and GetMinLeadingZeros
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3964acc2f44ee02cdd4e2a54a5232537bdf3ee73;p=oota-llvm.git

Use ScalarEvolution's new GetMinSignBits and GetMinLeadingZeros
in the loop backedge-taken count computation of the maximum
possible trip count.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73805 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 2dab2f367de..465807ecacb 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3836,9 +3836,12 @@ HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
                      : 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.