getSmallConstantTripMultiple should never return zero.

When the trip count is -1, getSmallConstantTripMultiple could return zero,
and this would cause runtime loop unrolling to assert. Instead of returning
zero, one is now returned (consistent with the existing overflow cases).
Fixes PR14167.

llvm-svn: 166612

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 3e062988823..148912b766b 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3979,8 +3979,11 @@ getSmallConstantTripMultiple(Loop *L, BasicBlock *ExitingBlock) {
 
   ConstantInt *Result = MulC->getValue();
 
-  // Guard against huge trip counts.
-  if (!Result || Result->getValue().getActiveBits() > 32)
+  // Guard against huge trip counts (this requires checking
+  // for zero to handle the case where the trip count == -1 and the
+  // addition wraps).
+  if (!Result || Result->getValue().getActiveBits() > 32 ||
+      Result->getValue().getActiveBits() == 0)
     return 1;
 
   return (unsigned)Result->getZExtValue();