Fix ScalarEvolution's backedge-taken count computations to check for

overflow when computing a integer division to round up.

Thanks to Nick Lewycky for noticing this!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73862 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/include/llvm/Analysis/ScalarEvolution.h b/include/llvm/Analysis/ScalarEvolution.h
index 211c0ca..8578958 100644
--- a/include/llvm/Analysis/ScalarEvolution.h
+++ b/include/llvm/Analysis/ScalarEvolution.h
@@ -332,6 +332,13 @@ namespace llvm {
                                           const SCEVHandle &SymName,
                                           const SCEVHandle &NewVal);
 
+    /// getBECount - Subtract the end and start values and divide by the step,
+    /// rounding up, to get the number of times the backedge is executed. Return
+    /// CouldNotCompute if an intermediate computation overflows.
+    SCEVHandle getBECount(const SCEVHandle &Start,
+                          const SCEVHandle &End,
+                          const SCEVHandle &Step);
+
     /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
     /// loop, lazily computing new values if the loop hasn't been analyzed
     /// yet.