[LoopIdiom] check for safety while expanding

Loop Idiom recognition was generating memset in a case that
would result generating a division operation to an unsafe location.

Differential Revision: https://reviews.llvm.org/D32674

llvm-svn: 302238

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index 410fbb03068..48d5ae88cda 100644
--- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -783,6 +783,11 @@ bool LoopIdiomRecognize::processLoopStridedStore(
   if (NegStride)
     Start = getStartForNegStride(Start, BECount, IntPtr, StoreSize, SE);
 
+  // TODO: ideally we should still be able to generate memset if SCEV expander
+  // is taught to generate the dependencies at the latest point.
+  if (!isSafeToExpand(Start, *SE))
+    return false;
+
   // Okay, we have a strided store "p[i]" of a splattable value.  We can turn
   // this into a memset in the loop preheader now if we want.  However, this
   // would be unsafe to do if there is anything else in the loop that may read
@@ -814,6 +819,11 @@ bool LoopIdiomRecognize::processLoopStridedStore(
                                SCEV::FlagNUW);
   }
 
+  // TODO: ideally we should still be able to generate memset if SCEV expander
+  // is taught to generate the dependencies at the latest point.
+  if (!isSafeToExpand(NumBytesS, *SE))
+    return false;
+
   Value *NumBytes =
       Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());