Avoid fusing bitcasts with dynamic allocas if the amount-to-allocate

might overflow.  Re-typing the alloca to a larger type (e.g. double)
hoists a shift into the alloca, potentially exposing overflow in the
expression.  rdar://problem/9265821


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132926 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 199902a..601d9b4 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -71,6 +71,11 @@ Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
   // This requires TargetData to get the alloca alignment and size information.
   if (!TD) return 0;
 
+  // Insist that the amount-to-allocate not overflow.
+  OverflowingBinaryOperator *OBI =
+    dyn_cast<OverflowingBinaryOperator>(AI.getOperand(0));
+  if (OBI && !(OBI->hasNoSignedWrap() || OBI->hasNoUnsignedWrap())) return 0;
+
   const PointerType *PTy = cast<PointerType>(CI.getType());
   
   BuilderTy AllocaBuilder(*Builder);