Fix LoopLoadElimination to keep original alignment on the inital hoisted store

This is fixing a bug where Loop Vectorization is widening a load but
with a lower alignment. Hoisting the load without propagating the alignment
will allow inst-combine to later deduce a higher alignment that what the pointer
actually is.

Differential Revision: https://reviews.llvm.org/D28408

llvm-svn: 291281

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
index 08e7acdaaf7..8fb580183e3 100644
--- a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
@@ -415,7 +415,9 @@ public:
     Value *InitialPtr = SEE.expandCodeFor(PtrSCEV->getStart(), Ptr->getType(),
                                           PH->getTerminator());
     Value *Initial =
-        new LoadInst(InitialPtr, "load_initial", PH->getTerminator());
+        new LoadInst(InitialPtr, "load_initial", /* isVolatile */ false,
+                     Cand.Load->getAlignment(), PH->getTerminator());
+
     PHINode *PHI = PHINode::Create(Initial->getType(), 2, "store_forwarded",
                                    &L->getHeader()->front());
     PHI->addIncoming(Initial, PH);