When rewriting the pointer operand to a load or store which has
alignment guarantees attached, re-compute the alignment so that we
consider offsets which impact alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164690 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SROA.cpp b/lib/Transforms/Scalar/SROA.cpp
index f1cb947..67246a5 100644
--- a/lib/Transforms/Scalar/SROA.cpp
+++ b/lib/Transforms/Scalar/SROA.cpp
@@ -1992,6 +1992,9 @@
     Value *NewPtr = getAdjustedAllocaPtr(IRB,
                                          LI.getPointerOperand()->getType());
     LI.setOperand(0, NewPtr);
+    if (LI.getAlignment())
+      LI.setAlignment(MinAlign(NewAI.getAlignment(),
+                               BeginOffset - NewAllocaBeginOffset));
     DEBUG(dbgs() << "          to: " << LI << "\n");
 
     deleteIfTriviallyDead(OldOp);
@@ -2043,6 +2046,9 @@
     Value *NewPtr = getAdjustedAllocaPtr(IRB,
                                          SI.getPointerOperand()->getType());
     SI.setOperand(1, NewPtr);
+    if (SI.getAlignment())
+      SI.setAlignment(MinAlign(NewAI.getAlignment(),
+                               BeginOffset - NewAllocaBeginOffset));
     DEBUG(dbgs() << "          to: " << SI << "\n");
 
     deleteIfTriviallyDead(OldOp);