CodeGen: Don't drop AA metadata when splitting MachineMemOperands

Assuming this is used to split a memory access into smaller pieces,
the new access should still have the same aliasing properties as the
original memory access. As far as I can tell, this wasn't
intentionally dropped. It may be necessary to drop this if you are
moving the operand outside of the bounds of the original object in
such a way that it may alias another IR object, but I don't think any
of the existing users are doing this. Some of the uses widen into
unused alignment padding, which I think is OK.

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index abf4784..0950d64 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -492,9 +492,11 @@ MachineFunction::getMachineMemOperand(const MachineMemOperand *MMO,
                         ? commonAlignment(MMO->getBaseAlign(), Offset)
                         : MMO->getBaseAlign();
 
+  // Do not preserve ranges, since we don't necessarily know what the high bits
+  // are anymore.
   return new (Allocator)
       MachineMemOperand(PtrInfo.getWithOffset(Offset), MMO->getFlags(), Size,
-                        Alignment, AAMDNodes(), nullptr, MMO->getSyncScopeID(),
+                        Alignment, MMO->getAAInfo(), nullptr, MMO->getSyncScopeID(),
                         MMO->getOrdering(), MMO->getFailureOrdering());
 }