Make getModRefInfo more consistent for loads/stores and cmpxchg/atomicrmw

[george.burgess.iv]

Summary

Hi!

When looking through lib/Analysis/AliasAnalysis.cpp, I noticed that we always answer conservatively for volatile loads/stores, but we don't necessarily do this for cmpxchg/atomicrmw. This seems inconsistent to me, so I'd like to know if it was intentional. If not, here's a patch to fix it. :)

The change is fairly insignificant/I can't get it to fire with a lit test, so no test is included. If we'd like one, I'm happy to see what I can do with gtest.

lib/Analysis/AliasAnalysis.cpp

ModRefInfo AAResults::getModRefInfo(const CatchReturnInst *CatchRet,
 
   // Otherwise, a catchret reads and writes.
   return MRI_ModRef;
 }
 
 ModRefInfo AAResults::getModRefInfo(const AtomicCmpXchgInst *CX,
                                     const MemoryLocation &Loc) {
   // Acquire/Release cmpxchg has properties that matter for arbitrary addresses.
-  if (CX->getSuccessOrdering() > Monotonic)
+  if (CX->getSuccessOrdering() > Monotonic || CX->isVolatile())
     return MRI_ModRef;
 
   // If the cmpxchg address does not alias the location, it does not access it.
   if (Loc.Ptr && !alias(MemoryLocation::get(CX), Loc))
     return MRI_NoModRef;
 
   return MRI_ModRef;
 }
 
 ModRefInfo AAResults::getModRefInfo(const AtomicRMWInst *RMW,
                                     const MemoryLocation &Loc) {
   // Acquire/Release atomicrmw has properties that matter for arbitrary addresses.
-  if (RMW->getOrdering() > Monotonic)
+  if (RMW->getOrdering() > Monotonic || RMW->isVolatile())
     return MRI_ModRef;
 
   // If the atomicrmw address does not alias the location, it does not access it.
   if (Loc.Ptr && !alias(MemoryLocation::get(RMW), Loc))
     return MRI_NoModRef;
 
   return MRI_ModRef;
 }