[MemorySSA] Update MSSA for non-conventional AA.

Summary:
Regularly when moving an instruction that may not read or write memory,
the instruction is not modelled in MSSA, so not action is necessary.
For a non-conventional AA pipeline, MSSA needs to explicitly check when
creating accesses, so as to not model instructions that may not read and
write memory.

Reviewers: george.burgess.iv

Subscribers: Prazek, sanjoy.google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67562

llvm-svn: 372137

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/MemorySSA.cpp b/llvm/lib/Analysis/MemorySSA.cpp
index db12fcee3ef..cc3bca1c231 100644
--- a/llvm/lib/Analysis/MemorySSA.cpp
+++ b/llvm/lib/Analysis/MemorySSA.cpp
@@ -1736,9 +1736,15 @@ MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I,
   // FIXME: Replace this special casing with a more accurate modelling of
   // assume's control dependency.
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
-    if (II->getIntrinsicID() == Intrinsic::assume || isa<DbgInfoIntrinsic>(II))
+    if (II->getIntrinsicID() == Intrinsic::assume)
       return nullptr;
 
+  // Using a nonstandard AA pipelines might leave us with unexpected modref
+  // results for I, so add a check to not model instructions that may not read
+  // from or write to memory. This is necessary for correctness.
+  if (!I->mayReadFromMemory() && !I->mayWriteToMemory())
+    return nullptr;
+
   bool Def, Use;
   if (Template) {
     Def = dyn_cast_or_null<MemoryDef>(Template) != nullptr;