[AliasAnalysis] Give back AA results for fence instructions
Calling getModRefInfo with a fence resulted in crashes because fences
don't have a memory location. Add a new predicate to Instruction
called isFenceLike which indicates that the instruction mutates memory
but not any single memory location in particular. In practice, it is a
proxy for the set of instructions which "mayWriteToMemory" but cannot be
used with MemoryLocation::get.
This fixes PR28570.
llvm-svn: 275581
diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index 0aed133..f93917f 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -1252,7 +1252,7 @@
// Conservatively, fences are always clobbers, so don't perform the walk if we
// hit a fence.
- if (isa<FenceInst>(I))
+ if (!ImmutableCallSite(I) && I->isFenceLike())
return StartingUseOrDef;
UpwardsMemoryQuery Q;
@@ -1287,15 +1287,17 @@
// access, since we only map BB's to PHI's. So, this must be a use or def.
auto *StartingAccess = cast<MemoryUseOrDef>(MSSA->getMemoryAccess(I));
- // We can't sanely do anything with a FenceInst, they conservatively
+ bool IsCall = bool(ImmutableCallSite(I));
+
+ // We can't sanely do anything with a fences, they conservatively
// clobber all memory, and have no locations to get pointers from to
- // try to disambiguate
- if (isa<FenceInst>(I))
+ // try to disambiguate.
+ if (!IsCall && I->isFenceLike())
return StartingAccess;
UpwardsMemoryQuery Q;
Q.OriginalAccess = StartingAccess;
- Q.IsCall = bool(ImmutableCallSite(I));
+ Q.IsCall = IsCall;
if (!Q.IsCall)
Q.StartingLoc = MemoryLocation::get(I);
Q.Inst = I;