Fix MemoryDependenceAnalysis in cases where QueryInstr is a CmpXchg or a AtomicRMW
Summary:
MemoryDependenceAnalysis is currently cautious when the QueryInstr is an atomic
load or store, but I forgot to check for atomic cmpxchg/atomicrmw. This patch
is a way of fixing that, and making it less brittle (i.e. no risk that I forget
another possible kind of atomic, even if the IR ends up changing in the future),
by adding a fallback checking mayReadOrWriteFromMemory.
Thanks to Philip Reames for finding this bug and suggesting this solution in
http://reviews.llvm.org/D4845
Sadly, I don't see how to add a test for this, since the passes depending on
MemoryDependenceAnalysis won't trigger for an atomic rmw anyway. Does anyone
see a way for testing it?
Test Plan: none possible at first sight
Reviewers: jfb, reames
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D5019
llvm-svn: 216940
diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index aef2418..f7180aa 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -449,12 +449,16 @@
if (!LI->isUnordered()) {
if (!QueryInst)
return MemDepResult::getClobber(LI);
- if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+ if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst)) {
if (!QueryLI->isSimple())
return MemDepResult::getClobber(LI);
- if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+ } else if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst)) {
if (!QuerySI->isSimple())
return MemDepResult::getClobber(LI);
+ } else if (QueryInst->mayReadOrWriteMemory()) {
+ return MemDepResult::getClobber(LI);
+ }
+
if (isAtLeastAcquire(LI->getOrdering()))
HasSeenAcquire = true;
}
@@ -529,12 +533,16 @@
if (!SI->isUnordered()) {
if (!QueryInst)
return MemDepResult::getClobber(SI);
- if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+ if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst)) {
if (!QueryLI->isSimple())
return MemDepResult::getClobber(SI);
- if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+ } else if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst)) {
if (!QuerySI->isSimple())
return MemDepResult::getClobber(SI);
+ } else if (QueryInst->mayReadOrWriteMemory()) {
+ return MemDepResult::getClobber(SI);
+ }
+
if (HasSeenAcquire && isAtLeastRelease(SI->getOrdering()))
return MemDepResult::getClobber(SI);
}