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Fix MemoryDependenceAnalysis in cases where QueryInstr is a CmpXchg or a AtomicRMW

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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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216940 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Robin Morisset 2014-09-02 20:17:52 +00:00
parent 4211bbc568
commit cc99164448
1 changed files with 12 additions and 4 deletions
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16
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -449,12 +449,16 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
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 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
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);
}