Weak relaxing of the constraints on atomics in MemoryDependencyAnalysis
Monotonic accesses do not have to kill the analysis, as long as the QueryInstr is not
itself atomic.
llvm-svn: 215942
diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 5966937..33fe425 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -409,9 +409,18 @@
// a load depends on another must aliased load from the same value.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
// Atomic loads have complications involved.
+ // A monotonic load is OK if the query inst is itself not atomic.
// FIXME: This is overly conservative.
- if (!LI->isUnordered())
- return MemDepResult::getClobber(LI);
+ if (!LI->isUnordered()) {
+ if (!QueryInst || LI->getOrdering() != Monotonic)
+ return MemDepResult::getClobber(LI);
+ if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+ if (!QueryLI->isUnordered())
+ return MemDepResult::getClobber(LI);
+ if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+ if (!QuerySI->isUnordered())
+ return MemDepResult::getClobber(LI);
+ }
AliasAnalysis::Location LoadLoc = AA->getLocation(LI);
@@ -469,9 +478,18 @@
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// Atomic stores have complications involved.
+ // A monotonic store is OK if the query inst is itself not atomic.
// FIXME: This is overly conservative.
- if (!SI->isUnordered())
- return MemDepResult::getClobber(SI);
+ if (!SI->isUnordered()) {
+ if (!QueryInst || SI->getOrdering() != Monotonic)
+ return MemDepResult::getClobber(SI);
+ if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+ if (!QueryLI->isUnordered())
+ return MemDepResult::getClobber(SI);
+ if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+ if (!QuerySI->isUnordered())
+ return MemDepResult::getClobber(SI);
+ }
// If alias analysis can tell that this store is guaranteed to not modify
// the query pointer, ignore it. Use getModRefInfo to handle cases where