6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-06-20 10:24:12 +00:00
Code Issues Projects Releases Wiki Activity

MemoryDependenceAnalysis: Don't miscompile atomics

Browse Source 
r216771 introduced a change to MemoryDependenceAnalysis that allowed it
to reason about acquire/release operations.  However, this change does
not ensure that the acquire/release operations pair.  Unfortunately,
this leads to miscompiles as we won't see an acquire load as properly
memory effecting.  This largely reverts r216771.

This fixes PR22708.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232889 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2015-03-21 06:19:17 +00:00
parent 048ca17f6e
commit ac5b42cad8
3 changed files with 21 additions and 96 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -407,7 +407,6 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
// by every program that can detect any optimisation of that kind: either
// it is racy (undefined) or there is a release followed by an acquire
// between the pair of accesses under consideration.
bool HasSeenAcquire = false;
if (isLoad && QueryInst) {
LoadInst *LI = dyn_cast<LoadInst>(QueryInst);
@ -468,12 +467,12 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
// Atomic loads have complications involved.
// A Monotonic (or higher) load is OK if the query inst is itself not atomic.
// An Acquire (or higher) load sets the HasSeenAcquire flag, so that any
// release store will know to return getClobber.
// FIXME: This is overly conservative.
if (LI->isAtomic() && LI->getOrdering() > Unordered) {
if (!QueryInst)
return MemDepResult::getClobber(LI);
if (LI->getOrdering() != Monotonic)
return MemDepResult::getClobber(LI);
if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst)) {
if (!QueryLI->isSimple())
return MemDepResult::getClobber(LI);
@ -483,9 +482,6 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
} else if (QueryInst->mayReadOrWriteMemory()) {
return MemDepResult::getClobber(LI);
}
if (isAtLeastAcquire(LI->getOrdering()))
HasSeenAcquire = true;
}
AliasAnalysis::Location LoadLoc = AA->getLocation(LI);
@ -545,12 +541,12 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
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.
// A Release (or higher) store further requires that no acquire load
// has been seen.
// FIXME: This is overly conservative.
if (!SI->isUnordered()) {
if (!QueryInst)
return MemDepResult::getClobber(SI);
if (SI->getOrdering() != Monotonic)
return MemDepResult::getClobber(SI);
if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst)) {
if (!QueryLI->isSimple())
return MemDepResult::getClobber(SI);
@ -560,9 +556,6 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
} else if (QueryInst->mayReadOrWriteMemory()) {
return MemDepResult::getClobber(SI);
}
if (HasSeenAcquire && isAtLeastRelease(SI->getOrdering()))
return MemDepResult::getClobber(SI);
}
// FIXME: this is overly conservative.