[AliasAnalysis] getModRefInfo(DetachInst *, MemoryLocation &) unnecessarily superlinear time, unnecessarily recursive. about tapir-llvm

[VictorYing]

Here's a more recent version that still has the same problem:

Tapir-LLVM/lib/Analysis/AliasAnalysis.cpp

Lines 657 to 694 in a038195

	ModRefInfo AAResults::getModRefInfo(const DetachInst *D,
	const MemoryLocation &Loc) {
	ModRefInfo Result = ModRefInfo::NoModRef;
	SmallPtrSet<const BasicBlock *, 32> Visited;
	SmallVector<const BasicBlock *, 32> WorkList;
	WorkList.push_back(D->getDetached());
	while (!WorkList.empty()) {
	const BasicBlock *BB = WorkList.pop_back_val();
	if (!Visited.insert(BB).second)
	continue;
	for (const Instruction &I : *BB) {
	// Ignore sync instructions in this analysis
	if (isa<SyncInst>(I))
	continue;
	// Fail fast if we encounter an invalid CFG.
	assert(!(D == &I) &&
	"Invalid CFG found: Detached CFG reaches its own Detach.");
	Result = unionModRef(Result, getModRefInfo(&I, Loc));
	// Early-exit the moment we reach the top of the lattice.
	if (isModAndRefSet(Result))
	return Result;
	}
	// Add successors
	const Instruction *T = BB->getTerminator();
	if (const ReattachInst *RI = dyn_cast<ReattachInst>(T))
	if (D->getSyncRegion() == RI->getSyncRegion())
	continue;
	for (unsigned idx = 0, max = T->getNumSuccessors(); idx < max; ++idx)
	WorkList.push_back(T->getSuccessor(idx));
	}
	return Result;
	}

It's that

Result = unionModRef(Result, getModRefInfo(&I, Loc)); 

that causes the problem without any checks for whether this I is itself a detach.

[VictorYing]

Elsewhere in the same file, there's a different loop that correctly ignores nested syncs and detaches within a detached CFG:

Tapir-LLVM/lib/Analysis/AliasAnalysis.cpp

Lines 145 to 180 in a038195

	} else if (auto D = dyn_cast<DetachInst>(I)) {
	ModRefInfo Result = ModRefInfo::NoModRef;
	SmallPtrSet<BasicBlock *, 32> Visited;
	SmallVector<BasicBlock *, 32> WorkList;
	WorkList.push_back(D->getDetached());
	while (!WorkList.empty()) {
	BasicBlock *BB = WorkList.pop_back_val();
	if (!Visited.insert(BB).second)
	continue;
	for (Instruction &DI : *BB) {
	// Fail fast if we encounter an invalid CFG.
	assert(!(D == &DI) &&
	"Detached CFG reaches its own Detach instruction.");
	// Ignore sync instructions in this analysis
	if (isa<SyncInst>(DI) || isa<DetachInst>(DI))
	continue;
	if (isa<LoadInst>(DI) || isa<StoreInst>(DI) ||
	isa<AtomicCmpXchgInst>(DI) || isa<AtomicRMWInst>(DI) ||
	DI.isFenceLike() || ImmutableCallSite(&DI))
	Result = unionModRef(Result, getModRefInfo(&DI, Call2));
	if (&DI == Call2)
	return ModRefInfo::NoModRef;
	}
	// Add successors
	const Instruction *T = BB->getTerminator();
	if (const ReattachInst *RI = dyn_cast<ReattachInst>(T))
	if (D->getSyncRegion() == RI->getSyncRegion())
	continue;
	for (unsigned idx = 0, max = T->getNumSuccessors(); idx < max; ++idx)
	WorkList.push_back(T->getSuccessor(idx));
	}
	return Result;

Note the

if (isa<SyncInst>(DI) || isa<DetachInst>(DI))
  continue; 

[VictorYing]

Closed by 83765ec