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[CallGraphUpdater] Properly remove strongly connected components (oldPM)

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Summary:
The old code did eliminate references from and to functions that were
about to be deleted only just before we deleted them. This can cause
references from other functions that are supposed to be deleted to still
exist, depending on the order. If the functions form a strongly
connected component the problem manifests regardless of the order in
which we try to actually delete the functions.

This patch introduces a two step deletion. First we remove all
references and then we delete the function. Note that this only affects
the old call graph. There should not be any functional changes if no old
style call graph was given.

To test this we delete two strongly connected functions instead of one
in an existing test.

Reviewers: hfinkel

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77975
This commit is contained in:
Johannes Doerfert 2020-04-12 11:52:06 -05:00
parent 8901ccbcf6
commit 46d3056c40
2 changed files with 73 additions and 45 deletions
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83
lib/Transforms/Utils/CallGraphUpdater.cpp
View File

@ -26,49 +26,56 @@ bool CallGraphUpdater::finalize() {
DeadFunctionsInComdats.end());
}
for (Function *DeadFn : DeadFunctions) {
DeadFn->removeDeadConstantUsers();
if (CG) {
// First remove all references, e.g., outgoing via called functions. This is
// necessary as we can delete functions that have circular references.
for (Function *DeadFn : DeadFunctions) {
DeadFn->removeDeadConstantUsers();
CallGraphNode *DeadCGN = (*CG)[DeadFn];
DeadCGN->removeAllCalledFunctions();
CG->getExternalCallingNode()->removeAnyCallEdgeTo(DeadCGN);
DeadFn->replaceAllUsesWith(UndefValue::get(DeadFn->getType()));
}
if (CG) {
CallGraphNode *OldCGN = CG->getOrInsertFunction(DeadFn);
CG->getExternalCallingNode()->removeAnyCallEdgeTo(OldCGN);
OldCGN->removeAllCalledFunctions();
// Then remove the node and function from the module.
for (Function *DeadFn : DeadFunctions) {
CallGraphNode *DeadCGN = CG->getOrInsertFunction(DeadFn);
assert(DeadCGN->getNumReferences() == 0 &&
"References should have been handled by now");
delete CG->removeFunctionFromModule(DeadCGN);
}
} else {
// This is the code path for the new lazy call graph and for the case were
// no call graph was provided.
for (Function *DeadFn : DeadFunctions) {
DeadFn->removeDeadConstantUsers();
DeadFn->replaceAllUsesWith(UndefValue::get(DeadFn->getType()));
assert(OldCGN->getNumReferences() == 0);
if (LCG && !ReplacedFunctions.count(DeadFn)) {
// Taken mostly from the inliner:
LazyCallGraph::Node &N = LCG->get(*DeadFn);
auto *DeadSCC = LCG->lookupSCC(N);
assert(DeadSCC && DeadSCC->size() == 1 &&
&DeadSCC->begin()->getFunction() == DeadFn);
auto &DeadRC = DeadSCC->getOuterRefSCC();
delete CG->removeFunctionFromModule(OldCGN);
continue;
FunctionAnalysisManager &FAM =
AM->getResult<FunctionAnalysisManagerCGSCCProxy>(*DeadSCC, *LCG)
.getManager();
FAM.clear(*DeadFn, DeadFn->getName());
AM->clear(*DeadSCC, DeadSCC->getName());
LCG->removeDeadFunction(*DeadFn);
// Mark the relevant parts of the call graph as invalid so we don't
// visit them.
UR->InvalidatedSCCs.insert(DeadSCC);
UR->InvalidatedRefSCCs.insert(&DeadRC);
}
// The function is now really dead and de-attached from everything.
DeadFn->eraseFromParent();
}
// The old style call graph (CG) has a value handle we do not want to
// replace with undef so we do this here.
DeadFn->replaceAllUsesWith(UndefValue::get(DeadFn->getType()));
if (LCG && !ReplacedFunctions.count(DeadFn)) {
// Taken mostly from the inliner:
LazyCallGraph::Node &N = LCG->get(*DeadFn);
auto *DeadSCC = LCG->lookupSCC(N);
assert(DeadSCC && DeadSCC->size() == 1 &&
&DeadSCC->begin()->getFunction() == DeadFn);
auto &DeadRC = DeadSCC->getOuterRefSCC();
FunctionAnalysisManager &FAM =
AM->getResult<FunctionAnalysisManagerCGSCCProxy>(*DeadSCC, *LCG)
.getManager();
FAM.clear(*DeadFn, DeadFn->getName());
AM->clear(*DeadSCC, DeadSCC->getName());
LCG->removeDeadFunction(*DeadFn);
// Mark the relevant parts of the call graph as invalid so we don't visit
// them.
UR->InvalidatedSCCs.insert(DeadSCC);
UR->InvalidatedRefSCCs.insert(&DeadRC);
}
// The function is now really dead and de-attached from everything.
DeadFn->eraseFromParent();
}
bool Changed = !DeadFunctions.empty();

35
unittests/IR/LegacyPassManagerTest.cpp
View File

@ -560,6 +560,21 @@ namespace llvm {
return mod;
}
/// Split a simple function which contains only a call and a return into two
/// such that the first calls the second and the second whoever was called
/// initially.
Function *splitSimpleFunction(Function &F) {
LLVMContext &Context = F.getContext();
Function *SF = Function::Create(F.getFunctionType(), F.getLinkage(),
F.getName() + "b", F.getParent());
F.setName(F.getName() + "a");
BasicBlock *Entry = BasicBlock::Create(Context, "entry", SF, nullptr);
CallInst &CI = cast<CallInst>(F.getEntryBlock().front());
CI.clone()->insertBefore(ReturnInst::Create(Context, Entry));
CI.setCalledFunction(SF);
return SF;
}
struct CGModifierPass : public CGPass {
unsigned NumSCCs = 0;
unsigned NumFns = 0;
@ -582,7 +597,8 @@ namespace llvm {
Function *F = N->getFunction();
Module *M = F->getParent();
Function *Test1F = M->getFunction("test1");
Function *Test2F = M->getFunction("test2");
Function *Test2aF = M->getFunction("test2a");
Function *Test2bF = M->getFunction("test2b");
Function *Test3F = M->getFunction("test3");
auto InSCC = [&](Function *Fn) {
return llvm::any_of(SCMM, [Fn](CallGraphNode *CGN) {
@ -590,18 +606,19 @@ namespace llvm {
});
};
if (!Test1F || !Test2F || !Test3F || !InSCC(Test1F) || !InSCC(Test2F) ||
!InSCC(Test3F))
if (!Test1F || !Test2aF || !Test2bF || !Test3F || !InSCC(Test1F) ||
!InSCC(Test2aF) || !InSCC(Test2bF) || !InSCC(Test3F))
return SetupWorked = false;
CallInst *CI = dyn_cast<CallInst>(&Test1F->getEntryBlock().front());
if (!CI || CI->getCalledFunction() != Test2F)
if (!CI || CI->getCalledFunction() != Test2aF)
return SetupWorked = false;
CI->setCalledFunction(Test3F);
CGU.initialize(const_cast<CallGraph &>(SCMM.getCallGraph()), SCMM);
CGU.removeFunction(*Test2F);
CGU.removeFunction(*Test2aF);
CGU.removeFunction(*Test2bF);
CGU.reanalyzeFunction(*Test1F);
return true;
}
@ -610,20 +627,24 @@ namespace llvm {
};
TEST(PassManager, CallGraphUpdater0) {
// SCC#1: test1->test2->test3->test1
// SCC#1: test1->test2a->test2b->test3->test1
// SCC#2: test4
// SCC#3: indirect call node
LLVMContext Context;
std::unique_ptr<Module> M(makeLLVMModule(Context));
ASSERT_EQ(M->getFunctionList().size(), 4U);
Function *F = M->getFunction("test2");
Function *SF = splitSimpleFunction(*F);
CallInst::Create(F, "", &SF->getEntryBlock());
ASSERT_EQ(M->getFunctionList().size(), 5U);
CGModifierPass *P = new CGModifierPass();
legacy::PassManager Passes;
Passes.add(P);
Passes.run(*M);
ASSERT_TRUE(P->SetupWorked);
ASSERT_EQ(P->NumSCCs, 3U);
ASSERT_EQ(P->NumFns, 4U);
ASSERT_EQ(P->NumFns, 5U);
ASSERT_EQ(M->getFunctionList().size(), 3U);
}
}