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[LCG] Teach the ref edge removal to handle a ref edge that is trivial

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due to a call cycle.

This actually crashed the ref removal before.

I've added a unittest that covers this kind of interesting graph
structure and mutation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290645 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2016-12-28 02:24:58 +00:00
parent effab69f94
commit 3ab88a9f0d
2 changed files with 85 additions and 1 deletions
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8
lib/Analysis/LazyCallGraph.cpp
View File

@ -1117,6 +1117,13 @@ LazyCallGraph::RefSCC::removeInternalRefEdge(Node &SourceN, Node &TargetN) {
if (&SourceN == &TargetN)
return Result;
// If this ref edge is within an SCC then there are sufficient other edges to
// form a cycle without this edge so removing it is a no-op.
SCC &SourceC = *G->lookupSCC(SourceN);
SCC &TargetC = *G->lookupSCC(TargetN);
if (&SourceC == &TargetC)
return Result;
// We build somewhat synthetic new RefSCCs by providing a postorder mapping
// for each inner SCC. We also store these associated with *nodes* rather
// than SCCs because this saves a round-trip through the node->SCC map and in
@ -1139,7 +1146,6 @@ LazyCallGraph::RefSCC::removeInternalRefEdge(Node &SourceN, Node &TargetN) {
// and handle participants in that cycle without walking all the edges that
// form the connections, and instead by relying on the fundamental guarantee
// coming into this operation.
SCC &TargetC = *G->lookupSCC(TargetN);
for (Node &N : TargetC)
PostOrderMapping[&N] = RootPostOrderNumber;

78
unittests/Analysis/LazyCallGraphTest.cpp
View File

@ -1600,6 +1600,84 @@ TEST(LazyCallGraphTest, InternalEdgeRemoval) {
EXPECT_EQ(E, J);
}
TEST(LazyCallGraphTest, InternalNoOpEdgeRemoval) {
LLVMContext Context;
// A graph with a single cycle formed both from call and reference edges
// which makes the reference edges trivial to delete. The graph looks like:
//
// Reference edges: a -> b -> c -> a
// Call edges: a -> c -> b -> a
std::unique_ptr<Module> M = parseAssembly(
Context, "define void @a(i8** %ptr) {\n"
"entry:\n"
" call void @b(i8** %ptr)\n"
" store i8* bitcast (void(i8**)* @c to i8*), i8** %ptr\n"
" ret void\n"
"}\n"
"define void @b(i8** %ptr) {\n"
"entry:\n"
" store i8* bitcast (void(i8**)* @a to i8*), i8** %ptr\n"
" call void @c(i8** %ptr)\n"
" ret void\n"
"}\n"
"define void @c(i8** %ptr) {\n"
"entry:\n"
" call void @a(i8** %ptr)\n"
" store i8* bitcast (void(i8**)* @b to i8*), i8** %ptr\n"
" ret void\n"
"}\n");
LazyCallGraph CG(*M);
// Force the graph to be fully expanded.
auto I = CG.postorder_ref_scc_begin(), E = CG.postorder_ref_scc_end();
LazyCallGraph::RefSCC &RC = *I;
EXPECT_EQ(E, std::next(I));
LazyCallGraph::SCC &C = *RC.begin();
EXPECT_EQ(RC.end(), std::next(RC.begin()));
LazyCallGraph::Node &AN = *CG.lookup(lookupFunction(*M, "a"));
LazyCallGraph::Node &BN = *CG.lookup(lookupFunction(*M, "b"));
LazyCallGraph::Node &CN = *CG.lookup(lookupFunction(*M, "c"));
EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
EXPECT_EQ(&C, CG.lookupSCC(AN));
EXPECT_EQ(&C, CG.lookupSCC(BN));
EXPECT_EQ(&C, CG.lookupSCC(CN));
// Remove the edge from a -> c which doesn't change anything.
SmallVector<LazyCallGraph::RefSCC *, 1> NewRCs =
RC.removeInternalRefEdge(AN, CN);
EXPECT_EQ(0u, NewRCs.size());
EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
EXPECT_EQ(&C, CG.lookupSCC(AN));
EXPECT_EQ(&C, CG.lookupSCC(BN));
EXPECT_EQ(&C, CG.lookupSCC(CN));
auto J = CG.postorder_ref_scc_begin();
EXPECT_EQ(I, J);
EXPECT_EQ(&RC, &*J);
EXPECT_EQ(E, std::next(J));
// Remove the edge from b -> a and c -> b; again this doesn't change
// anything.
NewRCs = RC.removeInternalRefEdge(BN, AN);
NewRCs = RC.removeInternalRefEdge(CN, BN);
EXPECT_EQ(0u, NewRCs.size());
EXPECT_EQ(&RC, CG.lookupRefSCC(AN));
EXPECT_EQ(&RC, CG.lookupRefSCC(BN));
EXPECT_EQ(&RC, CG.lookupRefSCC(CN));
EXPECT_EQ(&C, CG.lookupSCC(AN));
EXPECT_EQ(&C, CG.lookupSCC(BN));
EXPECT_EQ(&C, CG.lookupSCC(CN));
J = CG.postorder_ref_scc_begin();
EXPECT_EQ(I, J);
EXPECT_EQ(&RC, &*J);
EXPECT_EQ(E, std::next(J));
}
TEST(LazyCallGraphTest, InternalCallEdgeToRef) {
LLVMContext Context;
// A nice fully connected (including self-edges) SCC (and RefSCC)