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[LCG] Implement Tarjan's algorithm correctly this time. We have to walk

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up the stack finishing the exploration of each entries children before
we're finished in addition to accounting for their low-links. Added
a unittest that really hammers home the need for this with interlocking
cycles that would each appear distinct otherwise and crash or compute
the wrong result. As part of this, nuke a stale fixme and bring the rest
of the implementation still more closely in line with the original
algorithm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206966 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2014-04-23 10:31:17 +00:00
parent 57683b8aba
commit b9619110af
3 changed files with 100 additions and 34 deletions
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57
unittests/Analysis/LazyCallGraphTest.cpp
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@ -248,4 +248,61 @@ TEST(LazyCallGraphTest, BasicGraphFormation) {
EXPECT_EQ(CG.postorder_scc_end(), SCCI);
}
static Function &lookupFunction(Module &M, StringRef Name) {
for (Function &F : M)
if (F.getName() == Name)
return F;
report_fatal_error("Couldn't find function!");
}
TEST(LazyCallGraphTest, MultiArmSCC) {
// Two interlocking cycles. The really useful thing about this SCC is that it
// will require Tarjan's DFS to backtrack and finish processing all of the
// children of each node in the SCC.
std::unique_ptr<Module> M = parseAssembly(
"define void @a() {\n"
"entry:\n"
" call void @b()\n"
" call void @d()\n"
" ret void\n"
"}\n"
"define void @b() {\n"
"entry:\n"
" call void @c()\n"
" ret void\n"
"}\n"
"define void @c() {\n"
"entry:\n"
" call void @a()\n"
" ret void\n"
"}\n"
"define void @d() {\n"
"entry:\n"
" call void @e()\n"
" ret void\n"
"}\n"
"define void @e() {\n"
"entry:\n"
" call void @a()\n"
" ret void\n"
"}\n");
LazyCallGraph CG(*M);
// Force the graph to be fully expanded.
auto SCCI = CG.postorder_scc_begin();
LazyCallGraph::SCC *SCC = *SCCI++;
EXPECT_EQ(CG.postorder_scc_end(), SCCI);
LazyCallGraph::Node *A = CG.lookup(lookupFunction(*M, "a"));
LazyCallGraph::Node *B = CG.lookup(lookupFunction(*M, "b"));
LazyCallGraph::Node *C = CG.lookup(lookupFunction(*M, "c"));
LazyCallGraph::Node *D = CG.lookup(lookupFunction(*M, "d"));
LazyCallGraph::Node *E = CG.lookup(lookupFunction(*M, "e"));
EXPECT_EQ(SCC, CG.lookupSCC(A->getFunction()));
EXPECT_EQ(SCC, CG.lookupSCC(B->getFunction()));
EXPECT_EQ(SCC, CG.lookupSCC(C->getFunction()));
EXPECT_EQ(SCC, CG.lookupSCC(D->getFunction()));
EXPECT_EQ(SCC, CG.lookupSCC(E->getFunction()));
}
}