SCCIteratorTest.cpp
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//===----- llvm/unittest/ADT/SCCIteratorTest.cpp - SCCIterator tests ------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SCCIterator.h"
#include "TestGraph.h"
#include "gtest/gtest.h"
#include <limits.h>
using namespace llvm;
namespace llvm {
TEST(SCCIteratorTest, AllSmallGraphs) {
// Test SCC computation against every graph with NUM_NODES nodes or less.
// Since SCC considers every node to have an implicit self-edge, we only
// create graphs for which every node has a self-edge.
#define NUM_NODES 4
#define NUM_GRAPHS (NUM_NODES * (NUM_NODES - 1))
typedef Graph<NUM_NODES> GT;
/// Enumerate all graphs using NUM_GRAPHS bits.
static_assert(NUM_GRAPHS < sizeof(unsigned) * CHAR_BIT, "Too many graphs!");
for (unsigned GraphDescriptor = 0; GraphDescriptor < (1U << NUM_GRAPHS);
++GraphDescriptor) {
GT G;
// Add edges as specified by the descriptor.
unsigned DescriptorCopy = GraphDescriptor;
for (unsigned i = 0; i != NUM_NODES; ++i)
for (unsigned j = 0; j != NUM_NODES; ++j) {
// Always add a self-edge.
if (i == j) {
G.AddEdge(i, j);
continue;
}
if (DescriptorCopy & 1)
G.AddEdge(i, j);
DescriptorCopy >>= 1;
}
// Test the SCC logic on this graph.
/// NodesInSomeSCC - Those nodes which are in some SCC.
GT::NodeSubset NodesInSomeSCC;
for (scc_iterator<GT> I = scc_begin(G), E = scc_end(G); I != E; ++I) {
const std::vector<GT::NodeType *> &SCC = *I;
// Get the nodes in this SCC as a NodeSubset rather than a vector.
GT::NodeSubset NodesInThisSCC;
for (unsigned i = 0, e = SCC.size(); i != e; ++i)
NodesInThisSCC.AddNode(SCC[i]->first);
// There should be at least one node in every SCC.
EXPECT_FALSE(NodesInThisSCC.isEmpty());
// Check that every node in the SCC is reachable from every other node in
// the SCC.
for (unsigned i = 0; i != NUM_NODES; ++i)
if (NodesInThisSCC.count(i)) {
EXPECT_TRUE(NodesInThisSCC.isSubsetOf(G.NodesReachableFrom(i)));
}
// OK, now that we now that every node in the SCC is reachable from every
// other, this means that the set of nodes reachable from any node in the
// SCC is the same as the set of nodes reachable from every node in the
// SCC. Check that for every node N not in the SCC but reachable from the
// SCC, no element of the SCC is reachable from N.
for (unsigned i = 0; i != NUM_NODES; ++i)
if (NodesInThisSCC.count(i)) {
GT::NodeSubset NodesReachableFromSCC = G.NodesReachableFrom(i);
GT::NodeSubset ReachableButNotInSCC =
NodesReachableFromSCC.Meet(NodesInThisSCC.Complement());
for (unsigned j = 0; j != NUM_NODES; ++j)
if (ReachableButNotInSCC.count(j)) {
EXPECT_TRUE(G.NodesReachableFrom(j).Meet(NodesInThisSCC).isEmpty());
}
// The result must be the same for all other nodes in this SCC, so
// there is no point in checking them.
break;
}
// This is indeed a SCC: a maximal set of nodes for which each node is
// reachable from every other.
// Check that we didn't already see this SCC.
EXPECT_TRUE(NodesInSomeSCC.Meet(NodesInThisSCC).isEmpty());
NodesInSomeSCC = NodesInSomeSCC.Join(NodesInThisSCC);
// Check a property that is specific to the LLVM SCC iterator and
// guaranteed by it: if a node in SCC S1 has an edge to a node in
// SCC S2, then S1 is visited *after* S2. This means that the set
// of nodes reachable from this SCC must be contained either in the
// union of this SCC and all previously visited SCC's.
for (unsigned i = 0; i != NUM_NODES; ++i)
if (NodesInThisSCC.count(i)) {
GT::NodeSubset NodesReachableFromSCC = G.NodesReachableFrom(i);
EXPECT_TRUE(NodesReachableFromSCC.isSubsetOf(NodesInSomeSCC));
// The result must be the same for all other nodes in this SCC, so
// there is no point in checking them.
break;
}
}
// Finally, check that the nodes in some SCC are exactly those that are
// reachable from the initial node.
EXPECT_EQ(NodesInSomeSCC, G.NodesReachableFrom(0));
}
}
}