1//===- PrintSCC.cpp - Enumerate SCCs in some key graphs -------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file provides passes to print out SCCs in a CFG or a CallGraph.
10// Normally, you would not use these passes; instead, you would use the
11// scc_iterator directly to enumerate SCCs and process them in some way.  These
12// passes serve three purposes:
13//
14// (1) As a reference for how to use the scc_iterator.
15// (2) To print out the SCCs for a CFG or a CallGraph:
16//       analyze -print-cfg-sccs            to print the SCCs in each CFG of a module.
17//       analyze -print-cfg-sccs -stats     to print the #SCCs and the maximum SCC size.
18//       analyze -print-cfg-sccs -debug > /dev/null to watch the algorithm in action.
19//
20//     and similarly:
21//       analyze -print-callgraph-sccs [-stats] [-debug] to print SCCs in the CallGraph
22//
23// (3) To test the scc_iterator.
24//
25//===----------------------------------------------------------------------===//
26
27#include "llvm/ADT/SCCIterator.h"
28#include "llvm/Analysis/CallGraph.h"
29#include "llvm/IR/CFG.h"
30#include "llvm/IR/Module.h"
31#include "llvm/Pass.h"
32#include "llvm/Support/raw_ostream.h"
33using namespace llvm;
34
35namespace {
36  struct CFGSCC : public FunctionPass {
37    static char ID;  // Pass identification, replacement for typeid
38    CFGSCC() : FunctionPass(ID) {}
39    bool runOnFunction(Function& func) override;
40
41    void print(raw_ostream &O, const Module* = nullptr) const override { }
42
43    void getAnalysisUsage(AnalysisUsage &AU) const override {
44      AU.setPreservesAll();
45    }
46  };
47
48  struct CallGraphSCC : public ModulePass {
49    static char ID;  // Pass identification, replacement for typeid
50    CallGraphSCC() : ModulePass(ID) {}
51
52    // run - Print out SCCs in the call graph for the specified module.
53    bool runOnModule(Module &M) override;
54
55    void print(raw_ostream &O, const Module* = nullptr) const override { }
56
57    // getAnalysisUsage - This pass requires the CallGraph.
58    void getAnalysisUsage(AnalysisUsage &AU) const override {
59      AU.setPreservesAll();
60      AU.addRequired<CallGraphWrapperPass>();
61    }
62  };
63}
64
65char CFGSCC::ID = 0;
66static RegisterPass<CFGSCC>
67Y("print-cfg-sccs", "Print SCCs of each function CFG");
68
69char CallGraphSCC::ID = 0;
70static RegisterPass<CallGraphSCC>
71Z("print-callgraph-sccs", "Print SCCs of the Call Graph");
72
73bool CFGSCC::runOnFunction(Function &F) {
74  unsigned sccNum = 0;
75  errs() << "SCCs for Function " << F.getName() << " in PostOrder:";
76  for (scc_iterator<Function*> SCCI = scc_begin(&F); !SCCI.isAtEnd(); ++SCCI) {
77    const std::vector<BasicBlock *> &nextSCC = *SCCI;
78    errs() << "\nSCC #" << ++sccNum << " : ";
79    for (BasicBlock *BB : nextSCC) {
80      BB->printAsOperand(errs(), false);
81      errs() << ", ";
82    }
83    if (nextSCC.size() == 1 && SCCI.hasCycle())
84      errs() << " (Has self-loop).";
85  }
86  errs() << "\n";
87
88  return true;
89}
90
91
92// run - Print out SCCs in the call graph for the specified module.
93bool CallGraphSCC::runOnModule(Module &M) {
94  CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
95  unsigned sccNum = 0;
96  errs() << "SCCs for the program in PostOrder:";
97  for (scc_iterator<CallGraph*> SCCI = scc_begin(&CG); !SCCI.isAtEnd();
98       ++SCCI) {
99    const std::vector<CallGraphNode*> &nextSCC = *SCCI;
100    errs() << "\nSCC #" << ++sccNum << " : ";
101    for (std::vector<CallGraphNode*>::const_iterator I = nextSCC.begin(),
102           E = nextSCC.end(); I != E; ++I)
103      errs() << ((*I)->getFunction() ? (*I)->getFunction()->getName()
104                                     : "external node") << ", ";
105    if (nextSCC.size() == 1 && SCCI.hasCycle())
106      errs() << " (Has self-loop).";
107  }
108  errs() << "\n";
109
110  return true;
111}
112