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"
33 using namespace llvm;
34 
35 namespace {
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 
65 char CFGSCC::ID = 0;
66 static RegisterPass<CFGSCC>
67 Y("print-cfg-sccs", "Print SCCs of each function CFG");
68 
69 char CallGraphSCC::ID = 0;
70 static RegisterPass<CallGraphSCC>
71 Z("print-callgraph-sccs", "Print SCCs of the Call Graph");
72 
73 bool 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.
93 bool 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