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