LLVM Pass 简介（2）

本节介绍一段对LLVM 的Function进行遍历的过程，遍历过程中统计每个Function内的BasicBlock数目和指令数目，同时统计所有的operand出现的次数。

因为涉及到IR的东西，UserManual手册为： https://llvm.org/docs/LangRef.html 。真的建议初学者都去简单的扫一遍这个文档，看下目录也好，网上的很多介绍文档和博客上边都给了很多错误的东西。

#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Function.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <string>
#include "llvm/IR/Instructions.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
using namespace llvm;
#define DEBUG_TYPE "hello"

STATISTIC(HelloCounter, "Counts number of functions greeted");
namespace {
  // Hello2 - The second implementation with getAnalysisUsage implemented.
  struct Hello2 : public FunctionPass {
    static char ID; // Pass identification, replacement for typeid
    Hello2() : FunctionPass(ID) {}
    using BasicBlockListType = SymbolTableList<BasicBlock>;
    bool runOnFunction(Function &F) override {
      ++HelloCounter;
      errs() << "now process funcName: ";
      errs().write_escaped(F.getName()) << '
';
      //we just what to show how to Traverse
      //BBsize = F.size();
      //when you just want get all instructions, you can use llvm::instructions(F)
      uint BBsize = 0;
      uint instSize = 0;
      BasicBlockListType::const_iterator bbEnd = F.end();
      for(BasicBlockListType::const_iterator bbIter=F.begin(); bbIter!=bbEnd; ++bbIter){
        BBsize += 1;
        SymbolTableList<Instruction>::const_iterator instIter = bbIter->begin();
        SymbolTableList<Instruction>::const_iterator instEnd  = bbIter->end();
        for(; instIter != instEnd; ++instIter){
          instSize ++;
          std::string opcName(instIter->getOpcodeName());
          std::map<std::string, uint>::iterator itFind =
            opCodeMap.find(opcName);
          if(itFind != opCodeMap.end() ){
            opCodeMap[opcName]++;
          }
          else{
            opCodeMap[opcName] = 1;
          }
        }
      }
      //
      errs() << "    has "<< BBsize <<" BasicBlocks "<<instSize <<" insts
";
      for(auto it : opCodeMap){
        errs() <<"   total opcode now use "<<it.first <<" "<<it.second <<"
";
      }
      return false;
    }

    // We don't modify the program, so we preserve all analyses.
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesAll();
    }
    std::map<std::string, uint> opCodeMap;
  };
}

char Hello2::ID = 0;
static RegisterPass<Hello2>
Y("hello2", "Hello World Pass (with getAnalysisUsage implemented)");

使用上一节的测试hello.c 这次需要将命令换为 ./bin/opt -load lib/LLVMHello.so -hello2 < hello.bc > /dev/null 

结果如下图：