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      1 //===- Hello.cpp - Example code from "Writing an LLVM Pass" ---------------===//
      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 implements two versions of the LLVM "Hello World" pass described
     11 // in docs/WritingAnLLVMPass.html
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/ADT/Statistic.h"
     16 #include "llvm/IR/Function.h"
     17 #include "llvm/Pass.h"
     18 #include "llvm/Support/raw_ostream.h"
     19 using namespace llvm;
     20 
     21 #define DEBUG_TYPE "hello"
     22 
     23 STATISTIC(HelloCounter, "Counts number of functions greeted");
     24 
     25 namespace {
     26   // Hello - The first implementation, without getAnalysisUsage.
     27   struct Hello : public FunctionPass {
     28     static char ID; // Pass identification, replacement for typeid
     29     Hello() : FunctionPass(ID) {}
     30 
     31     bool runOnFunction(Function &F) override {
     32       ++HelloCounter;
     33       errs() << "Hello: ";
     34       errs().write_escaped(F.getName()) << '\n';
     35       return false;
     36     }
     37   };
     38 }
     39 
     40 char Hello::ID = 0;
     41 static RegisterPass<Hello> X("hello", "Hello World Pass");
     42 
     43 namespace {
     44   // Hello2 - The second implementation with getAnalysisUsage implemented.
     45   struct Hello2 : public FunctionPass {
     46     static char ID; // Pass identification, replacement for typeid
     47     Hello2() : FunctionPass(ID) {}
     48 
     49     bool runOnFunction(Function &F) override {
     50       ++HelloCounter;
     51       errs() << "Hello: ";
     52       errs().write_escaped(F.getName()) << '\n';
     53       return false;
     54     }
     55 
     56     // We don't modify the program, so we preserve all analyses.
     57     void getAnalysisUsage(AnalysisUsage &AU) const override {
     58       AU.setPreservesAll();
     59     }
     60   };
     61 }
     62 
     63 char Hello2::ID = 0;
     64 static RegisterPass<Hello2>
     65 Y("hello2", "Hello World Pass (with getAnalysisUsage implemented)");
     66