ExtractGV.cpp revision 9ccaf53ada99c63737547c0235baeb8454b04e80 
1//===-- ExtractGV.cpp - Global Value extraction 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 pass extracts global values
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Instructions.h"
15#include "llvm/LLVMContext.h"
16#include "llvm/Module.h"
17#include "llvm/Pass.h"
18#include "llvm/Constants.h"
19#include "llvm/Transforms/IPO.h"
20#include <algorithm>
21using namespace llvm;
22
23namespace {
24  /// @brief A pass to extract specific functions and their dependencies.
25  class GVExtractorPass : public ModulePass {
26    std::vector<GlobalValue*> Named;
27    bool deleteStuff;
28    bool reLink;
29  public:
30    static char ID; // Pass identification, replacement for typeid
31
32    /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
33    /// specified function. Otherwise, it deletes as much of the module as
34    /// possible, except for the function specified.
35    ///
36    explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true,
37                             bool relinkCallees = false)
38      : ModulePass(ID), Named(GVs), deleteStuff(deleteS),
39        reLink(relinkCallees) {}
40
41    bool runOnModule(Module &M) {
42      if (Named.size() == 0) {
43        return false;  // Nothing to extract
44      }
45
46
47      if (deleteStuff)
48        return deleteGV();
49      M.setModuleInlineAsm("");
50      return isolateGV(M);
51    }
52
53    bool deleteGV() {
54      for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
55             GE = Named.end(); GI != GE; ++GI) {
56        if (Function* NamedFunc = dyn_cast<Function>(*GI)) {
57         // If we're in relinking mode, set linkage of all internal callees to
58         // external. This will allow us extract function, and then - link
59         // everything together
60         if (reLink) {
61           for (Function::iterator B = NamedFunc->begin(), BE = NamedFunc->end();
62                B != BE; ++B) {
63             for (BasicBlock::iterator I = B->begin(), E = B->end();
64                  I != E; ++I) {
65               if (CallInst* callInst = dyn_cast<CallInst>(&*I)) {
66                 Function* Callee = callInst->getCalledFunction();
67                 if (Callee && Callee->hasLocalLinkage())
68                   Callee->setLinkage(GlobalValue::ExternalLinkage);
69               }
70             }
71           }
72         }
73
74         NamedFunc->setLinkage(GlobalValue::ExternalLinkage);
75         NamedFunc->deleteBody();
76         assert(NamedFunc->isDeclaration() && "This didn't make the function external!");
77       } else {
78          if (!(*GI)->isDeclaration()) {
79            cast<GlobalVariable>(*GI)->setInitializer(0);  //clear the initializer
80            (*GI)->setLinkage(GlobalValue::ExternalLinkage);
81          }
82        }
83      }
84      return true;
85    }
86
87    bool isolateGV(Module &M) {
88      // Mark all globals internal
89      // FIXME: what should we do with private linkage?
90      for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
91        if (!I->isDeclaration()) {
92          I->setLinkage(GlobalValue::InternalLinkage);
93        }
94      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
95        if (!I->isDeclaration()) {
96          I->setLinkage(GlobalValue::InternalLinkage);
97        }
98
99      // Make sure our result is globally accessible...
100      // by putting them in the used array
101      {
102        std::vector<Constant *> AUGs;
103        const Type *SBP=
104              Type::getInt8PtrTy(M.getContext());
105        for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
106               GE = Named.end(); GI != GE; ++GI) {
107          (*GI)->setLinkage(GlobalValue::ExternalLinkage);
108          AUGs.push_back(ConstantExpr::getBitCast(*GI, SBP));
109        }
110        ArrayType *AT = ArrayType::get(SBP, AUGs.size());
111        Constant *Init = ConstantArray::get(AT, AUGs);
112        GlobalValue *gv = new GlobalVariable(M, AT, false,
113                                             GlobalValue::AppendingLinkage,
114                                             Init, "llvm.used");
115        gv->setSection("llvm.metadata");
116      }
117
118      // All of the functions may be used by global variables or the named
119      // globals.  Loop through them and create a new, external functions that
120      // can be "used", instead of ones with bodies.
121      std::vector<Function*> NewFunctions;
122
123      Function *Last = --M.end();  // Figure out where the last real fn is.
124
125      for (Module::iterator I = M.begin(); ; ++I) {
126        if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
127          Function *New = Function::Create(I->getFunctionType(),
128                                           GlobalValue::ExternalLinkage);
129          New->copyAttributesFrom(I);
130
131          // If it's not the named function, delete the body of the function
132          I->dropAllReferences();
133
134          M.getFunctionList().push_back(New);
135          NewFunctions.push_back(New);
136          New->takeName(I);
137        }
138
139        if (&*I == Last) break;  // Stop after processing the last function
140      }
141
142      // Now that we have replacements all set up, loop through the module,
143      // deleting the old functions, replacing them with the newly created
144      // functions.
145      if (!NewFunctions.empty()) {
146        unsigned FuncNum = 0;
147        Module::iterator I = M.begin();
148        do {
149          if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
150            // Make everything that uses the old function use the new dummy fn
151            I->replaceAllUsesWith(NewFunctions[FuncNum++]);
152
153            Function *Old = I;
154            ++I;  // Move the iterator to the new function
155
156            // Delete the old function!
157            M.getFunctionList().erase(Old);
158
159          } else {
160            ++I;  // Skip the function we are extracting
161          }
162        } while (&*I != NewFunctions[0]);
163      }
164
165      return true;
166    }
167  };
168
169  char GVExtractorPass::ID = 0;
170}
171
172ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
173                                         bool deleteFn, bool relinkCallees) {
174  return new GVExtractorPass(GVs, deleteFn, relinkCallees);
175}
176