ExtractGV.cpp revision 0cc9058a792d86876b5ea532eb8be6842b407123 
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/Module.h"
16#include "llvm/Pass.h"
17#include "llvm/Constants.h"
18#include "llvm/Transforms/IPO.h"
19#include "llvm/Support/Compiler.h"
20#include <algorithm>
21using namespace llvm;
22
23namespace {
24  /// @brief A pass to extract specific functions and their dependencies.
25  class VISIBILITY_HIDDEN 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((intptr_t)&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      if (deleteStuff)
47        return deleteGV();
48      M.setModuleInlineAsm("");
49      return isolateGV(M);
50    }
51
52    bool deleteGV() {
53      for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
54             GE = Named.end(); GI != GE; ++GI) {
55        if (Function* NamedFunc = dyn_cast<Function>(&*GI)) {
56         // If we're in relinking mode, set linkage of all internal callees to
57         // external. This will allow us extract function, and then - link
58         // everything together
59         if (reLink) {
60           for (Function::iterator B = NamedFunc->begin(), BE = NamedFunc->end();
61                B != BE; ++B) {
62             for (BasicBlock::iterator I = B->begin(), E = B->end();
63                  I != E; ++I) {
64               if (CallInst* callInst = dyn_cast<CallInst>(&*I)) {
65                 Function* Callee = callInst->getCalledFunction();
66                 if (Callee && Callee->hasInternalLinkage())
67                   Callee->setLinkage(GlobalValue::ExternalLinkage);
68               }
69             }
70           }
71         }
72
73         NamedFunc->setLinkage(GlobalValue::ExternalLinkage);
74         NamedFunc->deleteBody();
75         assert(NamedFunc->isDeclaration() && "This didn't make the function external!");
76       } else {
77          if (!(*GI)->isDeclaration()) {
78            cast<GlobalVariable>(*GI)->setInitializer(0);  //clear the initializer
79            (*GI)->setLinkage(GlobalValue::ExternalLinkage);
80          }
81        }
82      }
83      return true;
84    }
85
86    bool isolateGV(Module &M) {
87      // Mark all globals internal
88      for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
89        if (!I->isDeclaration()) {
90          I->setLinkage(GlobalValue::InternalLinkage);
91        }
92      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
93        if (!I->isDeclaration()) {
94          I->setLinkage(GlobalValue::InternalLinkage);
95        }
96
97      // Make sure our result is globally accessible...
98      // by putting them in the used array
99      {
100        std::vector<Constant *> AUGs;
101        const Type *SBP= PointerType::getUnqual(Type::Int8Ty);
102        for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
103               GE = Named.end(); GI != GE; ++GI) {
104          (*GI)->setLinkage(GlobalValue::ExternalLinkage);
105          AUGs.push_back(ConstantExpr::getBitCast(*GI, SBP));
106        }
107        ArrayType *AT = ArrayType::get(SBP, AUGs.size());
108        Constant *Init = ConstantArray::get(AT, AUGs);
109        GlobalValue *gv = new GlobalVariable(AT, false,
110                                             GlobalValue::AppendingLinkage,
111                                             Init, "llvm.used", &M);
112        gv->setSection("llvm.metadata");
113      }
114
115      // All of the functions may be used by global variables or the named
116      // globals.  Loop through them and create a new, external functions that
117      // can be "used", instead of ones with bodies.
118      std::vector<Function*> NewFunctions;
119
120      Function *Last = --M.end();  // Figure out where the last real fn is.
121
122      for (Module::iterator I = M.begin(); ; ++I) {
123        if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
124          Function *New = Function::Create(I->getFunctionType(),
125                                           GlobalValue::ExternalLinkage);
126          New->copyAttributesFrom(I);
127
128          // If it's not the named function, delete the body of the function
129          I->dropAllReferences();
130
131          M.getFunctionList().push_back(New);
132          NewFunctions.push_back(New);
133          New->takeName(I);
134        }
135
136        if (&*I == Last) break;  // Stop after processing the last function
137      }
138
139      // Now that we have replacements all set up, loop through the module,
140      // deleting the old functions, replacing them with the newly created
141      // functions.
142      if (!NewFunctions.empty()) {
143        unsigned FuncNum = 0;
144        Module::iterator I = M.begin();
145        do {
146          if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
147            // Make everything that uses the old function use the new dummy fn
148            I->replaceAllUsesWith(NewFunctions[FuncNum++]);
149
150            Function *Old = I;
151            ++I;  // Move the iterator to the new function
152
153            // Delete the old function!
154            M.getFunctionList().erase(Old);
155
156          } else {
157            ++I;  // Skip the function we are extracting
158          }
159        } while (&*I != NewFunctions[0]);
160      }
161
162      return true;
163    }
164  };
165
166  char GVExtractorPass::ID = 0;
167}
168
169ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
170                                         bool deleteFn, bool relinkCallees) {
171  return new GVExtractorPass(GVs, deleteFn, relinkCallees);
172}
173