ExtractGV.cpp revision e0f136d9637981bbc5096ca396e4df383c59eafe 
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 "llvm/Support/Compiler.h"
21#include <algorithm>
22using namespace llvm;
23
24namespace {
25  /// @brief A pass to extract specific functions and their dependencies.
26  class VISIBILITY_HIDDEN GVExtractorPass : public ModulePass {
27    std::vector<GlobalValue*> Named;
28    bool deleteStuff;
29    bool reLink;
30  public:
31    static char ID; // Pass identification, replacement for typeid
32
33    /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
34    /// specified function. Otherwise, it deletes as much of the module as
35    /// possible, except for the function specified.
36    ///
37    explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true,
38                             bool relinkCallees = false)
39      : ModulePass(&ID), Named(GVs), deleteStuff(deleteS),
40        reLink(relinkCallees) {}
41
42    bool runOnModule(Module &M) {
43      if (Named.size() == 0) {
44        return false;  // Nothing to extract
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= Context->getPointerTypeUnqual(Type::Int8Ty);
104        for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
105               GE = Named.end(); GI != GE; ++GI) {
106          (*GI)->setLinkage(GlobalValue::ExternalLinkage);
107          AUGs.push_back(Context->getConstantExprBitCast(*GI, SBP));
108        }
109        ArrayType *AT = Context->getArrayType(SBP, AUGs.size());
110        Constant *Init = Context->getConstantArray(AT, AUGs);
111        GlobalValue *gv = new GlobalVariable(M.getContext(), AT, false,
112                                             GlobalValue::AppendingLinkage,
113                                             Init, "llvm.used", &M);
114        gv->setSection("llvm.metadata");
115      }
116
117      // All of the functions may be used by global variables or the named
118      // globals.  Loop through them and create a new, external functions that
119      // can be "used", instead of ones with bodies.
120      std::vector<Function*> NewFunctions;
121
122      Function *Last = --M.end();  // Figure out where the last real fn is.
123
124      for (Module::iterator I = M.begin(); ; ++I) {
125        if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
126          Function *New = Function::Create(I->getFunctionType(),
127                                           GlobalValue::ExternalLinkage);
128          New->copyAttributesFrom(I);
129
130          // If it's not the named function, delete the body of the function
131          I->dropAllReferences();
132
133          M.getFunctionList().push_back(New);
134          NewFunctions.push_back(New);
135          New->takeName(I);
136        }
137
138        if (&*I == Last) break;  // Stop after processing the last function
139      }
140
141      // Now that we have replacements all set up, loop through the module,
142      // deleting the old functions, replacing them with the newly created
143      // functions.
144      if (!NewFunctions.empty()) {
145        unsigned FuncNum = 0;
146        Module::iterator I = M.begin();
147        do {
148          if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
149            // Make everything that uses the old function use the new dummy fn
150            I->replaceAllUsesWith(NewFunctions[FuncNum++]);
151
152            Function *Old = I;
153            ++I;  // Move the iterator to the new function
154
155            // Delete the old function!
156            M.getFunctionList().erase(Old);
157
158          } else {
159            ++I;  // Skip the function we are extracting
160          }
161        } while (&*I != NewFunctions[0]);
162      }
163
164      return true;
165    }
166  };
167
168  char GVExtractorPass::ID = 0;
169}
170
171ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
172                                         bool deleteFn, bool relinkCallees) {
173  return new GVExtractorPass(GVs, deleteFn, relinkCallees);
174}
175