ExtractGV.cpp revision 02b48c3be2112c64d8fc9cf5419c9c8d4ec30b71 
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
48      if (deleteStuff)
49        return deleteGV();
50      M.setModuleInlineAsm("");
51      return isolateGV(M);
52    }
53
54    bool deleteGV() {
55      for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
56             GE = Named.end(); GI != GE; ++GI) {
57        if (Function* NamedFunc = dyn_cast<Function>(*GI)) {
58         // If we're in relinking mode, set linkage of all internal callees to
59         // external. This will allow us extract function, and then - link
60         // everything together
61         if (reLink) {
62           for (Function::iterator B = NamedFunc->begin(), BE = NamedFunc->end();
63                B != BE; ++B) {
64             for (BasicBlock::iterator I = B->begin(), E = B->end();
65                  I != E; ++I) {
66               if (CallInst* callInst = dyn_cast<CallInst>(&*I)) {
67                 Function* Callee = callInst->getCalledFunction();
68                 if (Callee && Callee->hasLocalLinkage())
69                   Callee->setLinkage(GlobalValue::ExternalLinkage);
70               }
71             }
72           }
73         }
74
75         NamedFunc->setLinkage(GlobalValue::ExternalLinkage);
76         NamedFunc->deleteBody();
77         assert(NamedFunc->isDeclaration() && "This didn't make the function external!");
78       } else {
79          if (!(*GI)->isDeclaration()) {
80            cast<GlobalVariable>(*GI)->setInitializer(0);  //clear the initializer
81            (*GI)->setLinkage(GlobalValue::ExternalLinkage);
82          }
83        }
84      }
85      return true;
86    }
87
88    bool isolateGV(Module &M) {
89      LLVMContext &Context = M.getContext();
90
91      // Mark all globals internal
92      // FIXME: what should we do with private linkage?
93      for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
94        if (!I->isDeclaration()) {
95          I->setLinkage(GlobalValue::InternalLinkage);
96        }
97      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
98        if (!I->isDeclaration()) {
99          I->setLinkage(GlobalValue::InternalLinkage);
100        }
101
102      // Make sure our result is globally accessible...
103      // by putting them in the used array
104      {
105        std::vector<Constant *> AUGs;
106        const Type *SBP= Context.getPointerTypeUnqual(Type::Int8Ty);
107        for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
108               GE = Named.end(); GI != GE; ++GI) {
109          (*GI)->setLinkage(GlobalValue::ExternalLinkage);
110          AUGs.push_back(ConstantExpr::getBitCast(*GI, SBP));
111        }
112        ArrayType *AT = Context.getArrayType(SBP, AUGs.size());
113        Constant *Init = ConstantArray::get(AT, AUGs);
114        GlobalValue *gv = new GlobalVariable(M, AT, false,
115                                             GlobalValue::AppendingLinkage,
116                                             Init, "llvm.used");
117        gv->setSection("llvm.metadata");
118      }
119
120      // All of the functions may be used by global variables or the named
121      // globals.  Loop through them and create a new, external functions that
122      // can be "used", instead of ones with bodies.
123      std::vector<Function*> NewFunctions;
124
125      Function *Last = --M.end();  // Figure out where the last real fn is.
126
127      for (Module::iterator I = M.begin(); ; ++I) {
128        if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
129          Function *New = Function::Create(I->getFunctionType(),
130                                           GlobalValue::ExternalLinkage);
131          New->copyAttributesFrom(I);
132
133          // If it's not the named function, delete the body of the function
134          I->dropAllReferences();
135
136          M.getFunctionList().push_back(New);
137          NewFunctions.push_back(New);
138          New->takeName(I);
139        }
140
141        if (&*I == Last) break;  // Stop after processing the last function
142      }
143
144      // Now that we have replacements all set up, loop through the module,
145      // deleting the old functions, replacing them with the newly created
146      // functions.
147      if (!NewFunctions.empty()) {
148        unsigned FuncNum = 0;
149        Module::iterator I = M.begin();
150        do {
151          if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
152            // Make everything that uses the old function use the new dummy fn
153            I->replaceAllUsesWith(NewFunctions[FuncNum++]);
154
155            Function *Old = I;
156            ++I;  // Move the iterator to the new function
157
158            // Delete the old function!
159            M.getFunctionList().erase(Old);
160
161          } else {
162            ++I;  // Skip the function we are extracting
163          }
164        } while (&*I != NewFunctions[0]);
165      }
166
167      return true;
168    }
169  };
170
171  char GVExtractorPass::ID = 0;
172}
173
174ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
175                                         bool deleteFn, bool relinkCallees) {
176  return new GVExtractorPass(GVs, deleteFn, relinkCallees);
177}
178