LLVM API Documentation

FunctionResolution.cpp

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00001 //===- FunctionResolution.cpp - Resolve declarations to implementations ---===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // Loop over the functions that are in the module and look for functions that
00011 // have the same name.  More often than not, there will be things like:
00012 //
00013 //    declare void %foo(...)
00014 //    void %foo(int, int) { ... }
00015 //
00016 // because of the way things are declared in C.  If this is the case, patch
00017 // things up.
00018 //
00019 //===----------------------------------------------------------------------===//
00020 
00021 #include "llvm/Transforms/IPO.h"
00022 #include "llvm/Module.h"
00023 #include "llvm/DerivedTypes.h"
00024 #include "llvm/Pass.h"
00025 #include "llvm/Instructions.h"
00026 #include "llvm/Constants.h"
00027 #include "llvm/Support/CallSite.h"
00028 #include "llvm/Target/TargetData.h"
00029 #include "llvm/Assembly/Writer.h"
00030 #include "llvm/ADT/Statistic.h"
00031 #include <algorithm>
00032 #include <iostream>
00033 using namespace llvm;
00034 
00035 namespace {
00036   Statistic<>NumResolved("funcresolve", "Number of varargs functions resolved");
00037   Statistic<> NumGlobals("funcresolve", "Number of global variables resolved");
00038 
00039   struct FunctionResolvingPass : public ModulePass {
00040     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00041       AU.addRequired<TargetData>();
00042     }
00043 
00044     bool runOnModule(Module &M);
00045   };
00046   RegisterOpt<FunctionResolvingPass> X("funcresolve", "Resolve Functions");
00047 }
00048 
00049 ModulePass *llvm::createFunctionResolvingPass() {
00050   return new FunctionResolvingPass();
00051 }
00052 
00053 static bool ResolveFunctions(Module &M, std::vector<GlobalValue*> &Globals,
00054                              Function *Concrete) {
00055   bool Changed = false;
00056   for (unsigned i = 0; i != Globals.size(); ++i)
00057     if (Globals[i] != Concrete) {
00058       Function *Old = cast<Function>(Globals[i]);
00059       const FunctionType *OldFT = Old->getFunctionType();
00060       const FunctionType *ConcreteFT = Concrete->getFunctionType();
00061 
00062       if (OldFT->getNumParams() > ConcreteFT->getNumParams() &&
00063           !ConcreteFT->isVarArg())
00064         if (!Old->use_empty()) {
00065           std::cerr << "WARNING: Linking function '" << Old->getName()
00066                     << "' is causing arguments to be dropped.\n";
00067           std::cerr << "WARNING: Prototype: ";
00068           WriteAsOperand(std::cerr, Old);
00069           std::cerr << " resolved to ";
00070           WriteAsOperand(std::cerr, Concrete);
00071           std::cerr << "\n";
00072         }
00073 
00074       // Check to make sure that if there are specified types, that they
00075       // match...
00076       //
00077       unsigned NumArguments = std::min(OldFT->getNumParams(),
00078                                        ConcreteFT->getNumParams());
00079 
00080       if (!Old->use_empty() && !Concrete->use_empty())
00081         for (unsigned i = 0; i < NumArguments; ++i)
00082           if (OldFT->getParamType(i) != ConcreteFT->getParamType(i))
00083             if (OldFT->getParamType(i)->getTypeID() !=
00084                 ConcreteFT->getParamType(i)->getTypeID()) {
00085               std::cerr << "WARNING: Function [" << Old->getName()
00086                         << "]: Parameter types conflict for: '";
00087               WriteTypeSymbolic(std::cerr, OldFT, &M);
00088               std::cerr << "' (in " 
00089                 << Old->getParent()->getModuleIdentifier() << ") and '";
00090               WriteTypeSymbolic(std::cerr, ConcreteFT, &M);
00091               std::cerr << "'(in " 
00092                 << Concrete->getParent()->getModuleIdentifier() << ")\n";
00093               return Changed;
00094             }
00095 
00096       // Attempt to convert all of the uses of the old function to the concrete
00097       // form of the function.  If there is a use of the fn that we don't
00098       // understand here we punt to avoid making a bad transformation.
00099       //
00100       // At this point, we know that the return values are the same for our two
00101       // functions and that the Old function has no varargs fns specified.  In
00102       // otherwords it's just <retty> (...)
00103       //
00104       if (!Old->use_empty()) {
00105         Value *Replacement = Concrete;
00106         if (Concrete->getType() != Old->getType())
00107           Replacement = ConstantExpr::getCast(Concrete, Old->getType());
00108         NumResolved += Old->getNumUses();
00109         Old->replaceAllUsesWith(Replacement);
00110       }
00111 
00112       // Since there are no uses of Old anymore, remove it from the module.
00113       M.getFunctionList().erase(Old);
00114     }
00115   return Changed;
00116 }
00117 
00118 
00119 static bool ResolveGlobalVariables(Module &M,
00120                                    std::vector<GlobalValue*> &Globals,
00121                                    GlobalVariable *Concrete) {
00122   bool Changed = false;
00123 
00124   for (unsigned i = 0; i != Globals.size(); ++i)
00125     if (Globals[i] != Concrete) {
00126       Constant *Cast = ConstantExpr::getCast(Concrete, Globals[i]->getType());
00127       Globals[i]->replaceAllUsesWith(Cast);
00128 
00129       // Since there are no uses of Old anymore, remove it from the module.
00130       M.getGlobalList().erase(cast<GlobalVariable>(Globals[i]));
00131 
00132       ++NumGlobals;
00133       Changed = true;
00134     }
00135   return Changed;
00136 }
00137 
00138 // Check to see if all of the callers of F ignore the return value.
00139 static bool CallersAllIgnoreReturnValue(Function &F) {
00140   if (F.getReturnType() == Type::VoidTy) return true;
00141   for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
00142     if (GlobalValue *GV = dyn_cast<GlobalValue>(*I)) {
00143       for (Value::use_iterator I = GV->use_begin(), E = GV->use_end();
00144            I != E; ++I) {
00145         CallSite CS = CallSite::get(*I);
00146         if (!CS.getInstruction() || !CS.getInstruction()->use_empty())
00147           return false;
00148       }
00149     } else {
00150       CallSite CS = CallSite::get(*I);
00151       if (!CS.getInstruction() || !CS.getInstruction()->use_empty())
00152         return false;
00153     }
00154   }
00155   return true;
00156 }
00157 
00158 static bool ProcessGlobalsWithSameName(Module &M, TargetData &TD,
00159                                        std::vector<GlobalValue*> &Globals) {
00160   assert(!Globals.empty() && "Globals list shouldn't be empty here!");
00161 
00162   bool isFunction = isa<Function>(Globals[0]);   // Is this group all functions?
00163   GlobalValue *Concrete = 0;  // The most concrete implementation to resolve to
00164 
00165   for (unsigned i = 0; i != Globals.size(); ) {
00166     if (isa<Function>(Globals[i]) != isFunction) {
00167       std::cerr << "WARNING: Found function and global variable with the "
00168                 << "same name: '" << Globals[i]->getName() << "'.\n";
00169       return false;                 // Don't know how to handle this, bail out!
00170     }
00171 
00172     if (isFunction) {
00173       // For functions, we look to merge functions definitions of "int (...)"
00174       // to 'int (int)' or 'int ()' or whatever else is not completely generic.
00175       //
00176       Function *F = cast<Function>(Globals[i]);
00177       if (!F->isExternal()) {
00178         if (Concrete && !Concrete->isExternal())
00179           return false;   // Found two different functions types.  Can't choose!
00180 
00181         Concrete = Globals[i];
00182       } else if (Concrete) {
00183         if (Concrete->isExternal()) // If we have multiple external symbols...
00184           if (F->getFunctionType()->getNumParams() >
00185               cast<Function>(Concrete)->getFunctionType()->getNumParams())
00186             Concrete = F;  // We are more concrete than "Concrete"!
00187 
00188       } else {
00189         Concrete = F;
00190       }
00191     } else {
00192       GlobalVariable *GV = cast<GlobalVariable>(Globals[i]);
00193       if (!GV->isExternal()) {
00194         if (Concrete) {
00195           std::cerr << "WARNING: Two global variables with external linkage"
00196                     << " exist with the same name: '" << GV->getName()
00197                     << "'!\n";
00198           return false;
00199         }
00200         Concrete = GV;
00201       }
00202     }
00203     ++i;
00204   }
00205 
00206   if (Globals.size() > 1) {         // Found a multiply defined global...
00207     // If there are no external declarations, and there is at most one
00208     // externally visible instance of the global, then there is nothing to do.
00209     //
00210     bool HasExternal = false;
00211     unsigned NumInstancesWithExternalLinkage = 0;
00212 
00213     for (unsigned i = 0, e = Globals.size(); i != e; ++i) {
00214       if (Globals[i]->isExternal())
00215         HasExternal = true;
00216       else if (!Globals[i]->hasInternalLinkage())
00217         NumInstancesWithExternalLinkage++;
00218     }
00219 
00220     if (!HasExternal && NumInstancesWithExternalLinkage <= 1)
00221       return false;  // Nothing to do?  Must have multiple internal definitions.
00222 
00223     // There are a couple of special cases we don't want to print the warning
00224     // for, check them now.
00225     bool DontPrintWarning = false;
00226     if (Concrete && Globals.size() == 2) {
00227       GlobalValue *Other = Globals[Globals[0] == Concrete];
00228       // If the non-concrete global is a function which takes (...) arguments,
00229       // and the return values match (or was never used), do not warn.
00230       if (Function *ConcreteF = dyn_cast<Function>(Concrete))
00231         if (Function *OtherF = dyn_cast<Function>(Other))
00232           if ((ConcreteF->getReturnType() == OtherF->getReturnType() ||
00233                CallersAllIgnoreReturnValue(*OtherF)) &&
00234               OtherF->getFunctionType()->isVarArg() &&
00235               OtherF->getFunctionType()->getNumParams() == 0)
00236             DontPrintWarning = true;
00237 
00238       // Otherwise, if the non-concrete global is a global array variable with a
00239       // size of 0, and the concrete global is an array with a real size, don't
00240       // warn.  This occurs due to declaring 'extern int A[];'.
00241       if (GlobalVariable *ConcreteGV = dyn_cast<GlobalVariable>(Concrete))
00242         if (GlobalVariable *OtherGV = dyn_cast<GlobalVariable>(Other)) {
00243           const Type *CTy = ConcreteGV->getType();
00244           const Type *OTy = OtherGV->getType();
00245 
00246           if (CTy->isSized())
00247             if (!OTy->isSized() || !TD.getTypeSize(OTy) ||
00248                 TD.getTypeSize(OTy) == TD.getTypeSize(CTy))
00249               DontPrintWarning = true;
00250         }
00251     }
00252 
00253     if (0 && !DontPrintWarning) {
00254       std::cerr << "WARNING: Found global types that are not compatible:\n";
00255       for (unsigned i = 0; i < Globals.size(); ++i) {
00256         std::cerr << "\t";
00257         WriteTypeSymbolic(std::cerr, Globals[i]->getType(), &M);
00258         std::cerr << " %" << Globals[i]->getName() << "\n";
00259       }
00260     }
00261 
00262     if (!Concrete)
00263       Concrete = Globals[0];
00264     else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Concrete)) {
00265       // Handle special case hack to change globals if it will make their types
00266       // happier in the long run.  The situation we do this is intentionally
00267       // extremely limited.
00268       if (GV->use_empty() && GV->hasInitializer() &&
00269           GV->getInitializer()->isNullValue()) {
00270         // Check to see if there is another (external) global with the same size
00271         // and a non-empty use-list.  If so, we will make IT be the real
00272         // implementation.
00273         unsigned TS = TD.getTypeSize(Concrete->getType()->getElementType());
00274         for (unsigned i = 0, e = Globals.size(); i != e; ++i)
00275           if (Globals[i] != Concrete && !Globals[i]->use_empty() &&
00276               isa<GlobalVariable>(Globals[i]) &&
00277               TD.getTypeSize(Globals[i]->getType()->getElementType()) == TS) {
00278             // At this point we want to replace Concrete with Globals[i].  Make
00279             // concrete external, and Globals[i] have an initializer.
00280             GlobalVariable *NGV = cast<GlobalVariable>(Globals[i]);
00281             const Type *ElTy = NGV->getType()->getElementType();
00282             NGV->setInitializer(Constant::getNullValue(ElTy));
00283             cast<GlobalVariable>(Concrete)->setInitializer(0);
00284             Concrete = NGV;
00285             break;
00286           }
00287       }
00288     }
00289 
00290     if (isFunction)
00291       return ResolveFunctions(M, Globals, cast<Function>(Concrete));
00292     else
00293       return ResolveGlobalVariables(M, Globals,
00294                                     cast<GlobalVariable>(Concrete));
00295   }
00296   return false;
00297 }
00298 
00299 bool FunctionResolvingPass::runOnModule(Module &M) {
00300   std::map<std::string, std::vector<GlobalValue*> > Globals;
00301 
00302   // Loop over the globals, adding them to the Globals map.  We use a two pass
00303   // algorithm here to avoid problems with iterators getting invalidated if we
00304   // did a one pass scheme.
00305   //
00306   bool Changed = false;
00307   for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
00308     Function *F = I++;
00309     if (F->use_empty() && F->isExternal()) {
00310       M.getFunctionList().erase(F);
00311       Changed = true;
00312     } else if (!F->hasInternalLinkage() && !F->getName().empty() &&
00313                !F->getIntrinsicID())
00314       Globals[F->getName()].push_back(F);
00315   }
00316 
00317   for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ) {
00318     GlobalVariable *GV = I++;
00319     if (GV->use_empty() && GV->isExternal()) {
00320       M.getGlobalList().erase(GV);
00321       Changed = true;
00322     } else if (!GV->hasInternalLinkage() && !GV->getName().empty())
00323       Globals[GV->getName()].push_back(GV);
00324   }
00325 
00326   TargetData &TD = getAnalysis<TargetData>();
00327 
00328   // Now we have a list of all functions with a particular name.  If there is
00329   // more than one entry in a list, merge the functions together.
00330   //
00331   for (std::map<std::string, std::vector<GlobalValue*> >::iterator
00332          I = Globals.begin(), E = Globals.end(); I != E; ++I)
00333     Changed |= ProcessGlobalsWithSameName(M, TD, I->second);
00334 
00335   // Now loop over all of the globals, checking to see if any are trivially
00336   // dead.  If so, remove them now.
00337 
00338   for (Module::iterator I = M.begin(), E = M.end(); I != E; )
00339     if (I->isExternal() && I->use_empty()) {
00340       Function *F = I;
00341       ++I;
00342       M.getFunctionList().erase(F);
00343       ++NumResolved;
00344       Changed = true;
00345     } else {
00346       ++I;
00347     }
00348 
00349   for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; )
00350     if (I->isExternal() && I->use_empty()) {
00351       GlobalVariable *GV = I;
00352       ++I;
00353       M.getGlobalList().erase(GV);
00354       ++NumGlobals;
00355       Changed = true;
00356     } else {
00357       ++I;
00358     }
00359 
00360   return Changed;
00361 }