| //===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This simple pass provides alias and mod/ref information for global values |
| // that do not have their address taken, and keeps track of whether functions |
| // read or write memory (are "pure"). For this simple (but very common) case, |
| // we can provide pretty accurate and useful information. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/Passes.h" |
| #include "llvm/Module.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/CallGraph.h" |
| #include "llvm/Support/InstIterator.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/SCCIterator.h" |
| #include <set> |
| using namespace llvm; |
| |
| namespace { |
| Statistic<> |
| NumNonAddrTakenGlobalVars("globalsmodref-aa", |
| "Number of global vars without address taken"); |
| Statistic<> |
| NumNonAddrTakenFunctions("globalsmodref-aa", |
| "Number of functions without address taken"); |
| Statistic<> |
| NumNoMemFunctions("globalsmodref-aa", |
| "Number of functions that do not access memory"); |
| Statistic<> |
| NumReadMemFunctions("globalsmodref-aa", |
| "Number of functions that only read memory"); |
| |
| /// FunctionRecord - One instance of this structure is stored for every |
| /// function in the program. Later, the entries for these functions are |
| /// removed if the function is found to call an external function (in which |
| /// case we know nothing about it. |
| struct FunctionRecord { |
| /// GlobalInfo - Maintain mod/ref info for all of the globals without |
| /// addresses taken that are read or written (transitively) by this |
| /// function. |
| std::map<GlobalValue*, unsigned> GlobalInfo; |
| |
| unsigned getInfoForGlobal(GlobalValue *GV) const { |
| std::map<GlobalValue*, unsigned>::const_iterator I = GlobalInfo.find(GV); |
| if (I != GlobalInfo.end()) |
| return I->second; |
| return 0; |
| } |
| |
| /// FunctionEffect - Capture whether or not this function reads or writes to |
| /// ANY memory. If not, we can do a lot of aggressive analysis on it. |
| unsigned FunctionEffect; |
| |
| FunctionRecord() : FunctionEffect(0) {} |
| }; |
| |
| /// GlobalsModRef - The actual analysis pass. |
| class GlobalsModRef : public ModulePass, public AliasAnalysis { |
| /// NonAddressTakenGlobals - The globals that do not have their addresses |
| /// taken. |
| std::set<GlobalValue*> NonAddressTakenGlobals; |
| |
| /// FunctionInfo - For each function, keep track of what globals are |
| /// modified or read. |
| std::map<Function*, FunctionRecord> FunctionInfo; |
| |
| public: |
| bool runOnModule(Module &M) { |
| InitializeAliasAnalysis(this); // set up super class |
| AnalyzeGlobals(M); // find non-addr taken globals |
| AnalyzeCallGraph(getAnalysis<CallGraph>(), M); // Propagate on CG |
| return false; |
| } |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AliasAnalysis::getAnalysisUsage(AU); |
| AU.addRequired<CallGraph>(); |
| AU.setPreservesAll(); // Does not transform code |
| } |
| |
| //------------------------------------------------ |
| // Implement the AliasAnalysis API |
| // |
| AliasResult alias(const Value *V1, unsigned V1Size, |
| const Value *V2, unsigned V2Size); |
| ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); |
| ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { |
| return AliasAnalysis::getModRefInfo(CS1,CS2); |
| } |
| bool hasNoModRefInfoForCalls() const { return false; } |
| |
| /// getModRefBehavior - Return the behavior of the specified function if |
| /// called from the specified call site. The call site may be null in which |
| /// case the most generic behavior of this function should be returned. |
| virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS, |
| std::vector<PointerAccessInfo> *Info) { |
| if (FunctionRecord *FR = getFunctionInfo(F)) |
| if (FR->FunctionEffect == 0) |
| return DoesNotAccessMemory; |
| else if ((FR->FunctionEffect & Mod) == 0) |
| return OnlyReadsMemory; |
| return AliasAnalysis::getModRefBehavior(F, CS, Info); |
| } |
| |
| virtual void deleteValue(Value *V); |
| virtual void copyValue(Value *From, Value *To); |
| |
| private: |
| /// getFunctionInfo - Return the function info for the function, or null if |
| /// the function calls an external function (in which case we don't have |
| /// anything useful to say about it). |
| FunctionRecord *getFunctionInfo(Function *F) { |
| std::map<Function*, FunctionRecord>::iterator I = FunctionInfo.find(F); |
| if (I != FunctionInfo.end()) |
| return &I->second; |
| return 0; |
| } |
| |
| void AnalyzeGlobals(Module &M); |
| void AnalyzeCallGraph(CallGraph &CG, Module &M); |
| void AnalyzeSCC(std::vector<CallGraphNode *> &SCC); |
| bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers, |
| std::vector<Function*> &Writers); |
| }; |
| |
| RegisterOpt<GlobalsModRef> X("globalsmodref-aa", |
| "Simple mod/ref analysis for globals"); |
| RegisterAnalysisGroup<AliasAnalysis, GlobalsModRef> Y; |
| } |
| |
| Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); } |
| |
| |
| /// AnalyzeGlobalUses - Scan through the users of all of the internal |
| /// GlobalValue's in the program. If none of them have their "Address taken" |
| /// (really, their address passed to something nontrivial), record this fact, |
| /// and record the functions that they are used directly in. |
| void GlobalsModRef::AnalyzeGlobals(Module &M) { |
| std::vector<Function*> Readers, Writers; |
| for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) |
| if (I->hasInternalLinkage()) { |
| if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) { |
| // Remember that we are tracking this global. |
| NonAddressTakenGlobals.insert(I); |
| ++NumNonAddrTakenFunctions; |
| } |
| Readers.clear(); Writers.clear(); |
| } |
| |
| for (Module::global_iterator I = M.global_begin(), E = M.global_end(); |
| I != E; ++I) |
| if (I->hasInternalLinkage()) { |
| if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) { |
| // Remember that we are tracking this global, and the mod/ref fns |
| NonAddressTakenGlobals.insert(I); |
| for (unsigned i = 0, e = Readers.size(); i != e; ++i) |
| FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref; |
| |
| if (!I->isConstant()) // No need to keep track of writers to constants |
| for (unsigned i = 0, e = Writers.size(); i != e; ++i) |
| FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod; |
| ++NumNonAddrTakenGlobalVars; |
| } |
| Readers.clear(); Writers.clear(); |
| } |
| } |
| |
| /// AnalyzeUsesOfGlobal - Look at all of the users of the specified global value |
| /// derived pointer. If this is used by anything complex (i.e., the address |
| /// escapes), return true. Also, while we are at it, keep track of those |
| /// functions that read and write to the value. |
| bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V, |
| std::vector<Function*> &Readers, |
| std::vector<Function*> &Writers) { |
| if (!isa<PointerType>(V->getType())) return true; |
| |
| for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) |
| if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { |
| Readers.push_back(LI->getParent()->getParent()); |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { |
| if (V == SI->getOperand(0)) return true; // Storing the pointer |
| Writers.push_back(SI->getParent()->getParent()); |
| } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { |
| if (AnalyzeUsesOfGlobal(GEP, Readers, Writers)) return true; |
| } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { |
| // Make sure that this is just the function being called, not that it is |
| // passing into the function. |
| for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i) |
| if (CI->getOperand(i) == V) return true; |
| } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { |
| // Make sure that this is just the function being called, not that it is |
| // passing into the function. |
| for (unsigned i = 3, e = II->getNumOperands(); i != e; ++i) |
| if (II->getOperand(i) == V) return true; |
| } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) { |
| if (CE->getOpcode() == Instruction::GetElementPtr || |
| CE->getOpcode() == Instruction::Cast) { |
| if (AnalyzeUsesOfGlobal(CE, Readers, Writers)) |
| return true; |
| } else { |
| return true; |
| } |
| } else if (GlobalValue *GV = dyn_cast<GlobalValue>(*UI)) { |
| if (AnalyzeUsesOfGlobal(GV, Readers, Writers)) return true; |
| } else { |
| return true; |
| } |
| return false; |
| } |
| |
| /// AnalyzeCallGraph - At this point, we know the functions where globals are |
| /// immediately stored to and read from. Propagate this information up the call |
| /// graph to all callers and compute the mod/ref info for all memory for each |
| /// function. |
| void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) { |
| // We do a bottom-up SCC traversal of the call graph. In other words, we |
| // visit all callees before callers (leaf-first). |
| for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG); I!=E; ++I) |
| if ((*I).size() != 1) { |
| AnalyzeSCC(*I); |
| } else if (Function *F = (*I)[0]->getFunction()) { |
| if (!F->isExternal()) { |
| // Nonexternal function. |
| AnalyzeSCC(*I); |
| } else { |
| // Otherwise external function. Handle intrinsics and other special |
| // cases here. |
| if (getAnalysis<AliasAnalysis>().doesNotAccessMemory(F)) |
| // If it does not access memory, process the function, causing us to |
| // realize it doesn't do anything (the body is empty). |
| AnalyzeSCC(*I); |
| else { |
| // Otherwise, don't process it. This will cause us to conservatively |
| // assume the worst. |
| } |
| } |
| } else { |
| // Do not process the external node, assume the worst. |
| } |
| } |
| |
| void GlobalsModRef::AnalyzeSCC(std::vector<CallGraphNode *> &SCC) { |
| assert(!SCC.empty() && "SCC with no functions?"); |
| FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()]; |
| |
| bool CallsExternal = false; |
| unsigned FunctionEffect = 0; |
| |
| // Collect the mod/ref properties due to called functions. We only compute |
| // one mod-ref set |
| for (unsigned i = 0, e = SCC.size(); i != e && !CallsExternal; ++i) |
| for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end(); |
| CI != E; ++CI) |
| if (Function *Callee = (*CI)->getFunction()) { |
| if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) { |
| // Propagate function effect up. |
| FunctionEffect |= CalleeFR->FunctionEffect; |
| |
| // Incorporate callee's effects on globals into our info. |
| for (std::map<GlobalValue*, unsigned>::iterator GI = |
| CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end(); |
| GI != E; ++GI) |
| FR.GlobalInfo[GI->first] |= GI->second; |
| |
| } else { |
| // Okay, if we can't say anything about it, maybe some other alias |
| // analysis can. |
| ModRefBehavior MRB = |
| AliasAnalysis::getModRefBehavior(Callee, CallSite()); |
| if (MRB != DoesNotAccessMemory) { |
| // FIXME: could make this more aggressive for functions that just |
| // read memory. We should just say they read all globals. |
| CallsExternal = true; |
| break; |
| } |
| } |
| } else { |
| CallsExternal = true; |
| break; |
| } |
| |
| // If this SCC calls an external function, we can't say anything about it, so |
| // remove all SCC functions from the FunctionInfo map. |
| if (CallsExternal) { |
| for (unsigned i = 0, e = SCC.size(); i != e; ++i) |
| FunctionInfo.erase(SCC[i]->getFunction()); |
| return; |
| } |
| |
| // Otherwise, unless we already know that this function mod/refs memory, scan |
| // the function bodies to see if there are any explicit loads or stores. |
| if (FunctionEffect != ModRef) { |
| for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect != ModRef;++i) |
| for (inst_iterator II = inst_begin(SCC[i]->getFunction()), |
| E = inst_end(SCC[i]->getFunction()); |
| II != E && FunctionEffect != ModRef; ++II) |
| if (isa<LoadInst>(*II)) |
| FunctionEffect |= Ref; |
| else if (isa<StoreInst>(*II)) |
| FunctionEffect |= Mod; |
| else if (isa<MallocInst>(*II) || isa<FreeInst>(*II)) |
| FunctionEffect |= ModRef; |
| } |
| |
| if ((FunctionEffect & Mod) == 0) |
| ++NumReadMemFunctions; |
| if (FunctionEffect == 0) |
| ++NumNoMemFunctions; |
| FR.FunctionEffect = FunctionEffect; |
| |
| // Finally, now that we know the full effect on this SCC, clone the |
| // information to each function in the SCC. |
| for (unsigned i = 1, e = SCC.size(); i != e; ++i) |
| FunctionInfo[SCC[i]->getFunction()] = FR; |
| } |
| |
| |
| |
| /// getUnderlyingObject - This traverses the use chain to figure out what object |
| /// the specified value points to. If the value points to, or is derived from, |
| /// a global object, return it. |
| static const GlobalValue *getUnderlyingObject(const Value *V) { |
| if (!isa<PointerType>(V->getType())) return 0; |
| |
| // If we are at some type of object... return it. |
| if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV; |
| |
| // Traverse through different addressing mechanisms... |
| if (const Instruction *I = dyn_cast<Instruction>(V)) { |
| if (isa<CastInst>(I) || isa<GetElementPtrInst>(I)) |
| return getUnderlyingObject(I->getOperand(0)); |
| } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { |
| if (CE->getOpcode() == Instruction::Cast || |
| CE->getOpcode() == Instruction::GetElementPtr) |
| return getUnderlyingObject(CE->getOperand(0)); |
| } |
| return 0; |
| } |
| |
| /// alias - If one of the pointers is to a global that we are tracking, and the |
| /// other is some random pointer, we know there cannot be an alias, because the |
| /// address of the global isn't taken. |
| AliasAnalysis::AliasResult |
| GlobalsModRef::alias(const Value *V1, unsigned V1Size, |
| const Value *V2, unsigned V2Size) { |
| GlobalValue *GV1 = const_cast<GlobalValue*>(getUnderlyingObject(V1)); |
| GlobalValue *GV2 = const_cast<GlobalValue*>(getUnderlyingObject(V2)); |
| |
| // If the global's address is taken, pretend we don't know it's a pointer to |
| // the global. |
| if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0; |
| if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0; |
| |
| if ((GV1 || GV2) && GV1 != GV2) |
| return NoAlias; |
| |
| return AliasAnalysis::alias(V1, V1Size, V2, V2Size); |
| } |
| |
| AliasAnalysis::ModRefResult |
| GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) { |
| unsigned Known = ModRef; |
| |
| // If we are asking for mod/ref info of a direct call with a pointer to a |
| // global we are tracking, return information if we have it. |
| if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P))) |
| if (GV->hasInternalLinkage()) |
| if (Function *F = CS.getCalledFunction()) |
| if (NonAddressTakenGlobals.count(GV)) |
| if (FunctionRecord *FR = getFunctionInfo(F)) |
| Known = FR->getInfoForGlobal(GV); |
| |
| if (Known == NoModRef) |
| return NoModRef; // No need to query other mod/ref analyses |
| return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, P, Size)); |
| } |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Methods to update the analysis as a result of the client transformation. |
| // |
| void GlobalsModRef::deleteValue(Value *V) { |
| if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) |
| NonAddressTakenGlobals.erase(GV); |
| } |
| |
| void GlobalsModRef::copyValue(Value *From, Value *To) { |
| } |
