GlobalsModRef.cpp revision 218893
14Srgrimes//===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===// 24Srgrimes// 34Srgrimes// The LLVM Compiler Infrastructure 44Srgrimes// 54Srgrimes// This file is distributed under the University of Illinois Open Source 64Srgrimes// License. See LICENSE.TXT for details. 74Srgrimes// 84Srgrimes//===----------------------------------------------------------------------===// 94Srgrimes// 104Srgrimes// This simple pass provides alias and mod/ref information for global values 114Srgrimes// that do not have their address taken, and keeps track of whether functions 124Srgrimes// read or write memory (are "pure"). For this simple (but very common) case, 134Srgrimes// we can provide pretty accurate and useful information. 144Srgrimes// 154Srgrimes//===----------------------------------------------------------------------===// 164Srgrimes 174Srgrimes#define DEBUG_TYPE "globalsmodref-aa" 184Srgrimes#include "llvm/Analysis/Passes.h" 194Srgrimes#include "llvm/Module.h" 204Srgrimes#include "llvm/Pass.h" 214Srgrimes#include "llvm/Instructions.h" 224Srgrimes#include "llvm/Constants.h" 234Srgrimes#include "llvm/DerivedTypes.h" 244Srgrimes#include "llvm/Analysis/AliasAnalysis.h" 254Srgrimes#include "llvm/Analysis/CallGraph.h" 264Srgrimes#include "llvm/Analysis/MemoryBuiltins.h" 274Srgrimes#include "llvm/Analysis/ValueTracking.h" 284Srgrimes#include "llvm/Support/CommandLine.h" 294Srgrimes#include "llvm/Support/InstIterator.h" 304Srgrimes#include "llvm/ADT/Statistic.h" 314Srgrimes#include "llvm/ADT/SCCIterator.h" 324Srgrimes#include <set> 334Srgrimesusing namespace llvm; 344Srgrimes 354SrgrimesSTATISTIC(NumNonAddrTakenGlobalVars, 364Srgrimes "Number of global vars without address taken"); 374SrgrimesSTATISTIC(NumNonAddrTakenFunctions,"Number of functions without address taken"); 38620SrgrimesSTATISTIC(NumNoMemFunctions, "Number of functions that do not access memory"); 3919268SjulianSTATISTIC(NumReadMemFunctions, "Number of functions that only read memory"); 404SrgrimesSTATISTIC(NumIndirectGlobalVars, "Number of indirect global objects"); 414Srgrimes 422056Swollmannamespace { 4312675Sjulian /// FunctionRecord - One instance of this structure is stored for every 4412675Sjulian /// function in the program. Later, the entries for these functions are 4512675Sjulian /// removed if the function is found to call an external function (in which 461549Srgrimes /// case we know nothing about it. 475764Sbde struct FunctionRecord { 4812675Sjulian /// GlobalInfo - Maintain mod/ref info for all of the globals without 4918951Sjulian /// addresses taken that are read or written (transitively) by this 5012701Sphk /// function. 512056Swollman std::map<const GlobalValue*, unsigned> GlobalInfo; 522056Swollman 534Srgrimes /// MayReadAnyGlobal - May read global variables, but it is not known which. 5412701Sphk bool MayReadAnyGlobal; 552056Swollman 564Srgrimes unsigned getInfoForGlobal(const GlobalValue *GV) const { 578023Sbde unsigned Effect = MayReadAnyGlobal ? AliasAnalysis::Ref : 0; 588047Sbde std::map<const GlobalValue*, unsigned>::const_iterator I = 598047Sbde GlobalInfo.find(GV); 608047Sbde if (I != GlobalInfo.end()) 615764Sbde Effect |= I->second; 6210666Sbde return Effect; 6310666Sbde } 6410666Sbde 6510666Sbde /// FunctionEffect - Capture whether or not this function reads or writes to 663728Sphk /// ANY memory. If not, we can do a lot of aggressive analysis on it. 672423Sdg unsigned FunctionEffect; 68849Sdg 693728Sphk FunctionRecord() : MayReadAnyGlobal (false), FunctionEffect(0) {} 70849Sdg }; 714Srgrimes 724Srgrimes /// GlobalsModRef - The actual analysis pass. 734Srgrimes class GlobalsModRef : public ModulePass, public AliasAnalysis { 7412675Sjulian /// NonAddressTakenGlobals - The globals that do not have their addresses 7512675Sjulian /// taken. 7612675Sjulian std::set<const GlobalValue*> NonAddressTakenGlobals; 7712675Sjulian 7812675Sjulian /// IndirectGlobals - The memory pointed to by this global is known to be 7912675Sjulian /// 'owned' by the global. 8012675Sjulian std::set<const GlobalValue*> IndirectGlobals; 8112675Sjulian 8212678Sphk /// AllocsForIndirectGlobals - If an instruction allocates memory for an 8312675Sjulian /// indirect global, this map indicates which one. 8412675Sjulian std::map<const Value*, const GlobalValue*> AllocsForIndirectGlobals; 8512675Sjulian 8612675Sjulian /// FunctionInfo - For each function, keep track of what globals are 874Srgrimes /// modified or read. 8812701Sphk std::map<const Function*, FunctionRecord> FunctionInfo; 8912701Sphk 9012701Sphk public: 9112701Sphk static char ID; 9218951Sjulian GlobalsModRef() : ModulePass(ID) { 9319268Sjulian initializeGlobalsModRefPass(*PassRegistry::getPassRegistry()); 9412701Sphk } 957680Sjoerg 967680Sjoerg bool runOnModule(Module &M) { 977680Sjoerg InitializeAliasAnalysis(this); // set up super class 987680Sjoerg AnalyzeGlobals(M); // find non-addr taken globals 994Srgrimes AnalyzeCallGraph(getAnalysis<CallGraph>(), M); // Propagate on CG 1006731Sbde return false; 1016731Sbde } 1025764Sbde 1035764Sbde virtual void getAnalysisUsage(AnalysisUsage &AU) const { 1045764Sbde AliasAnalysis::getAnalysisUsage(AU); 1057588Sjoerg AU.addRequired<CallGraph>(); 10612675Sjulian AU.setPreservesAll(); // Does not transform code 10712675Sjulian } 10812675Sjulian 1095764Sbde //------------------------------------------------ 110798Swollman // Implement the AliasAnalysis API 1114Srgrimes // 1124Srgrimes AliasResult alias(const Location &LocA, const Location &LocB); 11310665Sbde ModRefResult getModRefInfo(ImmutableCallSite CS, 1144Srgrimes const Location &Loc); 1154Srgrimes ModRefResult getModRefInfo(ImmutableCallSite CS1, 11610665Sbde ImmutableCallSite CS2) { 1174Srgrimes return AliasAnalysis::getModRefInfo(CS1, CS2); 11810665Sbde } 1194Srgrimes 1204Srgrimes /// getModRefBehavior - Return the behavior of the specified function if 1214Srgrimes /// called from the specified call site. The call site may be null in which 12210665Sbde /// case the most generic behavior of this function should be returned. 12310665Sbde ModRefBehavior getModRefBehavior(const Function *F) { 1244Srgrimes ModRefBehavior Min = UnknownModRefBehavior; 12510665Sbde 1264Srgrimes if (FunctionRecord *FR = getFunctionInfo(F)) { 12718951Sjulian if (FR->FunctionEffect == 0) 12818951Sjulian Min = DoesNotAccessMemory; 12918951Sjulian else if ((FR->FunctionEffect & Mod) == 0) 13018951Sjulian Min = OnlyReadsMemory; 13118951Sjulian } 13218951Sjulian 13318951Sjulian return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min); 13418951Sjulian } 13518951Sjulian 13618951Sjulian /// getModRefBehavior - Return the behavior of the specified function if 13718951Sjulian /// called from the specified call site. The call site may be null in which 13818951Sjulian /// case the most generic behavior of this function should be returned. 13910665Sbde ModRefBehavior getModRefBehavior(ImmutableCallSite CS) { 1404Srgrimes ModRefBehavior Min = UnknownModRefBehavior; 14110665Sbde 14210665Sbde if (const Function* F = CS.getCalledFunction()) 1434Srgrimes if (FunctionRecord *FR = getFunctionInfo(F)) { 14410665Sbde if (FR->FunctionEffect == 0) 14510665Sbde Min = DoesNotAccessMemory; 1464Srgrimes else if ((FR->FunctionEffect & Mod) == 0) 14710665Sbde Min = OnlyReadsMemory; 14810665Sbde } 14910665Sbde 15010665Sbde return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min); 15110665Sbde } 15210665Sbde 15310665Sbde virtual void deleteValue(Value *V); 15410665Sbde virtual void copyValue(Value *From, Value *To); 15510665Sbde virtual void addEscapingUse(Use &U); 15610665Sbde 15710665Sbde /// getAdjustedAnalysisPointer - This method is used when a pass implements 15810665Sbde /// an analysis interface through multiple inheritance. If needed, it 15910665Sbde /// should override this to adjust the this pointer as needed for the 16010665Sbde /// specified pass info. 16110665Sbde virtual void *getAdjustedAnalysisPointer(AnalysisID PI) { 16210665Sbde if (PI == &AliasAnalysis::ID) 16310665Sbde return (AliasAnalysis*)this; 16410665Sbde return this; 1655764Sbde } 1665764Sbde 16712813Sjulian private: 1685764Sbde /// getFunctionInfo - Return the function info for the function, or null if 1695764Sbde /// we don't have anything useful to say about it. 1705764Sbde FunctionRecord *getFunctionInfo(const Function *F) { 1715764Sbde std::map<const Function*, FunctionRecord>::iterator I = 1727588Sjoerg FunctionInfo.find(F); 17312701Sphk if (I != FunctionInfo.end()) 1744Srgrimes return &I->second; 1754Srgrimes return 0; 17612675Sjulian } 1774Srgrimes 1784Srgrimes void AnalyzeGlobals(Module &M); 1794Srgrimes void AnalyzeCallGraph(CallGraph &CG, Module &M); 1804Srgrimes bool AnalyzeUsesOfPointer(Value *V, std::vector<Function*> &Readers, 1814Srgrimes std::vector<Function*> &Writers, 1825764Sbde GlobalValue *OkayStoreDest = 0); 1835764Sbde bool AnalyzeIndirectGlobalMemory(GlobalValue *GV); 1841007Sdg }; 1854Srgrimes} 1864Srgrimes 1875764Sbdechar GlobalsModRef::ID = 0; 1885764SbdeINITIALIZE_AG_PASS_BEGIN(GlobalsModRef, AliasAnalysis, 1895764Sbde "globalsmodref-aa", "Simple mod/ref analysis for globals", 1905764Sbde false, true, false) 1915764SbdeINITIALIZE_AG_DEPENDENCY(CallGraph) 1925764SbdeINITIALIZE_AG_PASS_END(GlobalsModRef, AliasAnalysis, 1935764Sbde "globalsmodref-aa", "Simple mod/ref analysis for globals", 1945764Sbde false, true, false) 1955764Sbde 1965764SbdePass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); } 1974Srgrimes 1988876Srgrimes/// AnalyzeGlobals - Scan through the users of all of the internal 19912675Sjulian/// GlobalValue's in the program. If none of them have their "address taken" 2004Srgrimes/// (really, their address passed to something nontrivial), record this fact, 2014Srgrimes/// and record the functions that they are used directly in. 2024Srgrimesvoid GlobalsModRef::AnalyzeGlobals(Module &M) { 2034Srgrimes std::vector<Function*> Readers, Writers; 2044Srgrimes for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 2055764Sbde if (I->hasLocalLinkage()) { 2061007Sdg if (!AnalyzeUsesOfPointer(I, Readers, Writers)) { 2074Srgrimes // Remember that we are tracking this global. 2084Srgrimes NonAddressTakenGlobals.insert(I); 2095764Sbde ++NumNonAddrTakenFunctions; 2105764Sbde } 2117588Sjoerg Readers.clear(); Writers.clear(); 2125764Sbde } 2137588Sjoerg 2147588Sjoerg for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 2157588Sjoerg I != E; ++I) 2167588Sjoerg if (I->hasLocalLinkage()) { 2177588Sjoerg if (!AnalyzeUsesOfPointer(I, Readers, Writers)) { 2187588Sjoerg // Remember that we are tracking this global, and the mod/ref fns 2197588Sjoerg NonAddressTakenGlobals.insert(I); 2205764Sbde 2217588Sjoerg for (unsigned i = 0, e = Readers.size(); i != e; ++i) 2225764Sbde FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref; 2237588Sjoerg 2245764Sbde if (!I->isConstant()) // No need to keep track of writers to constants 2255764Sbde for (unsigned i = 0, e = Writers.size(); i != e; ++i) 2265764Sbde FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod; 2275764Sbde ++NumNonAddrTakenGlobalVars; 2285764Sbde 2295764Sbde // If this global holds a pointer type, see if it is an indirect global. 2304Srgrimes if (I->getType()->getElementType()->isPointerTy() && 2318876Srgrimes AnalyzeIndirectGlobalMemory(I)) 23212675Sjulian ++NumIndirectGlobalVars; 2334Srgrimes } 2344Srgrimes Readers.clear(); Writers.clear(); 2354Srgrimes } 236798Swollman} 2374Srgrimes 23818951Sjulian/// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer. 2394Srgrimes/// If this is used by anything complex (i.e., the address escapes), return 2404Srgrimes/// true. Also, while we are at it, keep track of those functions that read and 24112813Sjulian/// write to the value. 2424Srgrimes/// 2438876Srgrimes/// If OkayStoreDest is non-null, stores into this global are allowed. 24412675Sjulianbool GlobalsModRef::AnalyzeUsesOfPointer(Value *V, 2454Srgrimes std::vector<Function*> &Readers, 2464Srgrimes std::vector<Function*> &Writers, 2474Srgrimes GlobalValue *OkayStoreDest) { 248798Swollman if (!V->getType()->isPointerTy()) return true; 2494Srgrimes 25018951Sjulian for (Value::use_iterator UI = V->use_begin(), E=V->use_end(); UI != E; ++UI) { 2514Srgrimes User *U = *UI; 2521021Sdg if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 2534Srgrimes Readers.push_back(LI->getParent()->getParent()); 2544Srgrimes } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 2554Srgrimes if (V == SI->getOperand(1)) { 25612813Sjulian Writers.push_back(SI->getParent()->getParent()); 2574Srgrimes } else if (SI->getOperand(1) != OkayStoreDest) { 2588876Srgrimes return true; // Storing the pointer 25912675Sjulian } 2604Srgrimes } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 2614Srgrimes if (AnalyzeUsesOfPointer(GEP, Readers, Writers)) return true; 262798Swollman } else if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 2634Srgrimes if (AnalyzeUsesOfPointer(BCI, Readers, Writers, OkayStoreDest)) 264798Swollman return true; 2654Srgrimes } else if (isFreeCall(U)) { 2664Srgrimes Writers.push_back(cast<Instruction>(U)->getParent()->getParent()); 2674Srgrimes } else if (CallInst *CI = dyn_cast<CallInst>(U)) { 2684Srgrimes // Make sure that this is just the function being called, not that it is 26918951Sjulian // passing into the function. 2704Srgrimes for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) 2714Srgrimes if (CI->getArgOperand(i) == V) return true; 2724Srgrimes } else if (InvokeInst *II = dyn_cast<InvokeInst>(U)) { 2734Srgrimes // Make sure that this is just the function being called, not that it is 2744Srgrimes // passing into the function. 2754Srgrimes for (unsigned i = 0, e = II->getNumArgOperands(); i != e; ++i) 2764Srgrimes if (II->getArgOperand(i) == V) return true; 2774Srgrimes } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 2784Srgrimes if (CE->getOpcode() == Instruction::GetElementPtr || 2794Srgrimes CE->getOpcode() == Instruction::BitCast) { 2804Srgrimes if (AnalyzeUsesOfPointer(CE, Readers, Writers)) 2814Srgrimes return true; 2824Srgrimes } else { 28312813Sjulian return true; 2844Srgrimes } 2854Srgrimes } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(U)) { 28612675Sjulian if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 2874Srgrimes return true; // Allow comparison against null. 2884Srgrimes } else { 2894Srgrimes return true; 2904Srgrimes } 2914Srgrimes } 29218951Sjulian 2934Srgrimes return false; 2946712Spst} 2956712Spst 2966712Spst/// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable 29712813Sjulian/// which holds a pointer type. See if the global always points to non-aliased 2984Srgrimes/// heap memory: that is, all initializers of the globals are allocations, and 2994Srgrimes/// those allocations have no use other than initialization of the global. 300798Swollman/// Further, all loads out of GV must directly use the memory, not store the 3014Srgrimes/// pointer somewhere. If this is true, we consider the memory pointed to by 3024Srgrimes/// GV to be owned by GV and can disambiguate other pointers from it. 3035160Sjoergbool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) { 30418951Sjulian // Keep track of values related to the allocation of the memory, f.e. the 30519268Sjulian // value produced by the malloc call and any casts. 3065160Sjoerg std::vector<Value*> AllocRelatedValues; 3075160Sjoerg 3085160Sjoerg // Walk the user list of the global. If we find anything other than a direct 3094Srgrimes // load or store, bail out. 3104Srgrimes for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){ 3113728Sphk User *U = *I; 3123728Sphk if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 3133728Sphk // The pointer loaded from the global can only be used in simple ways: 31418951Sjulian // we allow addressing of it and loading storing to it. We do *not* allow 31518287Sbde // storing the loaded pointer somewhere else or passing to a function. 3163728Sphk std::vector<Function*> ReadersWriters; 3173728Sphk if (AnalyzeUsesOfPointer(LI, ReadersWriters, ReadersWriters)) 3183728Sphk return false; // Loaded pointer escapes. 319798Swollman // TODO: Could try some IP mod/ref of the loaded pointer. 3204Srgrimes } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 3214Srgrimes // Storing the global itself. 3224Srgrimes if (SI->getOperand(0) == GV) return false; 32318951Sjulian 3244Srgrimes // If storing the null pointer, ignore it. 3254Srgrimes if (isa<ConstantPointerNull>(SI->getOperand(0))) 3264Srgrimes continue; 3274Srgrimes 3289217Sbde // Check the value being stored. 3294Srgrimes Value *Ptr = GetUnderlyingObject(SI->getOperand(0)); 3304Srgrimes 3314Srgrimes if (isMalloc(Ptr)) { 33212517Sjulian // Okay, easy case. 33312517Sjulian } else if (CallInst *CI = dyn_cast<CallInst>(Ptr)) { 33412675Sjulian Function *F = CI->getCalledFunction(); 33512675Sjulian if (!F || !F->isDeclaration()) return false; // Too hard to analyze. 33612517Sjulian if (F->getName() != "calloc") return false; // Not calloc. 33712517Sjulian } else { 33812517Sjulian return false; // Too hard to analyze. 33912517Sjulian } 34012517Sjulian 34112517Sjulian // Analyze all uses of the allocation. If any of them are used in a 34212517Sjulian // non-simple way (e.g. stored to another global) bail out. 34312517Sjulian std::vector<Function*> ReadersWriters; 34414880Sbde if (AnalyzeUsesOfPointer(Ptr, ReadersWriters, ReadersWriters, GV)) 34514880Sbde return false; // Loaded pointer escapes. 34614880Sbde 34712517Sjulian // Remember that this allocation is related to the indirect global. 34812521Sjulian AllocRelatedValues.push_back(Ptr); 34912517Sjulian } else { 35012517Sjulian // Something complex, bail out. 35112517Sjulian return false; 35212517Sjulian } 35312517Sjulian } 354 355 // Okay, this is an indirect global. Remember all of the allocations for 356 // this global in AllocsForIndirectGlobals. 357 while (!AllocRelatedValues.empty()) { 358 AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV; 359 AllocRelatedValues.pop_back(); 360 } 361 IndirectGlobals.insert(GV); 362 return true; 363} 364 365/// AnalyzeCallGraph - At this point, we know the functions where globals are 366/// immediately stored to and read from. Propagate this information up the call 367/// graph to all callers and compute the mod/ref info for all memory for each 368/// function. 369void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) { 370 // We do a bottom-up SCC traversal of the call graph. In other words, we 371 // visit all callees before callers (leaf-first). 372 for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG); I != E; 373 ++I) { 374 std::vector<CallGraphNode *> &SCC = *I; 375 assert(!SCC.empty() && "SCC with no functions?"); 376 377 if (!SCC[0]->getFunction()) { 378 // Calls externally - can't say anything useful. Remove any existing 379 // function records (may have been created when scanning globals). 380 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 381 FunctionInfo.erase(SCC[i]->getFunction()); 382 continue; 383 } 384 385 FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()]; 386 387 bool KnowNothing = false; 388 unsigned FunctionEffect = 0; 389 390 // Collect the mod/ref properties due to called functions. We only compute 391 // one mod-ref set. 392 for (unsigned i = 0, e = SCC.size(); i != e && !KnowNothing; ++i) { 393 Function *F = SCC[i]->getFunction(); 394 if (!F) { 395 KnowNothing = true; 396 break; 397 } 398 399 if (F->isDeclaration()) { 400 // Try to get mod/ref behaviour from function attributes. 401 if (F->doesNotAccessMemory()) { 402 // Can't do better than that! 403 } else if (F->onlyReadsMemory()) { 404 FunctionEffect |= Ref; 405 if (!F->isIntrinsic()) 406 // This function might call back into the module and read a global - 407 // consider every global as possibly being read by this function. 408 FR.MayReadAnyGlobal = true; 409 } else { 410 FunctionEffect |= ModRef; 411 // Can't say anything useful unless it's an intrinsic - they don't 412 // read or write global variables of the kind considered here. 413 KnowNothing = !F->isIntrinsic(); 414 } 415 continue; 416 } 417 418 for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end(); 419 CI != E && !KnowNothing; ++CI) 420 if (Function *Callee = CI->second->getFunction()) { 421 if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) { 422 // Propagate function effect up. 423 FunctionEffect |= CalleeFR->FunctionEffect; 424 425 // Incorporate callee's effects on globals into our info. 426 for (std::map<const GlobalValue*, unsigned>::iterator GI = 427 CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end(); 428 GI != E; ++GI) 429 FR.GlobalInfo[GI->first] |= GI->second; 430 FR.MayReadAnyGlobal |= CalleeFR->MayReadAnyGlobal; 431 } else { 432 // Can't say anything about it. However, if it is inside our SCC, 433 // then nothing needs to be done. 434 CallGraphNode *CalleeNode = CG[Callee]; 435 if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end()) 436 KnowNothing = true; 437 } 438 } else { 439 KnowNothing = true; 440 } 441 } 442 443 // If we can't say anything useful about this SCC, remove all SCC functions 444 // from the FunctionInfo map. 445 if (KnowNothing) { 446 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 447 FunctionInfo.erase(SCC[i]->getFunction()); 448 continue; 449 } 450 451 // Scan the function bodies for explicit loads or stores. 452 for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect != ModRef;++i) 453 for (inst_iterator II = inst_begin(SCC[i]->getFunction()), 454 E = inst_end(SCC[i]->getFunction()); 455 II != E && FunctionEffect != ModRef; ++II) 456 if (isa<LoadInst>(*II)) { 457 FunctionEffect |= Ref; 458 if (cast<LoadInst>(*II).isVolatile()) 459 // Volatile loads may have side-effects, so mark them as writing 460 // memory (for example, a flag inside the processor). 461 FunctionEffect |= Mod; 462 } else if (isa<StoreInst>(*II)) { 463 FunctionEffect |= Mod; 464 if (cast<StoreInst>(*II).isVolatile()) 465 // Treat volatile stores as reading memory somewhere. 466 FunctionEffect |= Ref; 467 } else if (isMalloc(&cast<Instruction>(*II)) || 468 isFreeCall(&cast<Instruction>(*II))) { 469 FunctionEffect |= ModRef; 470 } 471 472 if ((FunctionEffect & Mod) == 0) 473 ++NumReadMemFunctions; 474 if (FunctionEffect == 0) 475 ++NumNoMemFunctions; 476 FR.FunctionEffect = FunctionEffect; 477 478 // Finally, now that we know the full effect on this SCC, clone the 479 // information to each function in the SCC. 480 for (unsigned i = 1, e = SCC.size(); i != e; ++i) 481 FunctionInfo[SCC[i]->getFunction()] = FR; 482 } 483} 484 485 486 487/// alias - If one of the pointers is to a global that we are tracking, and the 488/// other is some random pointer, we know there cannot be an alias, because the 489/// address of the global isn't taken. 490AliasAnalysis::AliasResult 491GlobalsModRef::alias(const Location &LocA, 492 const Location &LocB) { 493 // Get the base object these pointers point to. 494 const Value *UV1 = GetUnderlyingObject(LocA.Ptr); 495 const Value *UV2 = GetUnderlyingObject(LocB.Ptr); 496 497 // If either of the underlying values is a global, they may be non-addr-taken 498 // globals, which we can answer queries about. 499 const GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1); 500 const GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2); 501 if (GV1 || GV2) { 502 // If the global's address is taken, pretend we don't know it's a pointer to 503 // the global. 504 if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0; 505 if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0; 506 507 // If the two pointers are derived from two different non-addr-taken 508 // globals, or if one is and the other isn't, we know these can't alias. 509 if ((GV1 || GV2) && GV1 != GV2) 510 return NoAlias; 511 512 // Otherwise if they are both derived from the same addr-taken global, we 513 // can't know the two accesses don't overlap. 514 } 515 516 // These pointers may be based on the memory owned by an indirect global. If 517 // so, we may be able to handle this. First check to see if the base pointer 518 // is a direct load from an indirect global. 519 GV1 = GV2 = 0; 520 if (const LoadInst *LI = dyn_cast<LoadInst>(UV1)) 521 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0))) 522 if (IndirectGlobals.count(GV)) 523 GV1 = GV; 524 if (const LoadInst *LI = dyn_cast<LoadInst>(UV2)) 525 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0))) 526 if (IndirectGlobals.count(GV)) 527 GV2 = GV; 528 529 // These pointers may also be from an allocation for the indirect global. If 530 // so, also handle them. 531 if (AllocsForIndirectGlobals.count(UV1)) 532 GV1 = AllocsForIndirectGlobals[UV1]; 533 if (AllocsForIndirectGlobals.count(UV2)) 534 GV2 = AllocsForIndirectGlobals[UV2]; 535 536 // Now that we know whether the two pointers are related to indirect globals, 537 // use this to disambiguate the pointers. If either pointer is based on an 538 // indirect global and if they are not both based on the same indirect global, 539 // they cannot alias. 540 if ((GV1 || GV2) && GV1 != GV2) 541 return NoAlias; 542 543 return AliasAnalysis::alias(LocA, LocB); 544} 545 546AliasAnalysis::ModRefResult 547GlobalsModRef::getModRefInfo(ImmutableCallSite CS, 548 const Location &Loc) { 549 unsigned Known = ModRef; 550 551 // If we are asking for mod/ref info of a direct call with a pointer to a 552 // global we are tracking, return information if we have it. 553 if (const GlobalValue *GV = 554 dyn_cast<GlobalValue>(GetUnderlyingObject(Loc.Ptr))) 555 if (GV->hasLocalLinkage()) 556 if (const Function *F = CS.getCalledFunction()) 557 if (NonAddressTakenGlobals.count(GV)) 558 if (const FunctionRecord *FR = getFunctionInfo(F)) 559 Known = FR->getInfoForGlobal(GV); 560 561 if (Known == NoModRef) 562 return NoModRef; // No need to query other mod/ref analyses 563 return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, Loc)); 564} 565 566 567//===----------------------------------------------------------------------===// 568// Methods to update the analysis as a result of the client transformation. 569// 570void GlobalsModRef::deleteValue(Value *V) { 571 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 572 if (NonAddressTakenGlobals.erase(GV)) { 573 // This global might be an indirect global. If so, remove it and remove 574 // any AllocRelatedValues for it. 575 if (IndirectGlobals.erase(GV)) { 576 // Remove any entries in AllocsForIndirectGlobals for this global. 577 for (std::map<const Value*, const GlobalValue*>::iterator 578 I = AllocsForIndirectGlobals.begin(), 579 E = AllocsForIndirectGlobals.end(); I != E; ) { 580 if (I->second == GV) { 581 AllocsForIndirectGlobals.erase(I++); 582 } else { 583 ++I; 584 } 585 } 586 } 587 } 588 } 589 590 // Otherwise, if this is an allocation related to an indirect global, remove 591 // it. 592 AllocsForIndirectGlobals.erase(V); 593 594 AliasAnalysis::deleteValue(V); 595} 596 597void GlobalsModRef::copyValue(Value *From, Value *To) { 598 AliasAnalysis::copyValue(From, To); 599} 600 601void GlobalsModRef::addEscapingUse(Use &U) { 602 // For the purposes of this analysis, it is conservatively correct to treat 603 // a newly escaping value equivalently to a deleted one. We could perhaps 604 // be more precise by processing the new use and attempting to update our 605 // saved analysis results to accomodate it. 606 deleteValue(U); 607 608 AliasAnalysis::addEscapingUse(U); 609} 610