1 //===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This simple pass provides alias and mod/ref information for global values
11 // that do not have their address taken, and keeps track of whether functions
12 // read or write memory (are "pure"). For this simple (but very common) case,
13 // we can provide pretty accurate and useful information.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/ADT/SCCIterator.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/CallGraph.h"
22 #include "llvm/Analysis/MemoryBuiltins.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/InstIterator.h"
27 #include "llvm/IR/Instructions.h"
28 #include "llvm/IR/IntrinsicInst.h"
29 #include "llvm/IR/Module.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/CommandLine.h"
36 #define DEBUG_TYPE "globalsmodref-aa"
38 STATISTIC(NumNonAddrTakenGlobalVars,
39 "Number of global vars without address taken");
40 STATISTIC(NumNonAddrTakenFunctions,"Number of functions without address taken");
41 STATISTIC(NumNoMemFunctions, "Number of functions that do not access memory");
42 STATISTIC(NumReadMemFunctions, "Number of functions that only read memory");
43 STATISTIC(NumIndirectGlobalVars, "Number of indirect global objects");
45 // An option to enable unsafe alias results from the GlobalsModRef analysis.
46 // When enabled, GlobalsModRef will provide no-alias results which in extremely
47 // rare cases may not be conservatively correct. In particular, in the face of
48 // transforms which cause assymetry between how effective GetUnderlyingObject
49 // is for two pointers, it may produce incorrect results.
51 // These unsafe results have been returned by GMR for many years without
52 // causing significant issues in the wild and so we provide a mechanism to
53 // re-enable them for users of LLVM that have a particular performance
54 // sensitivity and no known issues. The option also makes it easy to evaluate
55 // the performance impact of these results.
56 static cl::opt<bool> EnableUnsafeGlobalsModRefAliasResults(
57 "enable-unsafe-globalsmodref-alias-results", cl::init(false), cl::Hidden);
60 /// FunctionRecord - One instance of this structure is stored for every
61 /// function in the program. Later, the entries for these functions are
62 /// removed if the function is found to call an external function (in which
63 /// case we know nothing about it.
64 struct FunctionRecord {
65 /// GlobalInfo - Maintain mod/ref info for all of the globals without
66 /// addresses taken that are read or written (transitively) by this
68 std::map<const GlobalValue *, unsigned> GlobalInfo;
70 /// MayReadAnyGlobal - May read global variables, but it is not known which.
71 bool MayReadAnyGlobal;
73 unsigned getInfoForGlobal(const GlobalValue *GV) const {
74 unsigned Effect = MayReadAnyGlobal ? AliasAnalysis::Ref : 0;
75 std::map<const GlobalValue *, unsigned>::const_iterator I =
77 if (I != GlobalInfo.end())
82 /// FunctionEffect - Capture whether or not this function reads or writes to
83 /// ANY memory. If not, we can do a lot of aggressive analysis on it.
84 unsigned FunctionEffect;
86 FunctionRecord() : MayReadAnyGlobal(false), FunctionEffect(0) {}
89 /// GlobalsModRef - The actual analysis pass.
90 class GlobalsModRef : public ModulePass, public AliasAnalysis {
91 /// The globals that do not have their addresses taken.
92 std::set<const GlobalValue *> NonAddressTakenGlobals;
94 /// IndirectGlobals - The memory pointed to by this global is known to be
95 /// 'owned' by the global.
96 std::set<const GlobalValue *> IndirectGlobals;
98 /// AllocsForIndirectGlobals - If an instruction allocates memory for an
99 /// indirect global, this map indicates which one.
100 std::map<const Value *, const GlobalValue *> AllocsForIndirectGlobals;
102 /// FunctionInfo - For each function, keep track of what globals are
103 /// modified or read.
104 std::map<const Function *, FunctionRecord> FunctionInfo;
106 /// Handle to clear this analysis on deletion of values.
107 struct DeletionCallbackHandle;
109 /// List of callbacks for globals being tracked by this analysis. Note that
110 /// these objects are quite large, but we only anticipate having one per
111 /// global tracked by this analysis. There are numerous optimizations we
112 /// could perform to the memory utilization here if this becomes a problem.
113 std::list<DeletionCallbackHandle> Handles;
117 GlobalsModRef() : ModulePass(ID) {
118 initializeGlobalsModRefPass(*PassRegistry::getPassRegistry());
121 bool runOnModule(Module &M) override {
122 InitializeAliasAnalysis(this, &M.getDataLayout());
124 // Find non-addr taken globals.
128 AnalyzeCallGraph(getAnalysis<CallGraphWrapperPass>().getCallGraph(), M);
132 void getAnalysisUsage(AnalysisUsage &AU) const override {
133 AliasAnalysis::getAnalysisUsage(AU);
134 AU.addRequired<CallGraphWrapperPass>();
135 AU.setPreservesAll(); // Does not transform code
138 //------------------------------------------------
139 // Implement the AliasAnalysis API
141 AliasResult alias(const MemoryLocation &LocA,
142 const MemoryLocation &LocB) override;
143 ModRefResult getModRefInfo(ImmutableCallSite CS,
144 const MemoryLocation &Loc) override;
145 ModRefResult getModRefInfo(ImmutableCallSite CS1,
146 ImmutableCallSite CS2) override {
147 return AliasAnalysis::getModRefInfo(CS1, CS2);
150 /// getModRefBehavior - Return the behavior of the specified function if
151 /// called from the specified call site. The call site may be null in which
152 /// case the most generic behavior of this function should be returned.
153 ModRefBehavior getModRefBehavior(const Function *F) override {
154 ModRefBehavior Min = UnknownModRefBehavior;
156 if (FunctionRecord *FR = getFunctionInfo(F)) {
157 if (FR->FunctionEffect == 0)
158 Min = DoesNotAccessMemory;
159 else if ((FR->FunctionEffect & Mod) == 0)
160 Min = OnlyReadsMemory;
163 return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
166 /// getModRefBehavior - Return the behavior of the specified function if
167 /// called from the specified call site. The call site may be null in which
168 /// case the most generic behavior of this function should be returned.
169 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
170 ModRefBehavior Min = UnknownModRefBehavior;
172 if (const Function *F = CS.getCalledFunction())
173 if (FunctionRecord *FR = getFunctionInfo(F)) {
174 if (FR->FunctionEffect == 0)
175 Min = DoesNotAccessMemory;
176 else if ((FR->FunctionEffect & Mod) == 0)
177 Min = OnlyReadsMemory;
180 return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
183 /// getAdjustedAnalysisPointer - This method is used when a pass implements
184 /// an analysis interface through multiple inheritance. If needed, it
185 /// should override this to adjust the this pointer as needed for the
186 /// specified pass info.
187 void *getAdjustedAnalysisPointer(AnalysisID PI) override {
188 if (PI == &AliasAnalysis::ID)
189 return (AliasAnalysis *)this;
194 /// getFunctionInfo - Return the function info for the function, or null if
195 /// we don't have anything useful to say about it.
196 FunctionRecord *getFunctionInfo(const Function *F) {
197 std::map<const Function *, FunctionRecord>::iterator I =
198 FunctionInfo.find(F);
199 if (I != FunctionInfo.end())
204 void AnalyzeGlobals(Module &M);
205 void AnalyzeCallGraph(CallGraph &CG, Module &M);
206 bool AnalyzeUsesOfPointer(Value *V, std::vector<Function *> &Readers,
207 std::vector<Function *> &Writers,
208 GlobalValue *OkayStoreDest = nullptr);
209 bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
213 char GlobalsModRef::ID = 0;
214 INITIALIZE_AG_PASS_BEGIN(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
215 "Simple mod/ref analysis for globals", false, true,
217 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
218 INITIALIZE_AG_PASS_END(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
219 "Simple mod/ref analysis for globals", false, true,
222 Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
224 struct GlobalsModRef::DeletionCallbackHandle final : CallbackVH {
226 std::list<DeletionCallbackHandle>::iterator I;
228 DeletionCallbackHandle(GlobalsModRef &GMR, Value *V)
229 : CallbackVH(V), GMR(GMR) {}
231 void deleted() override {
232 Value *V = getValPtr();
233 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
234 if (GMR.NonAddressTakenGlobals.erase(GV)) {
235 // This global might be an indirect global. If so, remove it and remove
236 // any AllocRelatedValues for it.
237 if (GMR.IndirectGlobals.erase(GV)) {
238 // Remove any entries in AllocsForIndirectGlobals for this global.
239 for (std::map<const Value *, const GlobalValue *>::iterator
240 I = GMR.AllocsForIndirectGlobals.begin(),
241 E = GMR.AllocsForIndirectGlobals.end();
243 if (I->second == GV) {
244 GMR.AllocsForIndirectGlobals.erase(I++);
253 // If this is an allocation related to an indirect global, remove it.
254 GMR.AllocsForIndirectGlobals.erase(V);
256 // And clear out the handle.
258 GMR.Handles.erase(I);
259 // This object is now destroyed!
263 /// AnalyzeGlobals - Scan through the users of all of the internal
264 /// GlobalValue's in the program. If none of them have their "address taken"
265 /// (really, their address passed to something nontrivial), record this fact,
266 /// and record the functions that they are used directly in.
267 void GlobalsModRef::AnalyzeGlobals(Module &M) {
268 std::vector<Function *> Readers, Writers;
269 for (Function &F : M)
270 if (F.hasLocalLinkage()) {
271 if (!AnalyzeUsesOfPointer(&F, Readers, Writers)) {
272 // Remember that we are tracking this global.
273 NonAddressTakenGlobals.insert(&F);
274 Handles.emplace_front(*this, &F);
275 Handles.front().I = Handles.begin();
276 ++NumNonAddrTakenFunctions;
282 for (GlobalVariable &GV : M.globals())
283 if (GV.hasLocalLinkage()) {
284 if (!AnalyzeUsesOfPointer(&GV, Readers, Writers)) {
285 // Remember that we are tracking this global, and the mod/ref fns
286 NonAddressTakenGlobals.insert(&GV);
287 Handles.emplace_front(*this, &GV);
288 Handles.front().I = Handles.begin();
290 for (Function *Reader : Readers)
291 FunctionInfo[Reader].GlobalInfo[&GV] |= Ref;
293 if (!GV.isConstant()) // No need to keep track of writers to constants
294 for (Function *Writer : Writers)
295 FunctionInfo[Writer].GlobalInfo[&GV] |= Mod;
296 ++NumNonAddrTakenGlobalVars;
298 // If this global holds a pointer type, see if it is an indirect global.
299 if (GV.getType()->getElementType()->isPointerTy() &&
300 AnalyzeIndirectGlobalMemory(&GV))
301 ++NumIndirectGlobalVars;
308 /// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer.
309 /// If this is used by anything complex (i.e., the address escapes), return
310 /// true. Also, while we are at it, keep track of those functions that read and
311 /// write to the value.
313 /// If OkayStoreDest is non-null, stores into this global are allowed.
314 bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V,
315 std::vector<Function *> &Readers,
316 std::vector<Function *> &Writers,
317 GlobalValue *OkayStoreDest) {
318 if (!V->getType()->isPointerTy())
321 for (Use &U : V->uses()) {
322 User *I = U.getUser();
323 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
324 Readers.push_back(LI->getParent()->getParent());
325 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
326 if (V == SI->getOperand(1)) {
327 Writers.push_back(SI->getParent()->getParent());
328 } else if (SI->getOperand(1) != OkayStoreDest) {
329 return true; // Storing the pointer
331 } else if (Operator::getOpcode(I) == Instruction::GetElementPtr) {
332 if (AnalyzeUsesOfPointer(I, Readers, Writers))
334 } else if (Operator::getOpcode(I) == Instruction::BitCast) {
335 if (AnalyzeUsesOfPointer(I, Readers, Writers, OkayStoreDest))
337 } else if (auto CS = CallSite(I)) {
338 // Make sure that this is just the function being called, not that it is
339 // passing into the function.
340 if (!CS.isCallee(&U)) {
341 // Detect calls to free.
342 if (isFreeCall(I, TLI))
343 Writers.push_back(CS->getParent()->getParent());
345 return true; // Argument of an unknown call.
347 } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
348 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
349 return true; // Allow comparison against null.
358 /// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
359 /// which holds a pointer type. See if the global always points to non-aliased
360 /// heap memory: that is, all initializers of the globals are allocations, and
361 /// those allocations have no use other than initialization of the global.
362 /// Further, all loads out of GV must directly use the memory, not store the
363 /// pointer somewhere. If this is true, we consider the memory pointed to by
364 /// GV to be owned by GV and can disambiguate other pointers from it.
365 bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
366 // Keep track of values related to the allocation of the memory, f.e. the
367 // value produced by the malloc call and any casts.
368 std::vector<Value *> AllocRelatedValues;
370 // Walk the user list of the global. If we find anything other than a direct
371 // load or store, bail out.
372 for (User *U : GV->users()) {
373 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
374 // The pointer loaded from the global can only be used in simple ways:
375 // we allow addressing of it and loading storing to it. We do *not* allow
376 // storing the loaded pointer somewhere else or passing to a function.
377 std::vector<Function *> ReadersWriters;
378 if (AnalyzeUsesOfPointer(LI, ReadersWriters, ReadersWriters))
379 return false; // Loaded pointer escapes.
380 // TODO: Could try some IP mod/ref of the loaded pointer.
381 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
382 // Storing the global itself.
383 if (SI->getOperand(0) == GV)
386 // If storing the null pointer, ignore it.
387 if (isa<ConstantPointerNull>(SI->getOperand(0)))
390 // Check the value being stored.
391 Value *Ptr = GetUnderlyingObject(SI->getOperand(0),
392 GV->getParent()->getDataLayout());
394 if (!isAllocLikeFn(Ptr, TLI))
395 return false; // Too hard to analyze.
397 // Analyze all uses of the allocation. If any of them are used in a
398 // non-simple way (e.g. stored to another global) bail out.
399 std::vector<Function *> ReadersWriters;
400 if (AnalyzeUsesOfPointer(Ptr, ReadersWriters, ReadersWriters, GV))
401 return false; // Loaded pointer escapes.
403 // Remember that this allocation is related to the indirect global.
404 AllocRelatedValues.push_back(Ptr);
406 // Something complex, bail out.
411 // Okay, this is an indirect global. Remember all of the allocations for
412 // this global in AllocsForIndirectGlobals.
413 while (!AllocRelatedValues.empty()) {
414 AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV;
415 Handles.emplace_front(*this, AllocRelatedValues.back());
416 Handles.front().I = Handles.begin();
417 AllocRelatedValues.pop_back();
419 IndirectGlobals.insert(GV);
420 Handles.emplace_front(*this, GV);
421 Handles.front().I = Handles.begin();
425 /// AnalyzeCallGraph - At this point, we know the functions where globals are
426 /// immediately stored to and read from. Propagate this information up the call
427 /// graph to all callers and compute the mod/ref info for all memory for each
429 void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
430 // We do a bottom-up SCC traversal of the call graph. In other words, we
431 // visit all callees before callers (leaf-first).
432 for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
433 const std::vector<CallGraphNode *> &SCC = *I;
434 assert(!SCC.empty() && "SCC with no functions?");
436 if (!SCC[0]->getFunction()) {
437 // Calls externally - can't say anything useful. Remove any existing
438 // function records (may have been created when scanning globals).
439 for (auto *Node : SCC)
440 FunctionInfo.erase(Node->getFunction());
444 FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()];
446 bool KnowNothing = false;
447 unsigned FunctionEffect = 0;
449 // Collect the mod/ref properties due to called functions. We only compute
451 for (unsigned i = 0, e = SCC.size(); i != e && !KnowNothing; ++i) {
452 Function *F = SCC[i]->getFunction();
458 if (F->isDeclaration()) {
459 // Try to get mod/ref behaviour from function attributes.
460 if (F->doesNotAccessMemory()) {
461 // Can't do better than that!
462 } else if (F->onlyReadsMemory()) {
463 FunctionEffect |= Ref;
464 if (!F->isIntrinsic())
465 // This function might call back into the module and read a global -
466 // consider every global as possibly being read by this function.
467 FR.MayReadAnyGlobal = true;
469 FunctionEffect |= ModRef;
470 // Can't say anything useful unless it's an intrinsic - they don't
471 // read or write global variables of the kind considered here.
472 KnowNothing = !F->isIntrinsic();
477 for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
478 CI != E && !KnowNothing; ++CI)
479 if (Function *Callee = CI->second->getFunction()) {
480 if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) {
481 // Propagate function effect up.
482 FunctionEffect |= CalleeFR->FunctionEffect;
484 // Incorporate callee's effects on globals into our info.
485 for (const auto &G : CalleeFR->GlobalInfo)
486 FR.GlobalInfo[G.first] |= G.second;
487 FR.MayReadAnyGlobal |= CalleeFR->MayReadAnyGlobal;
489 // Can't say anything about it. However, if it is inside our SCC,
490 // then nothing needs to be done.
491 CallGraphNode *CalleeNode = CG[Callee];
492 if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end())
500 // If we can't say anything useful about this SCC, remove all SCC functions
501 // from the FunctionInfo map.
503 for (auto *Node : SCC)
504 FunctionInfo.erase(Node->getFunction());
508 // Scan the function bodies for explicit loads or stores.
509 for (auto *Node : SCC) {
510 if (FunctionEffect == ModRef)
511 break; // The mod/ref lattice saturates here.
512 for (Instruction &I : inst_range(Node->getFunction())) {
513 if (FunctionEffect == ModRef)
514 break; // The mod/ref lattice saturates here.
516 // We handle calls specially because the graph-relevant aspects are
518 if (auto CS = CallSite(&I)) {
519 if (isAllocationFn(&I, TLI) || isFreeCall(&I, TLI)) {
520 // FIXME: It is completely unclear why this is necessary and not
521 // handled by the above graph code.
522 FunctionEffect |= ModRef;
523 } else if (Function *Callee = CS.getCalledFunction()) {
524 // The callgraph doesn't include intrinsic calls.
525 if (Callee->isIntrinsic()) {
526 ModRefBehavior Behaviour =
527 AliasAnalysis::getModRefBehavior(Callee);
528 FunctionEffect |= (Behaviour & ModRef);
534 // All non-call instructions we use the primary predicates for whether
535 // thay read or write memory.
536 if (I.mayReadFromMemory())
537 FunctionEffect |= Ref;
538 if (I.mayWriteToMemory())
539 FunctionEffect |= Mod;
543 if ((FunctionEffect & Mod) == 0)
544 ++NumReadMemFunctions;
545 if (FunctionEffect == 0)
547 FR.FunctionEffect = FunctionEffect;
549 // Finally, now that we know the full effect on this SCC, clone the
550 // information to each function in the SCC.
551 for (unsigned i = 1, e = SCC.size(); i != e; ++i)
552 FunctionInfo[SCC[i]->getFunction()] = FR;
556 /// alias - If one of the pointers is to a global that we are tracking, and the
557 /// other is some random pointer, we know there cannot be an alias, because the
558 /// address of the global isn't taken.
559 AliasResult GlobalsModRef::alias(const MemoryLocation &LocA,
560 const MemoryLocation &LocB) {
561 // Get the base object these pointers point to.
562 const Value *UV1 = GetUnderlyingObject(LocA.Ptr, *DL);
563 const Value *UV2 = GetUnderlyingObject(LocB.Ptr, *DL);
565 // If either of the underlying values is a global, they may be non-addr-taken
566 // globals, which we can answer queries about.
567 const GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1);
568 const GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2);
570 // If the global's address is taken, pretend we don't know it's a pointer to
572 if (GV1 && !NonAddressTakenGlobals.count(GV1))
574 if (GV2 && !NonAddressTakenGlobals.count(GV2))
577 // If the two pointers are derived from two different non-addr-taken
578 // globals we know these can't alias.
579 if (GV1 && GV2 && GV1 != GV2)
582 // If one is and the other isn't, it isn't strictly safe but we can fake
583 // this result if necessary for performance. This does not appear to be
584 // a common problem in practice.
585 if (EnableUnsafeGlobalsModRefAliasResults)
586 if ((GV1 || GV2) && GV1 != GV2)
589 // Otherwise if they are both derived from the same addr-taken global, we
590 // can't know the two accesses don't overlap.
593 // These pointers may be based on the memory owned by an indirect global. If
594 // so, we may be able to handle this. First check to see if the base pointer
595 // is a direct load from an indirect global.
597 if (const LoadInst *LI = dyn_cast<LoadInst>(UV1))
598 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
599 if (IndirectGlobals.count(GV))
601 if (const LoadInst *LI = dyn_cast<LoadInst>(UV2))
602 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
603 if (IndirectGlobals.count(GV))
606 // These pointers may also be from an allocation for the indirect global. If
607 // so, also handle them.
608 if (AllocsForIndirectGlobals.count(UV1))
609 GV1 = AllocsForIndirectGlobals[UV1];
610 if (AllocsForIndirectGlobals.count(UV2))
611 GV2 = AllocsForIndirectGlobals[UV2];
613 // Now that we know whether the two pointers are related to indirect globals,
614 // use this to disambiguate the pointers. If the pointers are based on
615 // different indirect globals they cannot alias.
616 if (GV1 && GV2 && GV1 != GV2)
619 // If one is based on an indirect global and the other isn't, it isn't
620 // strictly safe but we can fake this result if necessary for performance.
621 // This does not appear to be a common problem in practice.
622 if (EnableUnsafeGlobalsModRefAliasResults)
623 if ((GV1 || GV2) && GV1 != GV2)
626 return AliasAnalysis::alias(LocA, LocB);
629 AliasAnalysis::ModRefResult
630 GlobalsModRef::getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc) {
631 unsigned Known = ModRef;
633 // If we are asking for mod/ref info of a direct call with a pointer to a
634 // global we are tracking, return information if we have it.
635 const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout();
636 if (const GlobalValue *GV =
637 dyn_cast<GlobalValue>(GetUnderlyingObject(Loc.Ptr, DL)))
638 if (GV->hasLocalLinkage())
639 if (const Function *F = CS.getCalledFunction())
640 if (NonAddressTakenGlobals.count(GV))
641 if (const FunctionRecord *FR = getFunctionInfo(F))
642 Known = FR->getInfoForGlobal(GV);
644 if (Known == NoModRef)
645 return NoModRef; // No need to query other mod/ref analyses
646 return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, Loc));