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/SmallPtrSet.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/CallGraph.h"
23 #include "llvm/Analysis/MemoryBuiltins.h"
24 #include "llvm/Analysis/ValueTracking.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/InstIterator.h"
28 #include "llvm/IR/Instructions.h"
29 #include "llvm/IR/IntrinsicInst.h"
30 #include "llvm/IR/Module.h"
31 #include "llvm/Pass.h"
32 #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 /// The mod/ref information collected for a particular function.
62 /// We collect information about mod/ref behavior of a function here, both in
63 /// general and as pertains to specific globals. We only have this detailed
64 /// information when we know *something* useful about the behavior. If we
65 /// saturate to fully general mod/ref, we remove the info for the function.
68 FunctionInfo() : MayReadAnyGlobal(false), MRI(MRI_NoModRef) {}
70 /// Returns the \c ModRefInfo info for this function.
71 ModRefInfo getModRefInfo() const { return MRI; }
73 /// Adds new \c ModRefInfo for this function to its state.
74 void addModRefInfo(ModRefInfo NewMRI) { MRI = ModRefInfo(MRI | NewMRI); }
76 /// Returns whether this function may read any global variable, and we don't
77 /// know which global.
78 bool mayReadAnyGlobal() const { return MayReadAnyGlobal; }
80 /// Sets this function as potentially reading from any global.
81 void setMayReadAnyGlobal() { MayReadAnyGlobal = true; }
83 /// Returns the \c ModRefInfo info for this function w.r.t. a particular
84 /// global, which may be more precise than the general information above.
85 ModRefInfo getModRefInfoForGlobal(const GlobalValue &GV) const {
86 ModRefInfo GlobalMRI = MayReadAnyGlobal ? MRI_Ref : MRI_NoModRef;
87 auto I = GlobalInfo.find(&GV);
88 if (I != GlobalInfo.end())
89 GlobalMRI = ModRefInfo(GlobalMRI | I->second);
93 /// Access the entire map of mod/ref info for specific globals.
94 const std::map<const GlobalValue *, ModRefInfo> &getGlobalModRefInfo() const {
98 void addModRefInfoForGlobal(const GlobalValue &GV, ModRefInfo NewMRI) {
99 auto &GlobalMRI = GlobalInfo[&GV];
100 GlobalMRI = ModRefInfo(GlobalMRI | NewMRI);
104 /// Maintain mod/ref info for all of the globals without addresses taken that
105 /// are read or written (transitively) by this function.
106 std::map<const GlobalValue *, ModRefInfo> GlobalInfo;
108 /// Flag indicating this function read global variables, but it is not known
110 bool MayReadAnyGlobal;
112 /// Captures whether or not this function reads or writes to ANY memory. If
113 /// not, we can do a lot of aggressive analysis on it.
117 /// GlobalsModRef - The actual analysis pass.
118 class GlobalsModRef : public ModulePass, public AliasAnalysis {
119 /// The globals that do not have their addresses taken.
120 SmallPtrSet<const GlobalValue *, 8> NonAddressTakenGlobals;
122 /// IndirectGlobals - The memory pointed to by this global is known to be
123 /// 'owned' by the global.
124 SmallPtrSet<const GlobalValue *, 8> IndirectGlobals;
126 /// AllocsForIndirectGlobals - If an instruction allocates memory for an
127 /// indirect global, this map indicates which one.
128 DenseMap<const Value *, const GlobalValue *> AllocsForIndirectGlobals;
130 /// For each function, keep track of what globals are modified or read.
131 DenseMap<const Function *, FunctionInfo> FunctionInfos;
133 /// Handle to clear this analysis on deletion of values.
134 struct DeletionCallbackHandle final : CallbackVH {
136 std::list<DeletionCallbackHandle>::iterator I;
138 DeletionCallbackHandle(GlobalsModRef &GMR, Value *V)
139 : CallbackVH(V), GMR(GMR) {}
141 void deleted() override {
142 Value *V = getValPtr();
143 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
144 if (GMR.NonAddressTakenGlobals.erase(GV)) {
145 // This global might be an indirect global. If so, remove it and
147 // any AllocRelatedValues for it.
148 if (GMR.IndirectGlobals.erase(GV)) {
149 // Remove any entries in AllocsForIndirectGlobals for this global.
150 for (auto I = GMR.AllocsForIndirectGlobals.begin(),
151 E = GMR.AllocsForIndirectGlobals.end();
154 GMR.AllocsForIndirectGlobals.erase(I);
159 // If this is an allocation related to an indirect global, remove it.
160 GMR.AllocsForIndirectGlobals.erase(V);
162 // And clear out the handle.
164 GMR.Handles.erase(I);
165 // This object is now destroyed!
169 /// List of callbacks for globals being tracked by this analysis. Note that
170 /// these objects are quite large, but we only anticipate having one per
171 /// global tracked by this analysis. There are numerous optimizations we
172 /// could perform to the memory utilization here if this becomes a problem.
173 std::list<DeletionCallbackHandle> Handles;
177 GlobalsModRef() : ModulePass(ID) {
178 initializeGlobalsModRefPass(*PassRegistry::getPassRegistry());
181 bool runOnModule(Module &M) override {
182 InitializeAliasAnalysis(this, &M.getDataLayout());
184 // Find non-addr taken globals.
188 AnalyzeCallGraph(getAnalysis<CallGraphWrapperPass>().getCallGraph(), M);
192 void getAnalysisUsage(AnalysisUsage &AU) const override {
193 AliasAnalysis::getAnalysisUsage(AU);
194 AU.addRequired<CallGraphWrapperPass>();
195 AU.setPreservesAll(); // Does not transform code
198 /// getAdjustedAnalysisPointer - This method is used when a pass implements
199 /// an analysis interface through multiple inheritance. If needed, it
200 /// should override this to adjust the this pointer as needed for the
201 /// specified pass info.
202 void *getAdjustedAnalysisPointer(AnalysisID PI) override {
203 if (PI == &AliasAnalysis::ID)
204 return (AliasAnalysis *)this;
208 //------------------------------------------------
209 // Implement the AliasAnalysis API
211 AliasResult alias(const MemoryLocation &LocA,
212 const MemoryLocation &LocB) override;
213 ModRefInfo getModRefInfo(ImmutableCallSite CS,
214 const MemoryLocation &Loc) override;
215 ModRefInfo getModRefInfo(ImmutableCallSite CS1,
216 ImmutableCallSite CS2) override {
217 return AliasAnalysis::getModRefInfo(CS1, CS2);
220 /// getModRefBehavior - Return the behavior of the specified function if
221 /// called from the specified call site. The call site may be null in which
222 /// case the most generic behavior of this function should be returned.
223 FunctionModRefBehavior getModRefBehavior(const Function *F) override {
224 FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
226 if (FunctionInfo *FI = getFunctionInfo(F)) {
227 if (FI->getModRefInfo() == MRI_NoModRef)
228 Min = FMRB_DoesNotAccessMemory;
229 else if ((FI->getModRefInfo() & MRI_Mod) == 0)
230 Min = FMRB_OnlyReadsMemory;
233 return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
236 /// getModRefBehavior - Return the behavior of the specified function if
237 /// called from the specified call site. The call site may be null in which
238 /// case the most generic behavior of this function should be returned.
239 FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
240 FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
242 if (const Function *F = CS.getCalledFunction())
243 if (FunctionInfo *FI = getFunctionInfo(F)) {
244 if (FI->getModRefInfo() == MRI_NoModRef)
245 Min = FMRB_DoesNotAccessMemory;
246 else if ((FI->getModRefInfo() & MRI_Mod) == 0)
247 Min = FMRB_OnlyReadsMemory;
250 return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
254 /// Returns the function info for the function, or null if we don't have
255 /// anything useful to say about it.
256 FunctionInfo *getFunctionInfo(const Function *F) {
257 auto I = FunctionInfos.find(F);
258 if (I != FunctionInfos.end())
263 void AnalyzeGlobals(Module &M);
264 void AnalyzeCallGraph(CallGraph &CG, Module &M);
265 bool AnalyzeUsesOfPointer(Value *V,
266 SmallPtrSetImpl<Function *> *Readers = nullptr,
267 SmallPtrSetImpl<Function *> *Writers = nullptr,
268 GlobalValue *OkayStoreDest = nullptr);
269 bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
273 char GlobalsModRef::ID = 0;
274 INITIALIZE_AG_PASS_BEGIN(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
275 "Simple mod/ref analysis for globals", false, true,
277 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
278 INITIALIZE_AG_PASS_END(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
279 "Simple mod/ref analysis for globals", false, true,
282 Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
284 /// AnalyzeGlobals - Scan through the users of all of the internal
285 /// GlobalValue's in the program. If none of them have their "address taken"
286 /// (really, their address passed to something nontrivial), record this fact,
287 /// and record the functions that they are used directly in.
288 void GlobalsModRef::AnalyzeGlobals(Module &M) {
289 for (Function &F : M)
290 if (F.hasLocalLinkage())
291 if (!AnalyzeUsesOfPointer(&F)) {
292 // Remember that we are tracking this global.
293 NonAddressTakenGlobals.insert(&F);
294 Handles.emplace_front(*this, &F);
295 Handles.front().I = Handles.begin();
296 ++NumNonAddrTakenFunctions;
299 SmallPtrSet<Function *, 64> Readers, Writers;
300 for (GlobalVariable &GV : M.globals())
301 if (GV.hasLocalLinkage()) {
302 if (!AnalyzeUsesOfPointer(&GV, &Readers,
303 GV.isConstant() ? nullptr : &Writers)) {
304 // Remember that we are tracking this global, and the mod/ref fns
305 NonAddressTakenGlobals.insert(&GV);
306 Handles.emplace_front(*this, &GV);
307 Handles.front().I = Handles.begin();
309 for (Function *Reader : Readers)
310 FunctionInfos[Reader].addModRefInfoForGlobal(GV, MRI_Ref);
312 if (!GV.isConstant()) // No need to keep track of writers to constants
313 for (Function *Writer : Writers)
314 FunctionInfos[Writer].addModRefInfoForGlobal(GV, MRI_Mod);
315 ++NumNonAddrTakenGlobalVars;
317 // If this global holds a pointer type, see if it is an indirect global.
318 if (GV.getType()->getElementType()->isPointerTy() &&
319 AnalyzeIndirectGlobalMemory(&GV))
320 ++NumIndirectGlobalVars;
327 /// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer.
328 /// If this is used by anything complex (i.e., the address escapes), return
329 /// true. Also, while we are at it, keep track of those functions that read and
330 /// write to the value.
332 /// If OkayStoreDest is non-null, stores into this global are allowed.
333 bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V,
334 SmallPtrSetImpl<Function *> *Readers,
335 SmallPtrSetImpl<Function *> *Writers,
336 GlobalValue *OkayStoreDest) {
337 if (!V->getType()->isPointerTy())
340 for (Use &U : V->uses()) {
341 User *I = U.getUser();
342 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
344 Readers->insert(LI->getParent()->getParent());
345 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
346 if (V == SI->getOperand(1)) {
348 Writers->insert(SI->getParent()->getParent());
349 } else if (SI->getOperand(1) != OkayStoreDest) {
350 return true; // Storing the pointer
352 } else if (Operator::getOpcode(I) == Instruction::GetElementPtr) {
353 if (AnalyzeUsesOfPointer(I, Readers, Writers))
355 } else if (Operator::getOpcode(I) == Instruction::BitCast) {
356 if (AnalyzeUsesOfPointer(I, Readers, Writers, OkayStoreDest))
358 } else if (auto CS = CallSite(I)) {
359 // Make sure that this is just the function being called, not that it is
360 // passing into the function.
361 if (!CS.isCallee(&U)) {
362 // Detect calls to free.
363 if (isFreeCall(I, TLI)) {
365 Writers->insert(CS->getParent()->getParent());
367 return true; // Argument of an unknown call.
370 } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
371 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
372 return true; // Allow comparison against null.
381 /// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
382 /// which holds a pointer type. See if the global always points to non-aliased
383 /// heap memory: that is, all initializers of the globals are allocations, and
384 /// those allocations have no use other than initialization of the global.
385 /// Further, all loads out of GV must directly use the memory, not store the
386 /// pointer somewhere. If this is true, we consider the memory pointed to by
387 /// GV to be owned by GV and can disambiguate other pointers from it.
388 bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
389 // Keep track of values related to the allocation of the memory, f.e. the
390 // value produced by the malloc call and any casts.
391 std::vector<Value *> AllocRelatedValues;
393 // Walk the user list of the global. If we find anything other than a direct
394 // load or store, bail out.
395 for (User *U : GV->users()) {
396 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
397 // The pointer loaded from the global can only be used in simple ways:
398 // we allow addressing of it and loading storing to it. We do *not* allow
399 // storing the loaded pointer somewhere else or passing to a function.
400 if (AnalyzeUsesOfPointer(LI))
401 return false; // Loaded pointer escapes.
402 // TODO: Could try some IP mod/ref of the loaded pointer.
403 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
404 // Storing the global itself.
405 if (SI->getOperand(0) == GV)
408 // If storing the null pointer, ignore it.
409 if (isa<ConstantPointerNull>(SI->getOperand(0)))
412 // Check the value being stored.
413 Value *Ptr = GetUnderlyingObject(SI->getOperand(0),
414 GV->getParent()->getDataLayout());
416 if (!isAllocLikeFn(Ptr, TLI))
417 return false; // Too hard to analyze.
419 // Analyze all uses of the allocation. If any of them are used in a
420 // non-simple way (e.g. stored to another global) bail out.
421 if (AnalyzeUsesOfPointer(Ptr, /*Readers*/ nullptr, /*Writers*/ nullptr,
423 return false; // Loaded pointer escapes.
425 // Remember that this allocation is related to the indirect global.
426 AllocRelatedValues.push_back(Ptr);
428 // Something complex, bail out.
433 // Okay, this is an indirect global. Remember all of the allocations for
434 // this global in AllocsForIndirectGlobals.
435 while (!AllocRelatedValues.empty()) {
436 AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV;
437 Handles.emplace_front(*this, AllocRelatedValues.back());
438 Handles.front().I = Handles.begin();
439 AllocRelatedValues.pop_back();
441 IndirectGlobals.insert(GV);
442 Handles.emplace_front(*this, GV);
443 Handles.front().I = Handles.begin();
447 /// AnalyzeCallGraph - At this point, we know the functions where globals are
448 /// immediately stored to and read from. Propagate this information up the call
449 /// graph to all callers and compute the mod/ref info for all memory for each
451 void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
452 // We do a bottom-up SCC traversal of the call graph. In other words, we
453 // visit all callees before callers (leaf-first).
454 for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
455 const std::vector<CallGraphNode *> &SCC = *I;
456 assert(!SCC.empty() && "SCC with no functions?");
458 if (!SCC[0]->getFunction()) {
459 // Calls externally - can't say anything useful. Remove any existing
460 // function records (may have been created when scanning globals).
461 for (auto *Node : SCC)
462 FunctionInfos.erase(Node->getFunction());
466 FunctionInfo &FI = FunctionInfos[SCC[0]->getFunction()];
468 bool KnowNothing = false;
469 unsigned FunctionMRI = 0;
471 // Collect the mod/ref properties due to called functions. We only compute
473 for (unsigned i = 0, e = SCC.size(); i != e && !KnowNothing; ++i) {
474 Function *F = SCC[i]->getFunction();
480 if (F->isDeclaration()) {
481 // Try to get mod/ref behaviour from function attributes.
482 if (F->doesNotAccessMemory()) {
483 // Can't do better than that!
484 } else if (F->onlyReadsMemory()) {
485 FunctionMRI |= MRI_Ref;
486 if (!F->isIntrinsic())
487 // This function might call back into the module and read a global -
488 // consider every global as possibly being read by this function.
489 FI.setMayReadAnyGlobal();
491 FunctionMRI |= MRI_ModRef;
492 // Can't say anything useful unless it's an intrinsic - they don't
493 // read or write global variables of the kind considered here.
494 KnowNothing = !F->isIntrinsic();
499 for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
500 CI != E && !KnowNothing; ++CI)
501 if (Function *Callee = CI->second->getFunction()) {
502 if (FunctionInfo *CalleeFI = getFunctionInfo(Callee)) {
503 // Propagate function effect up.
504 FunctionMRI |= CalleeFI->getModRefInfo();
506 // Incorporate callee's effects on globals into our info.
507 for (const auto &G : CalleeFI->getGlobalModRefInfo())
508 FI.addModRefInfoForGlobal(*G.first, G.second);
510 if (CalleeFI->mayReadAnyGlobal())
511 FI.setMayReadAnyGlobal();
513 // Can't say anything about it. However, if it is inside our SCC,
514 // then nothing needs to be done.
515 CallGraphNode *CalleeNode = CG[Callee];
516 if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end())
524 // If we can't say anything useful about this SCC, remove all SCC functions
525 // from the FunctionInfos map.
527 for (auto *Node : SCC)
528 FunctionInfos.erase(Node->getFunction());
532 // Scan the function bodies for explicit loads or stores.
533 for (auto *Node : SCC) {
534 if (FunctionMRI == MRI_ModRef)
535 break; // The mod/ref lattice saturates here.
536 for (Instruction &I : inst_range(Node->getFunction())) {
537 if (FunctionMRI == MRI_ModRef)
538 break; // The mod/ref lattice saturates here.
540 // We handle calls specially because the graph-relevant aspects are
542 if (auto CS = CallSite(&I)) {
543 if (isAllocationFn(&I, TLI) || isFreeCall(&I, TLI)) {
544 // FIXME: It is completely unclear why this is necessary and not
545 // handled by the above graph code.
546 FunctionMRI |= MRI_ModRef;
547 } else if (Function *Callee = CS.getCalledFunction()) {
548 // The callgraph doesn't include intrinsic calls.
549 if (Callee->isIntrinsic()) {
550 FunctionModRefBehavior Behaviour =
551 AliasAnalysis::getModRefBehavior(Callee);
552 FunctionMRI |= (Behaviour & MRI_ModRef);
558 // All non-call instructions we use the primary predicates for whether
559 // thay read or write memory.
560 if (I.mayReadFromMemory())
561 FunctionMRI |= MRI_Ref;
562 if (I.mayWriteToMemory())
563 FunctionMRI |= MRI_Mod;
567 if ((FunctionMRI & MRI_Mod) == 0)
568 ++NumReadMemFunctions;
569 if (FunctionMRI == MRI_NoModRef)
571 FI.addModRefInfo(ModRefInfo(FunctionMRI));
573 // Finally, now that we know the full effect on this SCC, clone the
574 // information to each function in the SCC.
575 for (unsigned i = 1, e = SCC.size(); i != e; ++i)
576 FunctionInfos[SCC[i]->getFunction()] = FI;
580 /// alias - If one of the pointers is to a global that we are tracking, and the
581 /// other is some random pointer, we know there cannot be an alias, because the
582 /// address of the global isn't taken.
583 AliasResult GlobalsModRef::alias(const MemoryLocation &LocA,
584 const MemoryLocation &LocB) {
585 // Get the base object these pointers point to.
586 const Value *UV1 = GetUnderlyingObject(LocA.Ptr, *DL);
587 const Value *UV2 = GetUnderlyingObject(LocB.Ptr, *DL);
589 // If either of the underlying values is a global, they may be non-addr-taken
590 // globals, which we can answer queries about.
591 const GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1);
592 const GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2);
594 // If the global's address is taken, pretend we don't know it's a pointer to
596 if (GV1 && !NonAddressTakenGlobals.count(GV1))
598 if (GV2 && !NonAddressTakenGlobals.count(GV2))
601 // If the two pointers are derived from two different non-addr-taken
602 // globals we know these can't alias.
603 if (GV1 && GV2 && GV1 != GV2)
606 // If one is and the other isn't, it isn't strictly safe but we can fake
607 // this result if necessary for performance. This does not appear to be
608 // a common problem in practice.
609 if (EnableUnsafeGlobalsModRefAliasResults)
610 if ((GV1 || GV2) && GV1 != GV2)
613 // Otherwise if they are both derived from the same addr-taken global, we
614 // can't know the two accesses don't overlap.
617 // These pointers may be based on the memory owned by an indirect global. If
618 // so, we may be able to handle this. First check to see if the base pointer
619 // is a direct load from an indirect global.
621 if (const LoadInst *LI = dyn_cast<LoadInst>(UV1))
622 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
623 if (IndirectGlobals.count(GV))
625 if (const LoadInst *LI = dyn_cast<LoadInst>(UV2))
626 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
627 if (IndirectGlobals.count(GV))
630 // These pointers may also be from an allocation for the indirect global. If
631 // so, also handle them.
633 GV1 = AllocsForIndirectGlobals.lookup(UV1);
635 GV2 = AllocsForIndirectGlobals.lookup(UV2);
637 // Now that we know whether the two pointers are related to indirect globals,
638 // use this to disambiguate the pointers. If the pointers are based on
639 // different indirect globals they cannot alias.
640 if (GV1 && GV2 && GV1 != GV2)
643 // If one is based on an indirect global and the other isn't, it isn't
644 // strictly safe but we can fake this result if necessary for performance.
645 // This does not appear to be a common problem in practice.
646 if (EnableUnsafeGlobalsModRefAliasResults)
647 if ((GV1 || GV2) && GV1 != GV2)
650 return AliasAnalysis::alias(LocA, LocB);
653 ModRefInfo GlobalsModRef::getModRefInfo(ImmutableCallSite CS,
654 const MemoryLocation &Loc) {
655 unsigned Known = MRI_ModRef;
657 // If we are asking for mod/ref info of a direct call with a pointer to a
658 // global we are tracking, return information if we have it.
659 const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout();
660 if (const GlobalValue *GV =
661 dyn_cast<GlobalValue>(GetUnderlyingObject(Loc.Ptr, DL)))
662 if (GV->hasLocalLinkage())
663 if (const Function *F = CS.getCalledFunction())
664 if (NonAddressTakenGlobals.count(GV))
665 if (const FunctionInfo *FI = getFunctionInfo(F))
666 Known = FI->getModRefInfoForGlobal(*GV);
668 if (Known == MRI_NoModRef)
669 return MRI_NoModRef; // No need to query other mod/ref analyses
670 return ModRefInfo(Known & AliasAnalysis::getModRefInfo(CS, Loc));