1 //===- FunctionAttrs.cpp - Pass which marks functions attributes ----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements a simple interprocedural pass which walks the
11 // call-graph, looking for functions which do not access or only read
12 // non-local memory, and marking them readnone/readonly.  It does the
13 // same with function arguments independently, marking them readonly/
14 // readnone/nocapture.  Finally, well-known library call declarations
15 // are marked with all attributes that are consistent with the
16 // function's standard definition. This pass is implemented as a
17 // bottom-up traversal of the call-graph.
18 //
19 //===----------------------------------------------------------------------===//
20 
21 #include "llvm/Transforms/IPO.h"
22 #include "llvm/ADT/SCCIterator.h"
23 #include "llvm/ADT/SetVector.h"
24 #include "llvm/ADT/SmallSet.h"
25 #include "llvm/ADT/Statistic.h"
26 #include "llvm/Analysis/AliasAnalysis.h"
27 #include "llvm/Analysis/CallGraph.h"
28 #include "llvm/Analysis/CallGraphSCCPass.h"
29 #include "llvm/Analysis/CaptureTracking.h"
30 #include "llvm/IR/GlobalVariable.h"
31 #include "llvm/IR/InstIterator.h"
32 #include "llvm/IR/IntrinsicInst.h"
33 #include "llvm/IR/LLVMContext.h"
34 #include "llvm/Target/TargetLibraryInfo.h"
35 using namespace llvm;
36 
37 #define DEBUG_TYPE "functionattrs"
38 
39 STATISTIC(NumReadNone, "Number of functions marked readnone");
40 STATISTIC(NumReadOnly, "Number of functions marked readonly");
41 STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
42 STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");
43 STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
44 STATISTIC(NumNoAlias, "Number of function returns marked noalias");
45 STATISTIC(NumAnnotated, "Number of attributes added to library functions");
46 
47 namespace {
48   struct FunctionAttrs : public CallGraphSCCPass {
49     static char ID; // Pass identification, replacement for typeid
50     FunctionAttrs() : CallGraphSCCPass(ID), AA(nullptr) {
51       initializeFunctionAttrsPass(*PassRegistry::getPassRegistry());
52     }
53 
54     // runOnSCC - Analyze the SCC, performing the transformation if possible.
55     bool runOnSCC(CallGraphSCC &SCC) override;
56 
57     // AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
58     bool AddReadAttrs(const CallGraphSCC &SCC);
59 
60     // AddArgumentAttrs - Deduce nocapture attributes for the SCC.
61     bool AddArgumentAttrs(const CallGraphSCC &SCC);
62 
63     // IsFunctionMallocLike - Does this function allocate new memory?
64     bool IsFunctionMallocLike(Function *F,
65                               SmallPtrSet<Function*, 8> &) const;
66 
67     // AddNoAliasAttrs - Deduce noalias attributes for the SCC.
68     bool AddNoAliasAttrs(const CallGraphSCC &SCC);
69 
70     // Utility methods used by inferPrototypeAttributes to add attributes
71     // and maintain annotation statistics.
72 
73     void setDoesNotAccessMemory(Function &F) {
74       if (!F.doesNotAccessMemory()) {
75         F.setDoesNotAccessMemory();
76         ++NumAnnotated;
77       }
78     }
79 
80     void setOnlyReadsMemory(Function &F) {
81       if (!F.onlyReadsMemory()) {
82         F.setOnlyReadsMemory();
83         ++NumAnnotated;
84       }
85     }
86 
87     void setDoesNotThrow(Function &F) {
88       if (!F.doesNotThrow()) {
89         F.setDoesNotThrow();
90         ++NumAnnotated;
91       }
92     }
93 
94     void setDoesNotCapture(Function &F, unsigned n) {
95       if (!F.doesNotCapture(n)) {
96         F.setDoesNotCapture(n);
97         ++NumAnnotated;
98       }
99     }
100 
101     void setOnlyReadsMemory(Function &F, unsigned n) {
102       if (!F.onlyReadsMemory(n)) {
103         F.setOnlyReadsMemory(n);
104         ++NumAnnotated;
105       }
106     }
107 
108     void setDoesNotAlias(Function &F, unsigned n) {
109       if (!F.doesNotAlias(n)) {
110         F.setDoesNotAlias(n);
111         ++NumAnnotated;
112       }
113     }
114 
115     // inferPrototypeAttributes - Analyze the name and prototype of the
116     // given function and set any applicable attributes.  Returns true
117     // if any attributes were set and false otherwise.
118     bool inferPrototypeAttributes(Function &F);
119 
120     // annotateLibraryCalls - Adds attributes to well-known standard library
121     // call declarations.
122     bool annotateLibraryCalls(const CallGraphSCC &SCC);
123 
124     void getAnalysisUsage(AnalysisUsage &AU) const override {
125       AU.setPreservesCFG();
126       AU.addRequired<AliasAnalysis>();
127       AU.addRequired<TargetLibraryInfo>();
128       CallGraphSCCPass::getAnalysisUsage(AU);
129     }
130 
131   private:
132     AliasAnalysis *AA;
133     TargetLibraryInfo *TLI;
134   };
135 }
136 
137 char FunctionAttrs::ID = 0;
138 INITIALIZE_PASS_BEGIN(FunctionAttrs, "functionattrs",
139                 "Deduce function attributes", false, false)
140 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
141 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
142 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
143 INITIALIZE_PASS_END(FunctionAttrs, "functionattrs",
144                 "Deduce function attributes", false, false)
145 
146 Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
147 
148 
149 /// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
150 bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
151   SmallPtrSet<Function*, 8> SCCNodes;
152 
153   // Fill SCCNodes with the elements of the SCC.  Used for quickly
154   // looking up whether a given CallGraphNode is in this SCC.
155   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
156     SCCNodes.insert((*I)->getFunction());
157 
158   // Check if any of the functions in the SCC read or write memory.  If they
159   // write memory then they can't be marked readnone or readonly.
160   bool ReadsMemory = false;
161   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
162     Function *F = (*I)->getFunction();
163 
164     if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
165       // External node or node we don't want to optimize - assume it may write
166       // memory and give up.
167       return false;
168 
169     AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(F);
170     if (MRB == AliasAnalysis::DoesNotAccessMemory)
171       // Already perfect!
172       continue;
173 
174     // Definitions with weak linkage may be overridden at linktime with
175     // something that writes memory, so treat them like declarations.
176     if (F->isDeclaration() || F->mayBeOverridden()) {
177       if (!AliasAnalysis::onlyReadsMemory(MRB))
178         // May write memory.  Just give up.
179         return false;
180 
181       ReadsMemory = true;
182       continue;
183     }
184 
185     // Scan the function body for instructions that may read or write memory.
186     for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
187       Instruction *I = &*II;
188 
189       // Some instructions can be ignored even if they read or write memory.
190       // Detect these now, skipping to the next instruction if one is found.
191       CallSite CS(cast<Value>(I));
192       if (CS) {
193         // Ignore calls to functions in the same SCC.
194         if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
195           continue;
196         AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(CS);
197         // If the call doesn't access arbitrary memory, we may be able to
198         // figure out something.
199         if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
200           // If the call does access argument pointees, check each argument.
201           if (AliasAnalysis::doesAccessArgPointees(MRB))
202             // Check whether all pointer arguments point to local memory, and
203             // ignore calls that only access local memory.
204             for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
205                  CI != CE; ++CI) {
206               Value *Arg = *CI;
207               if (Arg->getType()->isPointerTy()) {
208                 AAMDNodes AAInfo;
209                 I->getAAMetadata(AAInfo);
210 
211                 AliasAnalysis::Location Loc(Arg,
212                                             AliasAnalysis::UnknownSize, AAInfo);
213                 if (!AA->pointsToConstantMemory(Loc, /*OrLocal=*/true)) {
214                   if (MRB & AliasAnalysis::Mod)
215                     // Writes non-local memory.  Give up.
216                     return false;
217                   if (MRB & AliasAnalysis::Ref)
218                     // Ok, it reads non-local memory.
219                     ReadsMemory = true;
220                 }
221               }
222             }
223           continue;
224         }
225         // The call could access any memory. If that includes writes, give up.
226         if (MRB & AliasAnalysis::Mod)
227           return false;
228         // If it reads, note it.
229         if (MRB & AliasAnalysis::Ref)
230           ReadsMemory = true;
231         continue;
232       } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
233         // Ignore non-volatile loads from local memory. (Atomic is okay here.)
234         if (!LI->isVolatile()) {
235           AliasAnalysis::Location Loc = AA->getLocation(LI);
236           if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
237             continue;
238         }
239       } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
240         // Ignore non-volatile stores to local memory. (Atomic is okay here.)
241         if (!SI->isVolatile()) {
242           AliasAnalysis::Location Loc = AA->getLocation(SI);
243           if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
244             continue;
245         }
246       } else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
247         // Ignore vaargs on local memory.
248         AliasAnalysis::Location Loc = AA->getLocation(VI);
249         if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
250           continue;
251       }
252 
253       // Any remaining instructions need to be taken seriously!  Check if they
254       // read or write memory.
255       if (I->mayWriteToMemory())
256         // Writes memory.  Just give up.
257         return false;
258 
259       // If this instruction may read memory, remember that.
260       ReadsMemory |= I->mayReadFromMemory();
261     }
262   }
263 
264   // Success!  Functions in this SCC do not access memory, or only read memory.
265   // Give them the appropriate attribute.
266   bool MadeChange = false;
267   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
268     Function *F = (*I)->getFunction();
269 
270     if (F->doesNotAccessMemory())
271       // Already perfect!
272       continue;
273 
274     if (F->onlyReadsMemory() && ReadsMemory)
275       // No change.
276       continue;
277 
278     MadeChange = true;
279 
280     // Clear out any existing attributes.
281     AttrBuilder B;
282     B.addAttribute(Attribute::ReadOnly)
283       .addAttribute(Attribute::ReadNone);
284     F->removeAttributes(AttributeSet::FunctionIndex,
285                         AttributeSet::get(F->getContext(),
286                                           AttributeSet::FunctionIndex, B));
287 
288     // Add in the new attribute.
289     F->addAttribute(AttributeSet::FunctionIndex,
290                     ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
291 
292     if (ReadsMemory)
293       ++NumReadOnly;
294     else
295       ++NumReadNone;
296   }
297 
298   return MadeChange;
299 }
300 
301 namespace {
302   // For a given pointer Argument, this retains a list of Arguments of functions
303   // in the same SCC that the pointer data flows into. We use this to build an
304   // SCC of the arguments.
305   struct ArgumentGraphNode {
306     Argument *Definition;
307     SmallVector<ArgumentGraphNode*, 4> Uses;
308   };
309 
310   class ArgumentGraph {
311     // We store pointers to ArgumentGraphNode objects, so it's important that
312     // that they not move around upon insert.
313     typedef std::map<Argument*, ArgumentGraphNode> ArgumentMapTy;
314 
315     ArgumentMapTy ArgumentMap;
316 
317     // There is no root node for the argument graph, in fact:
318     //   void f(int *x, int *y) { if (...) f(x, y); }
319     // is an example where the graph is disconnected. The SCCIterator requires a
320     // single entry point, so we maintain a fake ("synthetic") root node that
321     // uses every node. Because the graph is directed and nothing points into
322     // the root, it will not participate in any SCCs (except for its own).
323     ArgumentGraphNode SyntheticRoot;
324 
325   public:
326     ArgumentGraph() { SyntheticRoot.Definition = nullptr; }
327 
328     typedef SmallVectorImpl<ArgumentGraphNode*>::iterator iterator;
329 
330     iterator begin() { return SyntheticRoot.Uses.begin(); }
331     iterator end() { return SyntheticRoot.Uses.end(); }
332     ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
333 
334     ArgumentGraphNode *operator[](Argument *A) {
335       ArgumentGraphNode &Node = ArgumentMap[A];
336       Node.Definition = A;
337       SyntheticRoot.Uses.push_back(&Node);
338       return &Node;
339     }
340   };
341 
342   // This tracker checks whether callees are in the SCC, and if so it does not
343   // consider that a capture, instead adding it to the "Uses" list and
344   // continuing with the analysis.
345   struct ArgumentUsesTracker : public CaptureTracker {
346     ArgumentUsesTracker(const SmallPtrSet<Function*, 8> &SCCNodes)
347       : Captured(false), SCCNodes(SCCNodes) {}
348 
349     void tooManyUses() override { Captured = true; }
350 
351     bool captured(const Use *U) override {
352       CallSite CS(U->getUser());
353       if (!CS.getInstruction()) { Captured = true; return true; }
354 
355       Function *F = CS.getCalledFunction();
356       if (!F || !SCCNodes.count(F)) { Captured = true; return true; }
357 
358       bool Found = false;
359       Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
360       for (CallSite::arg_iterator PI = CS.arg_begin(), PE = CS.arg_end();
361            PI != PE; ++PI, ++AI) {
362         if (AI == AE) {
363           assert(F->isVarArg() && "More params than args in non-varargs call");
364           Captured = true;
365           return true;
366         }
367         if (PI == U) {
368           Uses.push_back(AI);
369           Found = true;
370           break;
371         }
372       }
373       assert(Found && "Capturing call-site captured nothing?");
374       (void)Found;
375       return false;
376     }
377 
378     bool Captured;  // True only if certainly captured (used outside our SCC).
379     SmallVector<Argument*, 4> Uses;  // Uses within our SCC.
380 
381     const SmallPtrSet<Function*, 8> &SCCNodes;
382   };
383 }
384 
385 namespace llvm {
386   template<> struct GraphTraits<ArgumentGraphNode*> {
387     typedef ArgumentGraphNode NodeType;
388     typedef SmallVectorImpl<ArgumentGraphNode*>::iterator ChildIteratorType;
389 
390     static inline NodeType *getEntryNode(NodeType *A) { return A; }
391     static inline ChildIteratorType child_begin(NodeType *N) {
392       return N->Uses.begin();
393     }
394     static inline ChildIteratorType child_end(NodeType *N) {
395       return N->Uses.end();
396     }
397   };
398   template<> struct GraphTraits<ArgumentGraph*>
399     : public GraphTraits<ArgumentGraphNode*> {
400     static NodeType *getEntryNode(ArgumentGraph *AG) {
401       return AG->getEntryNode();
402     }
403     static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
404       return AG->begin();
405     }
406     static ChildIteratorType nodes_end(ArgumentGraph *AG) {
407       return AG->end();
408     }
409   };
410 }
411 
412 // Returns Attribute::None, Attribute::ReadOnly or Attribute::ReadNone.
413 static Attribute::AttrKind
414 determinePointerReadAttrs(Argument *A,
415                           const SmallPtrSet<Argument*, 8> &SCCNodes) {
416 
417   SmallVector<Use*, 32> Worklist;
418   SmallSet<Use*, 32> Visited;
419   int Count = 0;
420 
421   // inalloca arguments are always clobbered by the call.
422   if (A->hasInAllocaAttr())
423     return Attribute::None;
424 
425   bool IsRead = false;
426   // We don't need to track IsWritten. If A is written to, return immediately.
427 
428   for (Use &U : A->uses()) {
429     if (Count++ >= 20)
430       return Attribute::None;
431 
432     Visited.insert(&U);
433     Worklist.push_back(&U);
434   }
435 
436   while (!Worklist.empty()) {
437     Use *U = Worklist.pop_back_val();
438     Instruction *I = cast<Instruction>(U->getUser());
439     Value *V = U->get();
440 
441     switch (I->getOpcode()) {
442     case Instruction::BitCast:
443     case Instruction::GetElementPtr:
444     case Instruction::PHI:
445     case Instruction::Select:
446     case Instruction::AddrSpaceCast:
447       // The original value is not read/written via this if the new value isn't.
448       for (Use &UU : I->uses())
449         if (Visited.insert(&UU))
450           Worklist.push_back(&UU);
451       break;
452 
453     case Instruction::Call:
454     case Instruction::Invoke: {
455       bool Captures = true;
456 
457       if (I->getType()->isVoidTy())
458         Captures = false;
459 
460       auto AddUsersToWorklistIfCapturing = [&] {
461         if (Captures)
462           for (Use &UU : I->uses())
463             if (Visited.insert(&UU))
464               Worklist.push_back(&UU);
465       };
466 
467       CallSite CS(I);
468       if (CS.doesNotAccessMemory()) {
469         AddUsersToWorklistIfCapturing();
470         continue;
471       }
472 
473       Function *F = CS.getCalledFunction();
474       if (!F) {
475         if (CS.onlyReadsMemory()) {
476           IsRead = true;
477           AddUsersToWorklistIfCapturing();
478           continue;
479         }
480         return Attribute::None;
481       }
482 
483       Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
484       CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
485       for (CallSite::arg_iterator A = B; A != E; ++A, ++AI) {
486         if (A->get() == V) {
487           if (AI == AE) {
488             assert(F->isVarArg() &&
489                    "More params than args in non-varargs call.");
490             return Attribute::None;
491           }
492           Captures &= !CS.doesNotCapture(A - B);
493           if (SCCNodes.count(AI))
494             continue;
495           if (!CS.onlyReadsMemory() && !CS.onlyReadsMemory(A - B))
496             return Attribute::None;
497           if (!CS.doesNotAccessMemory(A - B))
498             IsRead = true;
499         }
500       }
501       AddUsersToWorklistIfCapturing();
502       break;
503     }
504 
505     case Instruction::Load:
506       IsRead = true;
507       break;
508 
509     case Instruction::ICmp:
510     case Instruction::Ret:
511       break;
512 
513     default:
514       return Attribute::None;
515     }
516   }
517 
518   return IsRead ? Attribute::ReadOnly : Attribute::ReadNone;
519 }
520 
521 /// AddArgumentAttrs - Deduce nocapture attributes for the SCC.
522 bool FunctionAttrs::AddArgumentAttrs(const CallGraphSCC &SCC) {
523   bool Changed = false;
524 
525   SmallPtrSet<Function*, 8> SCCNodes;
526 
527   // Fill SCCNodes with the elements of the SCC.  Used for quickly
528   // looking up whether a given CallGraphNode is in this SCC.
529   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
530     Function *F = (*I)->getFunction();
531     if (F && !F->isDeclaration() && !F->mayBeOverridden() &&
532         !F->hasFnAttribute(Attribute::OptimizeNone))
533       SCCNodes.insert(F);
534   }
535 
536   ArgumentGraph AG;
537 
538   AttrBuilder B;
539   B.addAttribute(Attribute::NoCapture);
540 
541   // Check each function in turn, determining which pointer arguments are not
542   // captured.
543   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
544     Function *F = (*I)->getFunction();
545 
546     if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
547       // External node or function we're trying not to optimize - only a problem
548       // for arguments that we pass to it.
549       continue;
550 
551     // Definitions with weak linkage may be overridden at linktime with
552     // something that captures pointers, so treat them like declarations.
553     if (F->isDeclaration() || F->mayBeOverridden())
554       continue;
555 
556     // Functions that are readonly (or readnone) and nounwind and don't return
557     // a value can't capture arguments. Don't analyze them.
558     if (F->onlyReadsMemory() && F->doesNotThrow() &&
559         F->getReturnType()->isVoidTy()) {
560       for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end();
561            A != E; ++A) {
562         if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
563           A->addAttr(AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
564           ++NumNoCapture;
565           Changed = true;
566         }
567       }
568       continue;
569     }
570 
571     for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end();
572          A != E; ++A) {
573       if (!A->getType()->isPointerTy()) continue;
574       bool HasNonLocalUses = false;
575       if (!A->hasNoCaptureAttr()) {
576         ArgumentUsesTracker Tracker(SCCNodes);
577         PointerMayBeCaptured(A, &Tracker);
578         if (!Tracker.Captured) {
579           if (Tracker.Uses.empty()) {
580             // If it's trivially not captured, mark it nocapture now.
581             A->addAttr(AttributeSet::get(F->getContext(), A->getArgNo()+1, B));
582             ++NumNoCapture;
583             Changed = true;
584           } else {
585             // If it's not trivially captured and not trivially not captured,
586             // then it must be calling into another function in our SCC. Save
587             // its particulars for Argument-SCC analysis later.
588             ArgumentGraphNode *Node = AG[A];
589             for (SmallVectorImpl<Argument*>::iterator UI = Tracker.Uses.begin(),
590                      UE = Tracker.Uses.end(); UI != UE; ++UI) {
591               Node->Uses.push_back(AG[*UI]);
592               if (*UI != A)
593                 HasNonLocalUses = true;
594             }
595           }
596         }
597         // Otherwise, it's captured. Don't bother doing SCC analysis on it.
598       }
599       if (!HasNonLocalUses && !A->onlyReadsMemory()) {
600         // Can we determine that it's readonly/readnone without doing an SCC?
601         // Note that we don't allow any calls at all here, or else our result
602         // will be dependent on the iteration order through the functions in the
603         // SCC.
604         SmallPtrSet<Argument*, 8> Self;
605         Self.insert(A);
606         Attribute::AttrKind R = determinePointerReadAttrs(A, Self);
607         if (R != Attribute::None) {
608           AttrBuilder B;
609           B.addAttribute(R);
610           A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
611           Changed = true;
612           R == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
613         }
614       }
615     }
616   }
617 
618   // The graph we've collected is partial because we stopped scanning for
619   // argument uses once we solved the argument trivially. These partial nodes
620   // show up as ArgumentGraphNode objects with an empty Uses list, and for
621   // these nodes the final decision about whether they capture has already been
622   // made.  If the definition doesn't have a 'nocapture' attribute by now, it
623   // captures.
624 
625   for (scc_iterator<ArgumentGraph*> I = scc_begin(&AG); !I.isAtEnd(); ++I) {
626     const std::vector<ArgumentGraphNode *> &ArgumentSCC = *I;
627     if (ArgumentSCC.size() == 1) {
628       if (!ArgumentSCC[0]->Definition) continue;  // synthetic root node
629 
630       // eg. "void f(int* x) { if (...) f(x); }"
631       if (ArgumentSCC[0]->Uses.size() == 1 &&
632           ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
633         Argument *A = ArgumentSCC[0]->Definition;
634         A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
635         ++NumNoCapture;
636         Changed = true;
637       }
638       continue;
639     }
640 
641     bool SCCCaptured = false;
642     for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
643          I != E && !SCCCaptured; ++I) {
644       ArgumentGraphNode *Node = *I;
645       if (Node->Uses.empty()) {
646         if (!Node->Definition->hasNoCaptureAttr())
647           SCCCaptured = true;
648       }
649     }
650     if (SCCCaptured) continue;
651 
652     SmallPtrSet<Argument*, 8> ArgumentSCCNodes;
653     // Fill ArgumentSCCNodes with the elements of the ArgumentSCC.  Used for
654     // quickly looking up whether a given Argument is in this ArgumentSCC.
655     for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end(); I != E; ++I) {
656       ArgumentSCCNodes.insert((*I)->Definition);
657     }
658 
659     for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
660          I != E && !SCCCaptured; ++I) {
661       ArgumentGraphNode *N = *I;
662       for (SmallVectorImpl<ArgumentGraphNode*>::iterator UI = N->Uses.begin(),
663              UE = N->Uses.end(); UI != UE; ++UI) {
664         Argument *A = (*UI)->Definition;
665         if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
666           continue;
667         SCCCaptured = true;
668         break;
669       }
670     }
671     if (SCCCaptured) continue;
672 
673     for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
674       Argument *A = ArgumentSCC[i]->Definition;
675       A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
676       ++NumNoCapture;
677       Changed = true;
678     }
679 
680     // We also want to compute readonly/readnone. With a small number of false
681     // negatives, we can assume that any pointer which is captured isn't going
682     // to be provably readonly or readnone, since by definition we can't
683     // analyze all uses of a captured pointer.
684     //
685     // The false negatives happen when the pointer is captured by a function
686     // that promises readonly/readnone behaviour on the pointer, then the
687     // pointer's lifetime ends before anything that writes to arbitrary memory.
688     // Also, a readonly/readnone pointer may be returned, but returning a
689     // pointer is capturing it.
690 
691     Attribute::AttrKind ReadAttr = Attribute::ReadNone;
692     for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
693       Argument *A = ArgumentSCC[i]->Definition;
694       Attribute::AttrKind K = determinePointerReadAttrs(A, ArgumentSCCNodes);
695       if (K == Attribute::ReadNone)
696         continue;
697       if (K == Attribute::ReadOnly) {
698         ReadAttr = Attribute::ReadOnly;
699         continue;
700       }
701       ReadAttr = K;
702       break;
703     }
704 
705     if (ReadAttr != Attribute::None) {
706       AttrBuilder B;
707       B.addAttribute(ReadAttr);
708       for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
709         Argument *A = ArgumentSCC[i]->Definition;
710         A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
711         ReadAttr == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
712         Changed = true;
713       }
714     }
715   }
716 
717   return Changed;
718 }
719 
720 /// IsFunctionMallocLike - A function is malloc-like if it returns either null
721 /// or a pointer that doesn't alias any other pointer visible to the caller.
722 bool FunctionAttrs::IsFunctionMallocLike(Function *F,
723                               SmallPtrSet<Function*, 8> &SCCNodes) const {
724   SmallSetVector<Value *, 8> FlowsToReturn;
725   for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
726     if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
727       FlowsToReturn.insert(Ret->getReturnValue());
728 
729   for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
730     Value *RetVal = FlowsToReturn[i];
731 
732     if (Constant *C = dyn_cast<Constant>(RetVal)) {
733       if (!C->isNullValue() && !isa<UndefValue>(C))
734         return false;
735 
736       continue;
737     }
738 
739     if (isa<Argument>(RetVal))
740       return false;
741 
742     if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
743       switch (RVI->getOpcode()) {
744         // Extend the analysis by looking upwards.
745         case Instruction::BitCast:
746         case Instruction::GetElementPtr:
747         case Instruction::AddrSpaceCast:
748           FlowsToReturn.insert(RVI->getOperand(0));
749           continue;
750         case Instruction::Select: {
751           SelectInst *SI = cast<SelectInst>(RVI);
752           FlowsToReturn.insert(SI->getTrueValue());
753           FlowsToReturn.insert(SI->getFalseValue());
754           continue;
755         }
756         case Instruction::PHI: {
757           PHINode *PN = cast<PHINode>(RVI);
758           for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
759             FlowsToReturn.insert(PN->getIncomingValue(i));
760           continue;
761         }
762 
763         // Check whether the pointer came from an allocation.
764         case Instruction::Alloca:
765           break;
766         case Instruction::Call:
767         case Instruction::Invoke: {
768           CallSite CS(RVI);
769           if (CS.paramHasAttr(0, Attribute::NoAlias))
770             break;
771           if (CS.getCalledFunction() &&
772               SCCNodes.count(CS.getCalledFunction()))
773             break;
774         } // fall-through
775         default:
776           return false;  // Did not come from an allocation.
777       }
778 
779     if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
780       return false;
781   }
782 
783   return true;
784 }
785 
786 /// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
787 bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
788   SmallPtrSet<Function*, 8> SCCNodes;
789 
790   // Fill SCCNodes with the elements of the SCC.  Used for quickly
791   // looking up whether a given CallGraphNode is in this SCC.
792   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
793     SCCNodes.insert((*I)->getFunction());
794 
795   // Check each function in turn, determining which functions return noalias
796   // pointers.
797   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
798     Function *F = (*I)->getFunction();
799 
800     if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
801       // External node or node we don't want to optimize - skip it;
802       return false;
803 
804     // Already noalias.
805     if (F->doesNotAlias(0))
806       continue;
807 
808     // Definitions with weak linkage may be overridden at linktime, so
809     // treat them like declarations.
810     if (F->isDeclaration() || F->mayBeOverridden())
811       return false;
812 
813     // We annotate noalias return values, which are only applicable to
814     // pointer types.
815     if (!F->getReturnType()->isPointerTy())
816       continue;
817 
818     if (!IsFunctionMallocLike(F, SCCNodes))
819       return false;
820   }
821 
822   bool MadeChange = false;
823   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
824     Function *F = (*I)->getFunction();
825     if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
826       continue;
827 
828     F->setDoesNotAlias(0);
829     ++NumNoAlias;
830     MadeChange = true;
831   }
832 
833   return MadeChange;
834 }
835 
836 /// inferPrototypeAttributes - Analyze the name and prototype of the
837 /// given function and set any applicable attributes.  Returns true
838 /// if any attributes were set and false otherwise.
839 bool FunctionAttrs::inferPrototypeAttributes(Function &F) {
840   if (F.hasFnAttribute(Attribute::OptimizeNone))
841     return false;
842 
843   FunctionType *FTy = F.getFunctionType();
844   LibFunc::Func TheLibFunc;
845   if (!(TLI->getLibFunc(F.getName(), TheLibFunc) && TLI->has(TheLibFunc)))
846     return false;
847 
848   switch (TheLibFunc) {
849   case LibFunc::strlen:
850     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
851       return false;
852     setOnlyReadsMemory(F);
853     setDoesNotThrow(F);
854     setDoesNotCapture(F, 1);
855     break;
856   case LibFunc::strchr:
857   case LibFunc::strrchr:
858     if (FTy->getNumParams() != 2 ||
859         !FTy->getParamType(0)->isPointerTy() ||
860         !FTy->getParamType(1)->isIntegerTy())
861       return false;
862     setOnlyReadsMemory(F);
863     setDoesNotThrow(F);
864     break;
865   case LibFunc::strtol:
866   case LibFunc::strtod:
867   case LibFunc::strtof:
868   case LibFunc::strtoul:
869   case LibFunc::strtoll:
870   case LibFunc::strtold:
871   case LibFunc::strtoull:
872     if (FTy->getNumParams() < 2 ||
873         !FTy->getParamType(1)->isPointerTy())
874       return false;
875     setDoesNotThrow(F);
876     setDoesNotCapture(F, 2);
877     setOnlyReadsMemory(F, 1);
878     break;
879   case LibFunc::strcpy:
880   case LibFunc::stpcpy:
881   case LibFunc::strcat:
882   case LibFunc::strncat:
883   case LibFunc::strncpy:
884   case LibFunc::stpncpy:
885     if (FTy->getNumParams() < 2 ||
886         !FTy->getParamType(1)->isPointerTy())
887       return false;
888     setDoesNotThrow(F);
889     setDoesNotCapture(F, 2);
890     setOnlyReadsMemory(F, 2);
891     break;
892   case LibFunc::strxfrm:
893     if (FTy->getNumParams() != 3 ||
894         !FTy->getParamType(0)->isPointerTy() ||
895         !FTy->getParamType(1)->isPointerTy())
896       return false;
897     setDoesNotThrow(F);
898     setDoesNotCapture(F, 1);
899     setDoesNotCapture(F, 2);
900     setOnlyReadsMemory(F, 2);
901     break;
902   case LibFunc::strcmp: //0,1
903     case LibFunc::strspn: // 0,1
904     case LibFunc::strncmp: // 0,1
905     case LibFunc::strcspn: //0,1
906     case LibFunc::strcoll: //0,1
907     case LibFunc::strcasecmp:  // 0,1
908     case LibFunc::strncasecmp: //
909     if (FTy->getNumParams() < 2 ||
910         !FTy->getParamType(0)->isPointerTy() ||
911         !FTy->getParamType(1)->isPointerTy())
912       return false;
913     setOnlyReadsMemory(F);
914     setDoesNotThrow(F);
915     setDoesNotCapture(F, 1);
916     setDoesNotCapture(F, 2);
917     break;
918   case LibFunc::strstr:
919   case LibFunc::strpbrk:
920     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
921       return false;
922     setOnlyReadsMemory(F);
923     setDoesNotThrow(F);
924     setDoesNotCapture(F, 2);
925     break;
926   case LibFunc::strtok:
927   case LibFunc::strtok_r:
928     if (FTy->getNumParams() < 2 || !FTy->getParamType(1)->isPointerTy())
929       return false;
930     setDoesNotThrow(F);
931     setDoesNotCapture(F, 2);
932     setOnlyReadsMemory(F, 2);
933     break;
934   case LibFunc::scanf:
935     if (FTy->getNumParams() < 1 || !FTy->getParamType(0)->isPointerTy())
936       return false;
937     setDoesNotThrow(F);
938     setDoesNotCapture(F, 1);
939     setOnlyReadsMemory(F, 1);
940     break;
941   case LibFunc::setbuf:
942   case LibFunc::setvbuf:
943     if (FTy->getNumParams() < 1 || !FTy->getParamType(0)->isPointerTy())
944       return false;
945     setDoesNotThrow(F);
946     setDoesNotCapture(F, 1);
947     break;
948   case LibFunc::strdup:
949   case LibFunc::strndup:
950     if (FTy->getNumParams() < 1 || !FTy->getReturnType()->isPointerTy() ||
951         !FTy->getParamType(0)->isPointerTy())
952       return false;
953     setDoesNotThrow(F);
954     setDoesNotAlias(F, 0);
955     setDoesNotCapture(F, 1);
956     setOnlyReadsMemory(F, 1);
957     break;
958   case LibFunc::stat:
959   case LibFunc::statvfs:
960     if (FTy->getNumParams() < 2 ||
961         !FTy->getParamType(0)->isPointerTy() ||
962         !FTy->getParamType(1)->isPointerTy())
963       return false;
964     setDoesNotThrow(F);
965     setDoesNotCapture(F, 1);
966     setDoesNotCapture(F, 2);
967     setOnlyReadsMemory(F, 1);
968     break;
969   case LibFunc::sscanf:
970     if (FTy->getNumParams() < 2 ||
971         !FTy->getParamType(0)->isPointerTy() ||
972         !FTy->getParamType(1)->isPointerTy())
973       return false;
974     setDoesNotThrow(F);
975     setDoesNotCapture(F, 1);
976     setDoesNotCapture(F, 2);
977     setOnlyReadsMemory(F, 1);
978     setOnlyReadsMemory(F, 2);
979     break;
980   case LibFunc::sprintf:
981     if (FTy->getNumParams() < 2 ||
982         !FTy->getParamType(0)->isPointerTy() ||
983         !FTy->getParamType(1)->isPointerTy())
984       return false;
985     setDoesNotThrow(F);
986     setDoesNotCapture(F, 1);
987     setDoesNotCapture(F, 2);
988     setOnlyReadsMemory(F, 2);
989     break;
990   case LibFunc::snprintf:
991     if (FTy->getNumParams() != 3 ||
992         !FTy->getParamType(0)->isPointerTy() ||
993         !FTy->getParamType(2)->isPointerTy())
994       return false;
995     setDoesNotThrow(F);
996     setDoesNotCapture(F, 1);
997     setDoesNotCapture(F, 3);
998     setOnlyReadsMemory(F, 3);
999     break;
1000   case LibFunc::setitimer:
1001     if (FTy->getNumParams() != 3 ||
1002         !FTy->getParamType(1)->isPointerTy() ||
1003         !FTy->getParamType(2)->isPointerTy())
1004       return false;
1005     setDoesNotThrow(F);
1006     setDoesNotCapture(F, 2);
1007     setDoesNotCapture(F, 3);
1008     setOnlyReadsMemory(F, 2);
1009     break;
1010   case LibFunc::system:
1011     if (FTy->getNumParams() != 1 ||
1012         !FTy->getParamType(0)->isPointerTy())
1013       return false;
1014     // May throw; "system" is a valid pthread cancellation point.
1015     setDoesNotCapture(F, 1);
1016     setOnlyReadsMemory(F, 1);
1017     break;
1018   case LibFunc::malloc:
1019     if (FTy->getNumParams() != 1 ||
1020         !FTy->getReturnType()->isPointerTy())
1021       return false;
1022     setDoesNotThrow(F);
1023     setDoesNotAlias(F, 0);
1024     break;
1025   case LibFunc::memcmp:
1026     if (FTy->getNumParams() != 3 ||
1027         !FTy->getParamType(0)->isPointerTy() ||
1028         !FTy->getParamType(1)->isPointerTy())
1029       return false;
1030     setOnlyReadsMemory(F);
1031     setDoesNotThrow(F);
1032     setDoesNotCapture(F, 1);
1033     setDoesNotCapture(F, 2);
1034     break;
1035   case LibFunc::memchr:
1036   case LibFunc::memrchr:
1037     if (FTy->getNumParams() != 3)
1038       return false;
1039     setOnlyReadsMemory(F);
1040     setDoesNotThrow(F);
1041     break;
1042   case LibFunc::modf:
1043   case LibFunc::modff:
1044   case LibFunc::modfl:
1045     if (FTy->getNumParams() < 2 ||
1046         !FTy->getParamType(1)->isPointerTy())
1047       return false;
1048     setDoesNotThrow(F);
1049     setDoesNotCapture(F, 2);
1050     break;
1051   case LibFunc::memcpy:
1052   case LibFunc::memccpy:
1053   case LibFunc::memmove:
1054     if (FTy->getNumParams() < 2 ||
1055         !FTy->getParamType(1)->isPointerTy())
1056       return false;
1057     setDoesNotThrow(F);
1058     setDoesNotCapture(F, 2);
1059     setOnlyReadsMemory(F, 2);
1060     break;
1061   case LibFunc::memalign:
1062     if (!FTy->getReturnType()->isPointerTy())
1063       return false;
1064     setDoesNotAlias(F, 0);
1065     break;
1066   case LibFunc::mkdir:
1067     if (FTy->getNumParams() == 0 ||
1068         !FTy->getParamType(0)->isPointerTy())
1069       return false;
1070     setDoesNotThrow(F);
1071     setDoesNotCapture(F, 1);
1072     setOnlyReadsMemory(F, 1);
1073     break;
1074   case LibFunc::mktime:
1075     if (FTy->getNumParams() == 0 ||
1076         !FTy->getParamType(0)->isPointerTy())
1077       return false;
1078     setDoesNotThrow(F);
1079     setDoesNotCapture(F, 1);
1080     break;
1081   case LibFunc::realloc:
1082     if (FTy->getNumParams() != 2 ||
1083         !FTy->getParamType(0)->isPointerTy() ||
1084         !FTy->getReturnType()->isPointerTy())
1085       return false;
1086     setDoesNotThrow(F);
1087     setDoesNotAlias(F, 0);
1088     setDoesNotCapture(F, 1);
1089     break;
1090   case LibFunc::read:
1091     if (FTy->getNumParams() != 3 ||
1092         !FTy->getParamType(1)->isPointerTy())
1093       return false;
1094     // May throw; "read" is a valid pthread cancellation point.
1095     setDoesNotCapture(F, 2);
1096     break;
1097   case LibFunc::rewind:
1098     if (FTy->getNumParams() < 1 ||
1099         !FTy->getParamType(0)->isPointerTy())
1100       return false;
1101     setDoesNotThrow(F);
1102     setDoesNotCapture(F, 1);
1103     break;
1104   case LibFunc::rmdir:
1105   case LibFunc::remove:
1106   case LibFunc::realpath:
1107     if (FTy->getNumParams() < 1 ||
1108         !FTy->getParamType(0)->isPointerTy())
1109       return false;
1110     setDoesNotThrow(F);
1111     setDoesNotCapture(F, 1);
1112     setOnlyReadsMemory(F, 1);
1113     break;
1114   case LibFunc::rename:
1115     if (FTy->getNumParams() < 2 ||
1116         !FTy->getParamType(0)->isPointerTy() ||
1117         !FTy->getParamType(1)->isPointerTy())
1118       return false;
1119     setDoesNotThrow(F);
1120     setDoesNotCapture(F, 1);
1121     setDoesNotCapture(F, 2);
1122     setOnlyReadsMemory(F, 1);
1123     setOnlyReadsMemory(F, 2);
1124     break;
1125   case LibFunc::readlink:
1126     if (FTy->getNumParams() < 2 ||
1127         !FTy->getParamType(0)->isPointerTy() ||
1128         !FTy->getParamType(1)->isPointerTy())
1129       return false;
1130     setDoesNotThrow(F);
1131     setDoesNotCapture(F, 1);
1132     setDoesNotCapture(F, 2);
1133     setOnlyReadsMemory(F, 1);
1134     break;
1135   case LibFunc::write:
1136     if (FTy->getNumParams() != 3 || !FTy->getParamType(1)->isPointerTy())
1137       return false;
1138     // May throw; "write" is a valid pthread cancellation point.
1139     setDoesNotCapture(F, 2);
1140     setOnlyReadsMemory(F, 2);
1141     break;
1142   case LibFunc::bcopy:
1143     if (FTy->getNumParams() != 3 ||
1144         !FTy->getParamType(0)->isPointerTy() ||
1145         !FTy->getParamType(1)->isPointerTy())
1146       return false;
1147     setDoesNotThrow(F);
1148     setDoesNotCapture(F, 1);
1149     setDoesNotCapture(F, 2);
1150     setOnlyReadsMemory(F, 1);
1151     break;
1152   case LibFunc::bcmp:
1153     if (FTy->getNumParams() != 3 ||
1154         !FTy->getParamType(0)->isPointerTy() ||
1155         !FTy->getParamType(1)->isPointerTy())
1156       return false;
1157     setDoesNotThrow(F);
1158     setOnlyReadsMemory(F);
1159     setDoesNotCapture(F, 1);
1160     setDoesNotCapture(F, 2);
1161     break;
1162   case LibFunc::bzero:
1163     if (FTy->getNumParams() != 2 || !FTy->getParamType(0)->isPointerTy())
1164       return false;
1165     setDoesNotThrow(F);
1166     setDoesNotCapture(F, 1);
1167     break;
1168   case LibFunc::calloc:
1169     if (FTy->getNumParams() != 2 ||
1170         !FTy->getReturnType()->isPointerTy())
1171       return false;
1172     setDoesNotThrow(F);
1173     setDoesNotAlias(F, 0);
1174     break;
1175   case LibFunc::chmod:
1176   case LibFunc::chown:
1177     if (FTy->getNumParams() == 0 || !FTy->getParamType(0)->isPointerTy())
1178       return false;
1179     setDoesNotThrow(F);
1180     setDoesNotCapture(F, 1);
1181     setOnlyReadsMemory(F, 1);
1182     break;
1183   case LibFunc::ctermid:
1184   case LibFunc::clearerr:
1185   case LibFunc::closedir:
1186     if (FTy->getNumParams() == 0 || !FTy->getParamType(0)->isPointerTy())
1187       return false;
1188     setDoesNotThrow(F);
1189     setDoesNotCapture(F, 1);
1190     break;
1191   case LibFunc::atoi:
1192   case LibFunc::atol:
1193   case LibFunc::atof:
1194   case LibFunc::atoll:
1195     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1196       return false;
1197     setDoesNotThrow(F);
1198     setOnlyReadsMemory(F);
1199     setDoesNotCapture(F, 1);
1200     break;
1201   case LibFunc::access:
1202     if (FTy->getNumParams() != 2 || !FTy->getParamType(0)->isPointerTy())
1203       return false;
1204     setDoesNotThrow(F);
1205     setDoesNotCapture(F, 1);
1206     setOnlyReadsMemory(F, 1);
1207     break;
1208   case LibFunc::fopen:
1209     if (FTy->getNumParams() != 2 ||
1210         !FTy->getReturnType()->isPointerTy() ||
1211         !FTy->getParamType(0)->isPointerTy() ||
1212         !FTy->getParamType(1)->isPointerTy())
1213       return false;
1214     setDoesNotThrow(F);
1215     setDoesNotAlias(F, 0);
1216     setDoesNotCapture(F, 1);
1217     setDoesNotCapture(F, 2);
1218     setOnlyReadsMemory(F, 1);
1219     setOnlyReadsMemory(F, 2);
1220     break;
1221   case LibFunc::fdopen:
1222     if (FTy->getNumParams() != 2 ||
1223         !FTy->getReturnType()->isPointerTy() ||
1224         !FTy->getParamType(1)->isPointerTy())
1225       return false;
1226     setDoesNotThrow(F);
1227     setDoesNotAlias(F, 0);
1228     setDoesNotCapture(F, 2);
1229     setOnlyReadsMemory(F, 2);
1230     break;
1231   case LibFunc::feof:
1232   case LibFunc::free:
1233   case LibFunc::fseek:
1234   case LibFunc::ftell:
1235   case LibFunc::fgetc:
1236   case LibFunc::fseeko:
1237   case LibFunc::ftello:
1238   case LibFunc::fileno:
1239   case LibFunc::fflush:
1240   case LibFunc::fclose:
1241   case LibFunc::fsetpos:
1242   case LibFunc::flockfile:
1243   case LibFunc::funlockfile:
1244   case LibFunc::ftrylockfile:
1245     if (FTy->getNumParams() == 0 || !FTy->getParamType(0)->isPointerTy())
1246       return false;
1247     setDoesNotThrow(F);
1248     setDoesNotCapture(F, 1);
1249     break;
1250   case LibFunc::ferror:
1251     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1252       return false;
1253     setDoesNotThrow(F);
1254     setDoesNotCapture(F, 1);
1255     setOnlyReadsMemory(F);
1256     break;
1257   case LibFunc::fputc:
1258   case LibFunc::fstat:
1259   case LibFunc::frexp:
1260   case LibFunc::frexpf:
1261   case LibFunc::frexpl:
1262   case LibFunc::fstatvfs:
1263     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1264       return false;
1265     setDoesNotThrow(F);
1266     setDoesNotCapture(F, 2);
1267     break;
1268   case LibFunc::fgets:
1269     if (FTy->getNumParams() != 3 ||
1270         !FTy->getParamType(0)->isPointerTy() ||
1271         !FTy->getParamType(2)->isPointerTy())
1272       return false;
1273     setDoesNotThrow(F);
1274     setDoesNotCapture(F, 3);
1275     break;
1276   case LibFunc::fread:
1277     if (FTy->getNumParams() != 4 ||
1278         !FTy->getParamType(0)->isPointerTy() ||
1279         !FTy->getParamType(3)->isPointerTy())
1280       return false;
1281     setDoesNotThrow(F);
1282     setDoesNotCapture(F, 1);
1283     setDoesNotCapture(F, 4);
1284     break;
1285   case LibFunc::fwrite:
1286     if (FTy->getNumParams() != 4 ||
1287         !FTy->getParamType(0)->isPointerTy() ||
1288         !FTy->getParamType(3)->isPointerTy())
1289       return false;
1290     setDoesNotThrow(F);
1291     setDoesNotCapture(F, 1);
1292     setDoesNotCapture(F, 4);
1293     break;
1294   case LibFunc::fputs:
1295     if (FTy->getNumParams() < 2 ||
1296         !FTy->getParamType(0)->isPointerTy() ||
1297         !FTy->getParamType(1)->isPointerTy())
1298       return false;
1299     setDoesNotThrow(F);
1300     setDoesNotCapture(F, 1);
1301     setDoesNotCapture(F, 2);
1302     setOnlyReadsMemory(F, 1);
1303     break;
1304   case LibFunc::fscanf:
1305   case LibFunc::fprintf:
1306     if (FTy->getNumParams() < 2 ||
1307         !FTy->getParamType(0)->isPointerTy() ||
1308         !FTy->getParamType(1)->isPointerTy())
1309       return false;
1310     setDoesNotThrow(F);
1311     setDoesNotCapture(F, 1);
1312     setDoesNotCapture(F, 2);
1313     setOnlyReadsMemory(F, 2);
1314     break;
1315   case LibFunc::fgetpos:
1316     if (FTy->getNumParams() < 2 ||
1317         !FTy->getParamType(0)->isPointerTy() ||
1318         !FTy->getParamType(1)->isPointerTy())
1319       return false;
1320     setDoesNotThrow(F);
1321     setDoesNotCapture(F, 1);
1322     setDoesNotCapture(F, 2);
1323     break;
1324   case LibFunc::getc:
1325   case LibFunc::getlogin_r:
1326   case LibFunc::getc_unlocked:
1327     if (FTy->getNumParams() == 0 || !FTy->getParamType(0)->isPointerTy())
1328       return false;
1329     setDoesNotThrow(F);
1330     setDoesNotCapture(F, 1);
1331     break;
1332   case LibFunc::getenv:
1333     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1334       return false;
1335     setDoesNotThrow(F);
1336     setOnlyReadsMemory(F);
1337     setDoesNotCapture(F, 1);
1338     break;
1339   case LibFunc::gets:
1340   case LibFunc::getchar:
1341     setDoesNotThrow(F);
1342     break;
1343   case LibFunc::getitimer:
1344     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1345       return false;
1346     setDoesNotThrow(F);
1347     setDoesNotCapture(F, 2);
1348     break;
1349   case LibFunc::getpwnam:
1350     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1351       return false;
1352     setDoesNotThrow(F);
1353     setDoesNotCapture(F, 1);
1354     setOnlyReadsMemory(F, 1);
1355     break;
1356   case LibFunc::ungetc:
1357     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1358       return false;
1359     setDoesNotThrow(F);
1360     setDoesNotCapture(F, 2);
1361     break;
1362   case LibFunc::uname:
1363     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1364       return false;
1365     setDoesNotThrow(F);
1366     setDoesNotCapture(F, 1);
1367     break;
1368   case LibFunc::unlink:
1369     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1370       return false;
1371     setDoesNotThrow(F);
1372     setDoesNotCapture(F, 1);
1373     setOnlyReadsMemory(F, 1);
1374     break;
1375   case LibFunc::unsetenv:
1376     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1377       return false;
1378     setDoesNotThrow(F);
1379     setDoesNotCapture(F, 1);
1380     setOnlyReadsMemory(F, 1);
1381     break;
1382   case LibFunc::utime:
1383   case LibFunc::utimes:
1384     if (FTy->getNumParams() != 2 ||
1385         !FTy->getParamType(0)->isPointerTy() ||
1386         !FTy->getParamType(1)->isPointerTy())
1387       return false;
1388     setDoesNotThrow(F);
1389     setDoesNotCapture(F, 1);
1390     setDoesNotCapture(F, 2);
1391     setOnlyReadsMemory(F, 1);
1392     setOnlyReadsMemory(F, 2);
1393     break;
1394   case LibFunc::putc:
1395     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1396       return false;
1397     setDoesNotThrow(F);
1398     setDoesNotCapture(F, 2);
1399     break;
1400   case LibFunc::puts:
1401   case LibFunc::printf:
1402   case LibFunc::perror:
1403     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1404       return false;
1405     setDoesNotThrow(F);
1406     setDoesNotCapture(F, 1);
1407     setOnlyReadsMemory(F, 1);
1408     break;
1409   case LibFunc::pread:
1410     if (FTy->getNumParams() != 4 || !FTy->getParamType(1)->isPointerTy())
1411       return false;
1412     // May throw; "pread" is a valid pthread cancellation point.
1413     setDoesNotCapture(F, 2);
1414     break;
1415   case LibFunc::pwrite:
1416     if (FTy->getNumParams() != 4 || !FTy->getParamType(1)->isPointerTy())
1417       return false;
1418     // May throw; "pwrite" is a valid pthread cancellation point.
1419     setDoesNotCapture(F, 2);
1420     setOnlyReadsMemory(F, 2);
1421     break;
1422   case LibFunc::putchar:
1423     setDoesNotThrow(F);
1424     break;
1425   case LibFunc::popen:
1426     if (FTy->getNumParams() != 2 ||
1427         !FTy->getReturnType()->isPointerTy() ||
1428         !FTy->getParamType(0)->isPointerTy() ||
1429         !FTy->getParamType(1)->isPointerTy())
1430       return false;
1431     setDoesNotThrow(F);
1432     setDoesNotAlias(F, 0);
1433     setDoesNotCapture(F, 1);
1434     setDoesNotCapture(F, 2);
1435     setOnlyReadsMemory(F, 1);
1436     setOnlyReadsMemory(F, 2);
1437     break;
1438   case LibFunc::pclose:
1439     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1440       return false;
1441     setDoesNotThrow(F);
1442     setDoesNotCapture(F, 1);
1443     break;
1444   case LibFunc::vscanf:
1445     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1446       return false;
1447     setDoesNotThrow(F);
1448     setDoesNotCapture(F, 1);
1449     setOnlyReadsMemory(F, 1);
1450     break;
1451   case LibFunc::vsscanf:
1452     if (FTy->getNumParams() != 3 ||
1453         !FTy->getParamType(1)->isPointerTy() ||
1454         !FTy->getParamType(2)->isPointerTy())
1455       return false;
1456     setDoesNotThrow(F);
1457     setDoesNotCapture(F, 1);
1458     setDoesNotCapture(F, 2);
1459     setOnlyReadsMemory(F, 1);
1460     setOnlyReadsMemory(F, 2);
1461     break;
1462   case LibFunc::vfscanf:
1463     if (FTy->getNumParams() != 3 ||
1464         !FTy->getParamType(1)->isPointerTy() ||
1465         !FTy->getParamType(2)->isPointerTy())
1466       return false;
1467     setDoesNotThrow(F);
1468     setDoesNotCapture(F, 1);
1469     setDoesNotCapture(F, 2);
1470     setOnlyReadsMemory(F, 2);
1471     break;
1472   case LibFunc::valloc:
1473     if (!FTy->getReturnType()->isPointerTy())
1474       return false;
1475     setDoesNotThrow(F);
1476     setDoesNotAlias(F, 0);
1477     break;
1478   case LibFunc::vprintf:
1479     if (FTy->getNumParams() != 2 || !FTy->getParamType(0)->isPointerTy())
1480       return false;
1481     setDoesNotThrow(F);
1482     setDoesNotCapture(F, 1);
1483     setOnlyReadsMemory(F, 1);
1484     break;
1485   case LibFunc::vfprintf:
1486   case LibFunc::vsprintf:
1487     if (FTy->getNumParams() != 3 ||
1488         !FTy->getParamType(0)->isPointerTy() ||
1489         !FTy->getParamType(1)->isPointerTy())
1490       return false;
1491     setDoesNotThrow(F);
1492     setDoesNotCapture(F, 1);
1493     setDoesNotCapture(F, 2);
1494     setOnlyReadsMemory(F, 2);
1495     break;
1496   case LibFunc::vsnprintf:
1497     if (FTy->getNumParams() != 4 ||
1498         !FTy->getParamType(0)->isPointerTy() ||
1499         !FTy->getParamType(2)->isPointerTy())
1500       return false;
1501     setDoesNotThrow(F);
1502     setDoesNotCapture(F, 1);
1503     setDoesNotCapture(F, 3);
1504     setOnlyReadsMemory(F, 3);
1505     break;
1506   case LibFunc::open:
1507     if (FTy->getNumParams() < 2 || !FTy->getParamType(0)->isPointerTy())
1508       return false;
1509     // May throw; "open" is a valid pthread cancellation point.
1510     setDoesNotCapture(F, 1);
1511     setOnlyReadsMemory(F, 1);
1512     break;
1513   case LibFunc::opendir:
1514     if (FTy->getNumParams() != 1 ||
1515         !FTy->getReturnType()->isPointerTy() ||
1516         !FTy->getParamType(0)->isPointerTy())
1517       return false;
1518     setDoesNotThrow(F);
1519     setDoesNotAlias(F, 0);
1520     setDoesNotCapture(F, 1);
1521     setOnlyReadsMemory(F, 1);
1522     break;
1523   case LibFunc::tmpfile:
1524     if (!FTy->getReturnType()->isPointerTy())
1525       return false;
1526     setDoesNotThrow(F);
1527     setDoesNotAlias(F, 0);
1528     break;
1529   case LibFunc::times:
1530     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1531       return false;
1532     setDoesNotThrow(F);
1533     setDoesNotCapture(F, 1);
1534     break;
1535   case LibFunc::htonl:
1536   case LibFunc::htons:
1537   case LibFunc::ntohl:
1538   case LibFunc::ntohs:
1539     setDoesNotThrow(F);
1540     setDoesNotAccessMemory(F);
1541     break;
1542   case LibFunc::lstat:
1543     if (FTy->getNumParams() != 2 ||
1544         !FTy->getParamType(0)->isPointerTy() ||
1545         !FTy->getParamType(1)->isPointerTy())
1546       return false;
1547     setDoesNotThrow(F);
1548     setDoesNotCapture(F, 1);
1549     setDoesNotCapture(F, 2);
1550     setOnlyReadsMemory(F, 1);
1551     break;
1552   case LibFunc::lchown:
1553     if (FTy->getNumParams() != 3 || !FTy->getParamType(0)->isPointerTy())
1554       return false;
1555     setDoesNotThrow(F);
1556     setDoesNotCapture(F, 1);
1557     setOnlyReadsMemory(F, 1);
1558     break;
1559   case LibFunc::qsort:
1560     if (FTy->getNumParams() != 4 || !FTy->getParamType(3)->isPointerTy())
1561       return false;
1562     // May throw; places call through function pointer.
1563     setDoesNotCapture(F, 4);
1564     break;
1565   case LibFunc::dunder_strdup:
1566   case LibFunc::dunder_strndup:
1567     if (FTy->getNumParams() < 1 ||
1568         !FTy->getReturnType()->isPointerTy() ||
1569         !FTy->getParamType(0)->isPointerTy())
1570       return false;
1571     setDoesNotThrow(F);
1572     setDoesNotAlias(F, 0);
1573     setDoesNotCapture(F, 1);
1574     setOnlyReadsMemory(F, 1);
1575     break;
1576   case LibFunc::dunder_strtok_r:
1577     if (FTy->getNumParams() != 3 ||
1578         !FTy->getParamType(1)->isPointerTy())
1579       return false;
1580     setDoesNotThrow(F);
1581     setDoesNotCapture(F, 2);
1582     setOnlyReadsMemory(F, 2);
1583     break;
1584   case LibFunc::under_IO_getc:
1585     if (FTy->getNumParams() != 1 || !FTy->getParamType(0)->isPointerTy())
1586       return false;
1587     setDoesNotThrow(F);
1588     setDoesNotCapture(F, 1);
1589     break;
1590   case LibFunc::under_IO_putc:
1591     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1592       return false;
1593     setDoesNotThrow(F);
1594     setDoesNotCapture(F, 2);
1595     break;
1596   case LibFunc::dunder_isoc99_scanf:
1597     if (FTy->getNumParams() < 1 ||
1598         !FTy->getParamType(0)->isPointerTy())
1599       return false;
1600     setDoesNotThrow(F);
1601     setDoesNotCapture(F, 1);
1602     setOnlyReadsMemory(F, 1);
1603     break;
1604   case LibFunc::stat64:
1605   case LibFunc::lstat64:
1606   case LibFunc::statvfs64:
1607     if (FTy->getNumParams() < 1 ||
1608         !FTy->getParamType(0)->isPointerTy() ||
1609         !FTy->getParamType(1)->isPointerTy())
1610       return false;
1611     setDoesNotThrow(F);
1612     setDoesNotCapture(F, 1);
1613     setDoesNotCapture(F, 2);
1614     setOnlyReadsMemory(F, 1);
1615     break;
1616   case LibFunc::dunder_isoc99_sscanf:
1617     if (FTy->getNumParams() < 1 ||
1618         !FTy->getParamType(0)->isPointerTy() ||
1619         !FTy->getParamType(1)->isPointerTy())
1620       return false;
1621     setDoesNotThrow(F);
1622     setDoesNotCapture(F, 1);
1623     setDoesNotCapture(F, 2);
1624     setOnlyReadsMemory(F, 1);
1625     setOnlyReadsMemory(F, 2);
1626     break;
1627   case LibFunc::fopen64:
1628     if (FTy->getNumParams() != 2 ||
1629         !FTy->getReturnType()->isPointerTy() ||
1630         !FTy->getParamType(0)->isPointerTy() ||
1631         !FTy->getParamType(1)->isPointerTy())
1632       return false;
1633     setDoesNotThrow(F);
1634     setDoesNotAlias(F, 0);
1635     setDoesNotCapture(F, 1);
1636     setDoesNotCapture(F, 2);
1637     setOnlyReadsMemory(F, 1);
1638     setOnlyReadsMemory(F, 2);
1639     break;
1640   case LibFunc::fseeko64:
1641   case LibFunc::ftello64:
1642     if (FTy->getNumParams() == 0 || !FTy->getParamType(0)->isPointerTy())
1643       return false;
1644     setDoesNotThrow(F);
1645     setDoesNotCapture(F, 1);
1646     break;
1647   case LibFunc::tmpfile64:
1648     if (!FTy->getReturnType()->isPointerTy())
1649       return false;
1650     setDoesNotThrow(F);
1651     setDoesNotAlias(F, 0);
1652     break;
1653   case LibFunc::fstat64:
1654   case LibFunc::fstatvfs64:
1655     if (FTy->getNumParams() != 2 || !FTy->getParamType(1)->isPointerTy())
1656       return false;
1657     setDoesNotThrow(F);
1658     setDoesNotCapture(F, 2);
1659     break;
1660   case LibFunc::open64:
1661     if (FTy->getNumParams() < 2 || !FTy->getParamType(0)->isPointerTy())
1662       return false;
1663     // May throw; "open" is a valid pthread cancellation point.
1664     setDoesNotCapture(F, 1);
1665     setOnlyReadsMemory(F, 1);
1666     break;
1667   case LibFunc::gettimeofday:
1668     if (FTy->getNumParams() != 2 || !FTy->getParamType(0)->isPointerTy() ||
1669         !FTy->getParamType(1)->isPointerTy())
1670       return false;
1671     // Currently some platforms have the restrict keyword on the arguments to
1672     // gettimeofday. To be conservative, do not add noalias to gettimeofday's
1673     // arguments.
1674     setDoesNotThrow(F);
1675     setDoesNotCapture(F, 1);
1676     setDoesNotCapture(F, 2);
1677     break;
1678   default:
1679     // Didn't mark any attributes.
1680     return false;
1681   }
1682 
1683   return true;
1684 }
1685 
1686 /// annotateLibraryCalls - Adds attributes to well-known standard library
1687 /// call declarations.
1688 bool FunctionAttrs::annotateLibraryCalls(const CallGraphSCC &SCC) {
1689   bool MadeChange = false;
1690 
1691   // Check each function in turn annotating well-known library function
1692   // declarations with attributes.
1693   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
1694     Function *F = (*I)->getFunction();
1695 
1696     if (F && F->isDeclaration())
1697       MadeChange |= inferPrototypeAttributes(*F);
1698   }
1699 
1700   return MadeChange;
1701 }
1702 
1703 bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
1704   AA = &getAnalysis<AliasAnalysis>();
1705   TLI = &getAnalysis<TargetLibraryInfo>();
1706 
1707   bool Changed = annotateLibraryCalls(SCC);
1708   Changed |= AddReadAttrs(SCC);
1709   Changed |= AddArgumentAttrs(SCC);
1710   Changed |= AddNoAliasAttrs(SCC);
1711   return Changed;
1712 }
1713