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