1 //===- AliasAnalysisEvaluator.cpp - Alias Analysis Accuracy Evaluator -----===//
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 N^2 alias analysis accuracy evaluator.
11 // Basically, for each function in the program, it simply queries to see how the
12 // alias analysis implementation answers alias queries between each pair of
13 // pointers in the function.
14 //
15 // This is inspired and adapted from code by: Naveen Neelakantam, Francesco
16 // Spadini, and Wojciech Stryjewski.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #include "llvm/Analysis/Passes.h"
21 #include "llvm/ADT/SetVector.h"
22 #include "llvm/Analysis/AliasAnalysis.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/IR/InstIterator.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/raw_ostream.h"
34 using namespace llvm;
35 
36 static cl::opt<bool> PrintAll("print-all-alias-modref-info", cl::ReallyHidden);
37 
38 static cl::opt<bool> PrintNoAlias("print-no-aliases", cl::ReallyHidden);
39 static cl::opt<bool> PrintMayAlias("print-may-aliases", cl::ReallyHidden);
40 static cl::opt<bool> PrintPartialAlias("print-partial-aliases", cl::ReallyHidden);
41 static cl::opt<bool> PrintMustAlias("print-must-aliases", cl::ReallyHidden);
42 
43 static cl::opt<bool> PrintNoModRef("print-no-modref", cl::ReallyHidden);
44 static cl::opt<bool> PrintMod("print-mod", cl::ReallyHidden);
45 static cl::opt<bool> PrintRef("print-ref", cl::ReallyHidden);
46 static cl::opt<bool> PrintModRef("print-modref", cl::ReallyHidden);
47 
48 static cl::opt<bool> EvalAAMD("evaluate-aa-metadata", cl::ReallyHidden);
49 
50 namespace {
51   class AAEval : public FunctionPass {
52     unsigned NoAliasCount, MayAliasCount, PartialAliasCount, MustAliasCount;
53     unsigned NoModRefCount, ModCount, RefCount, ModRefCount;
54 
55   public:
56     static char ID; // Pass identification, replacement for typeid
AAEval()57     AAEval() : FunctionPass(ID) {
58       initializeAAEvalPass(*PassRegistry::getPassRegistry());
59     }
60 
getAnalysisUsage(AnalysisUsage & AU) const61     void getAnalysisUsage(AnalysisUsage &AU) const override {
62       AU.addRequired<AAResultsWrapperPass>();
63       AU.setPreservesAll();
64     }
65 
doInitialization(Module & M)66     bool doInitialization(Module &M) override {
67       NoAliasCount = MayAliasCount = PartialAliasCount = MustAliasCount = 0;
68       NoModRefCount = ModCount = RefCount = ModRefCount = 0;
69 
70       if (PrintAll) {
71         PrintNoAlias = PrintMayAlias = true;
72         PrintPartialAlias = PrintMustAlias = true;
73         PrintNoModRef = PrintMod = PrintRef = PrintModRef = true;
74       }
75       return false;
76     }
77 
78     bool runOnFunction(Function &F) override;
79     bool doFinalization(Module &M) override;
80   };
81 }
82 
83 char AAEval::ID = 0;
84 INITIALIZE_PASS_BEGIN(AAEval, "aa-eval",
85                 "Exhaustive Alias Analysis Precision Evaluator", false, true)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)86 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
87 INITIALIZE_PASS_END(AAEval, "aa-eval",
88                 "Exhaustive Alias Analysis Precision Evaluator", false, true)
89 
90 FunctionPass *llvm::createAAEvalPass() { return new AAEval(); }
91 
PrintResults(const char * Msg,bool P,const Value * V1,const Value * V2,const Module * M)92 static void PrintResults(const char *Msg, bool P, const Value *V1,
93                          const Value *V2, const Module *M) {
94   if (P) {
95     std::string o1, o2;
96     {
97       raw_string_ostream os1(o1), os2(o2);
98       V1->printAsOperand(os1, true, M);
99       V2->printAsOperand(os2, true, M);
100     }
101 
102     if (o2 < o1)
103       std::swap(o1, o2);
104     errs() << "  " << Msg << ":\t"
105            << o1 << ", "
106            << o2 << "\n";
107   }
108 }
109 
110 static inline void
PrintModRefResults(const char * Msg,bool P,Instruction * I,Value * Ptr,Module * M)111 PrintModRefResults(const char *Msg, bool P, Instruction *I, Value *Ptr,
112                    Module *M) {
113   if (P) {
114     errs() << "  " << Msg << ":  Ptr: ";
115     Ptr->printAsOperand(errs(), true, M);
116     errs() << "\t<->" << *I << '\n';
117   }
118 }
119 
120 static inline void
PrintModRefResults(const char * Msg,bool P,CallSite CSA,CallSite CSB,Module * M)121 PrintModRefResults(const char *Msg, bool P, CallSite CSA, CallSite CSB,
122                    Module *M) {
123   if (P) {
124     errs() << "  " << Msg << ": " << *CSA.getInstruction()
125            << " <-> " << *CSB.getInstruction() << '\n';
126   }
127 }
128 
129 static inline void
PrintLoadStoreResults(const char * Msg,bool P,const Value * V1,const Value * V2,const Module * M)130 PrintLoadStoreResults(const char *Msg, bool P, const Value *V1,
131                       const Value *V2, const Module *M) {
132   if (P) {
133     errs() << "  " << Msg << ": " << *V1
134            << " <-> " << *V2 << '\n';
135   }
136 }
137 
isInterestingPointer(Value * V)138 static inline bool isInterestingPointer(Value *V) {
139   return V->getType()->isPointerTy()
140       && !isa<ConstantPointerNull>(V);
141 }
142 
runOnFunction(Function & F)143 bool AAEval::runOnFunction(Function &F) {
144   const DataLayout &DL = F.getParent()->getDataLayout();
145   AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
146 
147   SetVector<Value *> Pointers;
148   SmallSetVector<CallSite, 16> CallSites;
149   SetVector<Value *> Loads;
150   SetVector<Value *> Stores;
151 
152   for (auto &I : F.args())
153     if (I.getType()->isPointerTy())    // Add all pointer arguments.
154       Pointers.insert(&I);
155 
156   for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
157     if (I->getType()->isPointerTy()) // Add all pointer instructions.
158       Pointers.insert(&*I);
159     if (EvalAAMD && isa<LoadInst>(&*I))
160       Loads.insert(&*I);
161     if (EvalAAMD && isa<StoreInst>(&*I))
162       Stores.insert(&*I);
163     Instruction &Inst = *I;
164     if (auto CS = CallSite(&Inst)) {
165       Value *Callee = CS.getCalledValue();
166       // Skip actual functions for direct function calls.
167       if (!isa<Function>(Callee) && isInterestingPointer(Callee))
168         Pointers.insert(Callee);
169       // Consider formals.
170       for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
171            AI != AE; ++AI)
172         if (isInterestingPointer(*AI))
173           Pointers.insert(*AI);
174       CallSites.insert(CS);
175     } else {
176       // Consider all operands.
177       for (Instruction::op_iterator OI = Inst.op_begin(), OE = Inst.op_end();
178            OI != OE; ++OI)
179         if (isInterestingPointer(*OI))
180           Pointers.insert(*OI);
181     }
182   }
183 
184   if (PrintNoAlias || PrintMayAlias || PrintPartialAlias || PrintMustAlias ||
185       PrintNoModRef || PrintMod || PrintRef || PrintModRef)
186     errs() << "Function: " << F.getName() << ": " << Pointers.size()
187            << " pointers, " << CallSites.size() << " call sites\n";
188 
189   // iterate over the worklist, and run the full (n^2)/2 disambiguations
190   for (SetVector<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
191        I1 != E; ++I1) {
192     uint64_t I1Size = MemoryLocation::UnknownSize;
193     Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
194     if (I1ElTy->isSized()) I1Size = DL.getTypeStoreSize(I1ElTy);
195 
196     for (SetVector<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
197       uint64_t I2Size = MemoryLocation::UnknownSize;
198       Type *I2ElTy =cast<PointerType>((*I2)->getType())->getElementType();
199       if (I2ElTy->isSized()) I2Size = DL.getTypeStoreSize(I2ElTy);
200 
201       switch (AA.alias(*I1, I1Size, *I2, I2Size)) {
202       case NoAlias:
203         PrintResults("NoAlias", PrintNoAlias, *I1, *I2, F.getParent());
204         ++NoAliasCount;
205         break;
206       case MayAlias:
207         PrintResults("MayAlias", PrintMayAlias, *I1, *I2, F.getParent());
208         ++MayAliasCount;
209         break;
210       case PartialAlias:
211         PrintResults("PartialAlias", PrintPartialAlias, *I1, *I2,
212                      F.getParent());
213         ++PartialAliasCount;
214         break;
215       case MustAlias:
216         PrintResults("MustAlias", PrintMustAlias, *I1, *I2, F.getParent());
217         ++MustAliasCount;
218         break;
219       }
220     }
221   }
222 
223   if (EvalAAMD) {
224     // iterate over all pairs of load, store
225     for (SetVector<Value *>::iterator I1 = Loads.begin(), E = Loads.end();
226          I1 != E; ++I1) {
227       for (SetVector<Value *>::iterator I2 = Stores.begin(), E2 = Stores.end();
228            I2 != E2; ++I2) {
229         switch (AA.alias(MemoryLocation::get(cast<LoadInst>(*I1)),
230                          MemoryLocation::get(cast<StoreInst>(*I2)))) {
231         case NoAlias:
232           PrintLoadStoreResults("NoAlias", PrintNoAlias, *I1, *I2,
233                                 F.getParent());
234           ++NoAliasCount;
235           break;
236         case MayAlias:
237           PrintLoadStoreResults("MayAlias", PrintMayAlias, *I1, *I2,
238                                 F.getParent());
239           ++MayAliasCount;
240           break;
241         case PartialAlias:
242           PrintLoadStoreResults("PartialAlias", PrintPartialAlias, *I1, *I2,
243                                 F.getParent());
244           ++PartialAliasCount;
245           break;
246         case MustAlias:
247           PrintLoadStoreResults("MustAlias", PrintMustAlias, *I1, *I2,
248                                 F.getParent());
249           ++MustAliasCount;
250           break;
251         }
252       }
253     }
254 
255     // iterate over all pairs of store, store
256     for (SetVector<Value *>::iterator I1 = Stores.begin(), E = Stores.end();
257          I1 != E; ++I1) {
258       for (SetVector<Value *>::iterator I2 = Stores.begin(); I2 != I1; ++I2) {
259         switch (AA.alias(MemoryLocation::get(cast<StoreInst>(*I1)),
260                          MemoryLocation::get(cast<StoreInst>(*I2)))) {
261         case NoAlias:
262           PrintLoadStoreResults("NoAlias", PrintNoAlias, *I1, *I2,
263                                 F.getParent());
264           ++NoAliasCount;
265           break;
266         case MayAlias:
267           PrintLoadStoreResults("MayAlias", PrintMayAlias, *I1, *I2,
268                                 F.getParent());
269           ++MayAliasCount;
270           break;
271         case PartialAlias:
272           PrintLoadStoreResults("PartialAlias", PrintPartialAlias, *I1, *I2,
273                                 F.getParent());
274           ++PartialAliasCount;
275           break;
276         case MustAlias:
277           PrintLoadStoreResults("MustAlias", PrintMustAlias, *I1, *I2,
278                                 F.getParent());
279           ++MustAliasCount;
280           break;
281         }
282       }
283     }
284   }
285 
286   // Mod/ref alias analysis: compare all pairs of calls and values
287   for (auto C = CallSites.begin(), Ce = CallSites.end(); C != Ce; ++C) {
288     Instruction *I = C->getInstruction();
289 
290     for (SetVector<Value *>::iterator V = Pointers.begin(), Ve = Pointers.end();
291          V != Ve; ++V) {
292       uint64_t Size = MemoryLocation::UnknownSize;
293       Type *ElTy = cast<PointerType>((*V)->getType())->getElementType();
294       if (ElTy->isSized()) Size = DL.getTypeStoreSize(ElTy);
295 
296       switch (AA.getModRefInfo(*C, *V, Size)) {
297       case MRI_NoModRef:
298         PrintModRefResults("NoModRef", PrintNoModRef, I, *V, F.getParent());
299         ++NoModRefCount;
300         break;
301       case MRI_Mod:
302         PrintModRefResults("Just Mod", PrintMod, I, *V, F.getParent());
303         ++ModCount;
304         break;
305       case MRI_Ref:
306         PrintModRefResults("Just Ref", PrintRef, I, *V, F.getParent());
307         ++RefCount;
308         break;
309       case MRI_ModRef:
310         PrintModRefResults("Both ModRef", PrintModRef, I, *V, F.getParent());
311         ++ModRefCount;
312         break;
313       }
314     }
315   }
316 
317   // Mod/ref alias analysis: compare all pairs of calls
318   for (auto C = CallSites.begin(), Ce = CallSites.end(); C != Ce; ++C) {
319     for (auto D = CallSites.begin(); D != Ce; ++D) {
320       if (D == C)
321         continue;
322       switch (AA.getModRefInfo(*C, *D)) {
323       case MRI_NoModRef:
324         PrintModRefResults("NoModRef", PrintNoModRef, *C, *D, F.getParent());
325         ++NoModRefCount;
326         break;
327       case MRI_Mod:
328         PrintModRefResults("Just Mod", PrintMod, *C, *D, F.getParent());
329         ++ModCount;
330         break;
331       case MRI_Ref:
332         PrintModRefResults("Just Ref", PrintRef, *C, *D, F.getParent());
333         ++RefCount;
334         break;
335       case MRI_ModRef:
336         PrintModRefResults("Both ModRef", PrintModRef, *C, *D, F.getParent());
337         ++ModRefCount;
338         break;
339       }
340     }
341   }
342 
343   return false;
344 }
345 
PrintPercent(unsigned Num,unsigned Sum)346 static void PrintPercent(unsigned Num, unsigned Sum) {
347   errs() << "(" << Num*100ULL/Sum << "."
348          << ((Num*1000ULL/Sum) % 10) << "%)\n";
349 }
350 
doFinalization(Module & M)351 bool AAEval::doFinalization(Module &M) {
352   unsigned AliasSum =
353       NoAliasCount + MayAliasCount + PartialAliasCount + MustAliasCount;
354   errs() << "===== Alias Analysis Evaluator Report =====\n";
355   if (AliasSum == 0) {
356     errs() << "  Alias Analysis Evaluator Summary: No pointers!\n";
357   } else {
358     errs() << "  " << AliasSum << " Total Alias Queries Performed\n";
359     errs() << "  " << NoAliasCount << " no alias responses ";
360     PrintPercent(NoAliasCount, AliasSum);
361     errs() << "  " << MayAliasCount << " may alias responses ";
362     PrintPercent(MayAliasCount, AliasSum);
363     errs() << "  " << PartialAliasCount << " partial alias responses ";
364     PrintPercent(PartialAliasCount, AliasSum);
365     errs() << "  " << MustAliasCount << " must alias responses ";
366     PrintPercent(MustAliasCount, AliasSum);
367     errs() << "  Alias Analysis Evaluator Pointer Alias Summary: "
368            << NoAliasCount * 100 / AliasSum << "%/"
369            << MayAliasCount * 100 / AliasSum << "%/"
370            << PartialAliasCount * 100 / AliasSum << "%/"
371            << MustAliasCount * 100 / AliasSum << "%\n";
372   }
373 
374   // Display the summary for mod/ref analysis
375   unsigned ModRefSum = NoModRefCount + ModCount + RefCount + ModRefCount;
376   if (ModRefSum == 0) {
377     errs() << "  Alias Analysis Mod/Ref Evaluator Summary: no "
378               "mod/ref!\n";
379   } else {
380     errs() << "  " << ModRefSum << " Total ModRef Queries Performed\n";
381     errs() << "  " << NoModRefCount << " no mod/ref responses ";
382     PrintPercent(NoModRefCount, ModRefSum);
383     errs() << "  " << ModCount << " mod responses ";
384     PrintPercent(ModCount, ModRefSum);
385     errs() << "  " << RefCount << " ref responses ";
386     PrintPercent(RefCount, ModRefSum);
387     errs() << "  " << ModRefCount << " mod & ref responses ";
388     PrintPercent(ModRefCount, ModRefSum);
389     errs() << "  Alias Analysis Evaluator Mod/Ref Summary: "
390            << NoModRefCount * 100 / ModRefSum << "%/"
391            << ModCount * 100 / ModRefSum << "%/" << RefCount * 100 / ModRefSum
392            << "%/" << ModRefCount * 100 / ModRefSum << "%\n";
393   }
394 
395   return false;
396 }
397