AliasAnalysisEvaluator.cpp revision fcf0f082f485e45f591c0d1cbaa9a2ad8691e2c3 
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/Constants.h"
21#include "llvm/DerivedTypes.h"
22#include "llvm/Function.h"
23#include "llvm/Instructions.h"
24#include "llvm/Pass.h"
25#include "llvm/Analysis/Passes.h"
26#include "llvm/Analysis/AliasAnalysis.h"
27#include "llvm/Assembly/Writer.h"
28#include "llvm/Target/TargetData.h"
29#include "llvm/Support/Debug.h"
30#include "llvm/Support/InstIterator.h"
31#include "llvm/Support/CommandLine.h"
32#include "llvm/Support/raw_ostream.h"
33#include "llvm/ADT/SetVector.h"
34using namespace llvm;
35
36static cl::opt<bool> PrintAll("print-all-alias-modref-info", cl::ReallyHidden);
37
38static cl::opt<bool> PrintNoAlias("print-no-aliases", cl::ReallyHidden);
39static cl::opt<bool> PrintMayAlias("print-may-aliases", cl::ReallyHidden);
40static cl::opt<bool> PrintMustAlias("print-must-aliases", cl::ReallyHidden);
41
42static cl::opt<bool> PrintNoModRef("print-no-modref", cl::ReallyHidden);
43static cl::opt<bool> PrintMod("print-mod", cl::ReallyHidden);
44static cl::opt<bool> PrintRef("print-ref", cl::ReallyHidden);
45static cl::opt<bool> PrintModRef("print-modref", cl::ReallyHidden);
46
47namespace {
48  class AAEval : public FunctionPass {
49    unsigned NoAlias, MayAlias, MustAlias;
50    unsigned NoModRef, Mod, Ref, ModRef;
51
52  public:
53    static char ID; // Pass identification, replacement for typeid
54    AAEval() : FunctionPass(&ID) {}
55
56    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
57      AU.addRequired<AliasAnalysis>();
58      AU.setPreservesAll();
59    }
60
61    bool doInitialization(Module &M) {
62      NoAlias = MayAlias = MustAlias = 0;
63      NoModRef = Mod = Ref = ModRef = 0;
64
65      if (PrintAll) {
66        PrintNoAlias = PrintMayAlias = PrintMustAlias = true;
67        PrintNoModRef = PrintMod = PrintRef = PrintModRef = true;
68      }
69      return false;
70    }
71
72    bool runOnFunction(Function &F);
73    bool doFinalization(Module &M);
74  };
75}
76
77char AAEval::ID = 0;
78static RegisterPass<AAEval>
79X("aa-eval", "Exhaustive Alias Analysis Precision Evaluator", false, true);
80
81FunctionPass *llvm::createAAEvalPass() { return new AAEval(); }
82
83static void PrintResults(const char *Msg, bool P, const Value *V1,
84                         const Value *V2, const Module *M) {
85  if (P) {
86    std::string o1, o2;
87    {
88      raw_string_ostream os1(o1), os2(o2);
89      WriteAsOperand(os1, V1, true, M);
90      WriteAsOperand(os2, V2, true, M);
91    }
92
93    if (o2 < o1)
94      std::swap(o1, o2);
95    errs() << "  " << Msg << ":\t"
96           << o1 << ", "
97           << o2 << "\n";
98  }
99}
100
101static inline void
102PrintModRefResults(const char *Msg, bool P, Instruction *I, Value *Ptr,
103                   Module *M) {
104  if (P) {
105    errs() << "  " << Msg << ":  Ptr: ";
106    WriteAsOperand(errs(), Ptr, true, M);
107    errs() << "\t<->" << *I << '\n';
108  }
109}
110
111static inline bool isInterestingPointer(Value *V) {
112  return V->getType()->isPointerTy()
113      && !isa<ConstantPointerNull>(V);
114}
115
116bool AAEval::runOnFunction(Function &F) {
117  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
118
119  SetVector<Value *> Pointers;
120  SetVector<CallSite> CallSites;
121
122  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
123    if (I->getType()->isPointerTy())    // Add all pointer arguments.
124      Pointers.insert(I);
125
126  for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
127    if (I->getType()->isPointerTy()) // Add all pointer instructions.
128      Pointers.insert(&*I);
129    Instruction &Inst = *I;
130    CallSite CS = CallSite::get(&Inst);
131    if (CS) {
132      Value *Callee = CS.getCalledValue();
133      // Skip actual functions for direct function calls.
134      if (!isa<Function>(Callee) && isInterestingPointer(Callee))
135        Pointers.insert(Callee);
136      // Consider formals.
137      for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
138           AI != AE; ++AI)
139        if (isInterestingPointer(*AI))
140          Pointers.insert(*AI);
141    } else {
142      // Consider all operands.
143      for (Instruction::op_iterator OI = Inst.op_begin(), OE = Inst.op_end();
144           OI != OE; ++OI)
145        if (isInterestingPointer(*OI))
146          Pointers.insert(*OI);
147    }
148
149    if (CS.getInstruction()) CallSites.insert(CS);
150  }
151
152  if (PrintNoAlias || PrintMayAlias || PrintMustAlias ||
153      PrintNoModRef || PrintMod || PrintRef || PrintModRef)
154    errs() << "Function: " << F.getName() << ": " << Pointers.size()
155           << " pointers, " << CallSites.size() << " call sites\n";
156
157  // iterate over the worklist, and run the full (n^2)/2 disambiguations
158  for (SetVector<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
159       I1 != E; ++I1) {
160    unsigned I1Size = ~0u;
161    const Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
162    if (I1ElTy->isSized()) I1Size = AA.getTypeStoreSize(I1ElTy);
163
164    for (SetVector<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
165      unsigned I2Size = ~0u;
166      const Type *I2ElTy =cast<PointerType>((*I2)->getType())->getElementType();
167      if (I2ElTy->isSized()) I2Size = AA.getTypeStoreSize(I2ElTy);
168
169      switch (AA.alias(*I1, I1Size, *I2, I2Size)) {
170      case AliasAnalysis::NoAlias:
171        PrintResults("NoAlias", PrintNoAlias, *I1, *I2, F.getParent());
172        ++NoAlias; break;
173      case AliasAnalysis::MayAlias:
174        PrintResults("MayAlias", PrintMayAlias, *I1, *I2, F.getParent());
175        ++MayAlias; break;
176      case AliasAnalysis::MustAlias:
177        PrintResults("MustAlias", PrintMustAlias, *I1, *I2, F.getParent());
178        ++MustAlias; break;
179      default:
180        errs() << "Unknown alias query result!\n";
181      }
182    }
183  }
184
185  // Mod/ref alias analysis: compare all pairs of calls and values
186  for (SetVector<CallSite>::iterator C = CallSites.begin(),
187         Ce = CallSites.end(); C != Ce; ++C) {
188    Instruction *I = C->getInstruction();
189
190    for (SetVector<Value *>::iterator V = Pointers.begin(), Ve = Pointers.end();
191         V != Ve; ++V) {
192      unsigned Size = ~0u;
193      const Type *ElTy = cast<PointerType>((*V)->getType())->getElementType();
194      if (ElTy->isSized()) Size = AA.getTypeStoreSize(ElTy);
195
196      switch (AA.getModRefInfo(*C, *V, Size)) {
197      case AliasAnalysis::NoModRef:
198        PrintModRefResults("NoModRef", PrintNoModRef, I, *V, F.getParent());
199        ++NoModRef; break;
200      case AliasAnalysis::Mod:
201        PrintModRefResults("     Mod", PrintMod, I, *V, F.getParent());
202        ++Mod; break;
203      case AliasAnalysis::Ref:
204        PrintModRefResults("     Ref", PrintRef, I, *V, F.getParent());
205        ++Ref; break;
206      case AliasAnalysis::ModRef:
207        PrintModRefResults("  ModRef", PrintModRef, I, *V, F.getParent());
208        ++ModRef; break;
209      default:
210        errs() << "Unknown alias query result!\n";
211      }
212    }
213  }
214
215  return false;
216}
217
218static void PrintPercent(unsigned Num, unsigned Sum) {
219  errs() << "(" << Num*100ULL/Sum << "."
220         << ((Num*1000ULL/Sum) % 10) << "%)\n";
221}
222
223bool AAEval::doFinalization(Module &M) {
224  unsigned AliasSum = NoAlias + MayAlias + MustAlias;
225  errs() << "===== Alias Analysis Evaluator Report =====\n";
226  if (AliasSum == 0) {
227    errs() << "  Alias Analysis Evaluator Summary: No pointers!\n";
228  } else {
229    errs() << "  " << AliasSum << " Total Alias Queries Performed\n";
230    errs() << "  " << NoAlias << " no alias responses ";
231    PrintPercent(NoAlias, AliasSum);
232    errs() << "  " << MayAlias << " may alias responses ";
233    PrintPercent(MayAlias, AliasSum);
234    errs() << "  " << MustAlias << " must alias responses ";
235    PrintPercent(MustAlias, AliasSum);
236    errs() << "  Alias Analysis Evaluator Pointer Alias Summary: "
237           << NoAlias*100/AliasSum  << "%/" << MayAlias*100/AliasSum << "%/"
238           << MustAlias*100/AliasSum << "%\n";
239  }
240
241  // Display the summary for mod/ref analysis
242  unsigned ModRefSum = NoModRef + Mod + Ref + ModRef;
243  if (ModRefSum == 0) {
244    errs() << "  Alias Analysis Mod/Ref Evaluator Summary: no mod/ref!\n";
245  } else {
246    errs() << "  " << ModRefSum << " Total ModRef Queries Performed\n";
247    errs() << "  " << NoModRef << " no mod/ref responses ";
248    PrintPercent(NoModRef, ModRefSum);
249    errs() << "  " << Mod << " mod responses ";
250    PrintPercent(Mod, ModRefSum);
251    errs() << "  " << Ref << " ref responses ";
252    PrintPercent(Ref, ModRefSum);
253    errs() << "  " << ModRef << " mod & ref responses ";
254    PrintPercent(ModRef, ModRefSum);
255    errs() << "  Alias Analysis Evaluator Mod/Ref Summary: "
256           << NoModRef*100/ModRefSum  << "%/" << Mod*100/ModRefSum << "%/"
257           << Ref*100/ModRefSum << "%/" << ModRef*100/ModRefSum << "%\n";
258  }
259
260  return false;
261}
262