AliasAnalysisEvaluator.cpp revision f5a86f45e75ec744c203270ffa03659eb0a220c1 
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/InstIterator.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/raw_ostream.h"
32#include "llvm/ADT/SetVector.h"
33using namespace llvm;
34
35static cl::opt<bool> PrintAll("print-all-alias-modref-info", cl::ReallyHidden);
36
37static cl::opt<bool> PrintNoAlias("print-no-aliases", cl::ReallyHidden);
38static cl::opt<bool> PrintMayAlias("print-may-aliases", cl::ReallyHidden);
39static cl::opt<bool> PrintMustAlias("print-must-aliases", cl::ReallyHidden);
40
41static cl::opt<bool> PrintNoModRef("print-no-modref", cl::ReallyHidden);
42static cl::opt<bool> PrintMod("print-mod", cl::ReallyHidden);
43static cl::opt<bool> PrintRef("print-ref", cl::ReallyHidden);
44static cl::opt<bool> PrintModRef("print-modref", cl::ReallyHidden);
45
46namespace {
47  class AAEval : public FunctionPass {
48    unsigned NoAlias, MayAlias, MustAlias;
49    unsigned NoModRef, Mod, Ref, ModRef;
50
51  public:
52    static char ID; // Pass identification, replacement for typeid
53    AAEval() : FunctionPass(&ID) {}
54
55    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
56      AU.addRequired<AliasAnalysis>();
57      AU.setPreservesAll();
58    }
59
60    bool doInitialization(Module &M) {
61      NoAlias = MayAlias = MustAlias = 0;
62      NoModRef = Mod = Ref = ModRef = 0;
63
64      if (PrintAll) {
65        PrintNoAlias = PrintMayAlias = PrintMustAlias = true;
66        PrintNoModRef = PrintMod = PrintRef = PrintModRef = true;
67      }
68      return false;
69    }
70
71    bool runOnFunction(Function &F);
72    bool doFinalization(Module &M);
73  };
74}
75
76char AAEval::ID = 0;
77static RegisterPass<AAEval>
78X("aa-eval", "Exhaustive Alias Analysis Precision Evaluator", false, true);
79
80FunctionPass *llvm::createAAEvalPass() { return new AAEval(); }
81
82static void PrintResults(const char *Msg, bool P, const Value *V1,
83                         const Value *V2, const Module *M) {
84  if (P) {
85    std::string o1, o2;
86    {
87      raw_string_ostream os1(o1), os2(o2);
88      WriteAsOperand(os1, V1, true, M);
89      WriteAsOperand(os2, V2, true, M);
90    }
91
92    if (o2 < o1)
93      std::swap(o1, o2);
94    errs() << "  " << Msg << ":\t"
95           << o1 << ", "
96           << o2 << "\n";
97  }
98}
99
100static inline void
101PrintModRefResults(const char *Msg, bool P, Instruction *I, Value *Ptr,
102                   Module *M) {
103  if (P) {
104    errs() << "  " << Msg << ":  Ptr: ";
105    WriteAsOperand(errs(), Ptr, true, M);
106    errs() << "\t<->" << *I << '\n';
107  }
108}
109
110bool AAEval::runOnFunction(Function &F) {
111  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
112
113  SetVector<Value *> Pointers;
114  SetVector<CallSite> CallSites;
115
116  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
117    if (isa<PointerType>(I->getType()))    // Add all pointer arguments
118      Pointers.insert(I);
119
120  for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
121    if (isa<PointerType>(I->getType())) // Add all pointer instructions
122      Pointers.insert(&*I);
123    Instruction &Inst = *I;
124    User::op_iterator OI = Inst.op_begin();
125    CallSite CS = CallSite::get(&Inst);
126    if (CS.getInstruction() &&
127        isa<Function>(CS.getCalledValue()))
128      ++OI;  // Skip actual functions for direct function calls.
129    for (; OI != Inst.op_end(); ++OI)
130      if (isa<PointerType>((*OI)->getType()) && !isa<ConstantPointerNull>(*OI))
131        Pointers.insert(*OI);
132
133    if (CS.getInstruction()) CallSites.insert(CS);
134  }
135
136  if (PrintNoAlias || PrintMayAlias || PrintMustAlias ||
137      PrintNoModRef || PrintMod || PrintRef || PrintModRef)
138    errs() << "Function: " << F.getName() << ": " << Pointers.size()
139           << " pointers, " << CallSites.size() << " call sites\n";
140
141  // iterate over the worklist, and run the full (n^2)/2 disambiguations
142  for (SetVector<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
143       I1 != E; ++I1) {
144    unsigned I1Size = ~0u;
145    const Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
146    if (I1ElTy->isSized()) I1Size = AA.getTypeStoreSize(I1ElTy);
147
148    for (SetVector<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
149      unsigned I2Size = ~0u;
150      const Type *I2ElTy =cast<PointerType>((*I2)->getType())->getElementType();
151      if (I2ElTy->isSized()) I2Size = AA.getTypeStoreSize(I2ElTy);
152
153      switch (AA.alias(*I1, I1Size, *I2, I2Size)) {
154      case AliasAnalysis::NoAlias:
155        PrintResults("NoAlias", PrintNoAlias, *I1, *I2, F.getParent());
156        ++NoAlias; break;
157      case AliasAnalysis::MayAlias:
158        PrintResults("MayAlias", PrintMayAlias, *I1, *I2, F.getParent());
159        ++MayAlias; break;
160      case AliasAnalysis::MustAlias:
161        PrintResults("MustAlias", PrintMustAlias, *I1, *I2, F.getParent());
162        ++MustAlias; break;
163      default:
164        errs() << "Unknown alias query result!\n";
165      }
166    }
167  }
168
169  // Mod/ref alias analysis: compare all pairs of calls and values
170  for (SetVector<CallSite>::iterator C = CallSites.begin(),
171         Ce = CallSites.end(); C != Ce; ++C) {
172    Instruction *I = C->getInstruction();
173
174    for (SetVector<Value *>::iterator V = Pointers.begin(), Ve = Pointers.end();
175         V != Ve; ++V) {
176      unsigned Size = ~0u;
177      const Type *ElTy = cast<PointerType>((*V)->getType())->getElementType();
178      if (ElTy->isSized()) Size = AA.getTypeStoreSize(ElTy);
179
180      switch (AA.getModRefInfo(*C, *V, Size)) {
181      case AliasAnalysis::NoModRef:
182        PrintModRefResults("NoModRef", PrintNoModRef, I, *V, F.getParent());
183        ++NoModRef; break;
184      case AliasAnalysis::Mod:
185        PrintModRefResults("     Mod", PrintMod, I, *V, F.getParent());
186        ++Mod; break;
187      case AliasAnalysis::Ref:
188        PrintModRefResults("     Ref", PrintRef, I, *V, F.getParent());
189        ++Ref; break;
190      case AliasAnalysis::ModRef:
191        PrintModRefResults("  ModRef", PrintModRef, I, *V, F.getParent());
192        ++ModRef; break;
193      default:
194        errs() << "Unknown alias query result!\n";
195      }
196    }
197  }
198
199  return false;
200}
201
202static void PrintPercent(unsigned Num, unsigned Sum) {
203  errs() << "(" << Num*100ULL/Sum << "."
204         << ((Num*1000ULL/Sum) % 10) << "%)\n";
205}
206
207bool AAEval::doFinalization(Module &M) {
208  unsigned AliasSum = NoAlias + MayAlias + MustAlias;
209  errs() << "===== Alias Analysis Evaluator Report =====\n";
210  if (AliasSum == 0) {
211    errs() << "  Alias Analysis Evaluator Summary: No pointers!\n";
212  } else {
213    errs() << "  " << AliasSum << " Total Alias Queries Performed\n";
214    errs() << "  " << NoAlias << " no alias responses ";
215    PrintPercent(NoAlias, AliasSum);
216    errs() << "  " << MayAlias << " may alias responses ";
217    PrintPercent(MayAlias, AliasSum);
218    errs() << "  " << MustAlias << " must alias responses ";
219    PrintPercent(MustAlias, AliasSum);
220    errs() << "  Alias Analysis Evaluator Pointer Alias Summary: "
221           << NoAlias*100/AliasSum  << "%/" << MayAlias*100/AliasSum << "%/"
222           << MustAlias*100/AliasSum << "%\n";
223  }
224
225  // Display the summary for mod/ref analysis
226  unsigned ModRefSum = NoModRef + Mod + Ref + ModRef;
227  if (ModRefSum == 0) {
228    errs() << "  Alias Analysis Mod/Ref Evaluator Summary: no mod/ref!\n";
229  } else {
230    errs() << "  " << ModRefSum << " Total ModRef Queries Performed\n";
231    errs() << "  " << NoModRef << " no mod/ref responses ";
232    PrintPercent(NoModRef, ModRefSum);
233    errs() << "  " << Mod << " mod responses ";
234    PrintPercent(Mod, ModRefSum);
235    errs() << "  " << Ref << " ref responses ";
236    PrintPercent(Ref, ModRefSum);
237    errs() << "  " << ModRef << " mod & ref responses ";
238    PrintPercent(ModRef, ModRefSum);
239    errs() << "  Alias Analysis Evaluator Mod/Ref Summary: "
240           << NoModRef*100/ModRefSum  << "%/" << Mod*100/ModRefSum << "%/"
241           << Ref*100/ModRefSum << "%/" << ModRef*100/ModRefSum << "%\n";
242  }
243
244  return false;
245}
246