AliasAnalysisEvaluator.cpp revision 791102fb1192ac9483274e54cbc42480c9b1af10 
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/Compiler.h"
32#include "llvm/Support/raw_ostream.h"
33#include <set>
34#include <sstream>
35using namespace llvm;
36
37static cl::opt<bool> PrintAll("print-all-alias-modref-info", cl::ReallyHidden);
38
39static cl::opt<bool> PrintNoAlias("print-no-aliases", cl::ReallyHidden);
40static cl::opt<bool> PrintMayAlias("print-may-aliases", cl::ReallyHidden);
41static cl::opt<bool> PrintMustAlias("print-must-aliases", cl::ReallyHidden);
42
43static cl::opt<bool> PrintNoModRef("print-no-modref", cl::ReallyHidden);
44static cl::opt<bool> PrintMod("print-mod", cl::ReallyHidden);
45static cl::opt<bool> PrintRef("print-ref", cl::ReallyHidden);
46static cl::opt<bool> PrintModRef("print-modref", cl::ReallyHidden);
47
48namespace {
49  class VISIBILITY_HIDDEN AAEval : public FunctionPass {
50    unsigned NoAlias, MayAlias, MustAlias;
51    unsigned NoModRef, Mod, Ref, ModRef;
52
53  public:
54    static char ID; // Pass identification, replacement for typeid
55    AAEval() : FunctionPass(&ID) {}
56
57    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
58      AU.addRequired<AliasAnalysis>();
59      AU.setPreservesAll();
60    }
61
62    bool doInitialization(Module &M) {
63      NoAlias = MayAlias = MustAlias = 0;
64      NoModRef = Mod = Ref = ModRef = 0;
65
66      if (PrintAll) {
67        PrintNoAlias = PrintMayAlias = PrintMustAlias = true;
68        PrintNoModRef = PrintMod = PrintRef = PrintModRef = true;
69      }
70      return false;
71    }
72
73    bool runOnFunction(Function &F);
74    bool doFinalization(Module &M);
75  };
76}
77
78char AAEval::ID = 0;
79static RegisterPass<AAEval>
80X("aa-eval", "Exhaustive Alias Analysis Precision Evaluator", false, true);
81
82FunctionPass *llvm::createAAEvalPass() { return new AAEval(); }
83
84static void PrintResults(const char *Msg, bool P, const Value *V1,
85                         const Value *V2, const Module *M) {
86  if (P) {
87    std::string o1, o2;
88    {
89      raw_string_ostream os1(o1), os2(o2);
90      WriteAsOperand(os1, V1, true, M);
91      WriteAsOperand(os2, V2, true, M);
92    }
93
94    if (o2 < o1)
95      std::swap(o1, o2);
96    errs() << "  " << Msg << ":\t"
97           << o1 << ", "
98           << o2 << "\n";
99  }
100}
101
102static inline void
103PrintModRefResults(const char *Msg, bool P, Instruction *I, Value *Ptr,
104                   Module *M) {
105  if (P) {
106    errs() << "  " << Msg << ":  Ptr: ";
107    WriteAsOperand(errs(), Ptr, true, M);
108    errs() << "\t<->" << *I;
109  }
110}
111
112bool AAEval::runOnFunction(Function &F) {
113  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
114
115  std::set<Value *> Pointers;
116  std::set<CallSite> CallSites;
117
118  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
119    if (isa<PointerType>(I->getType()))    // Add all pointer arguments
120      Pointers.insert(I);
121
122  for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
123    if (isa<PointerType>(I->getType())) // Add all pointer instructions
124      Pointers.insert(&*I);
125    Instruction &Inst = *I;
126    User::op_iterator OI = Inst.op_begin();
127    CallSite CS = CallSite::get(&Inst);
128    if (CS.getInstruction() &&
129        isa<Function>(CS.getCalledValue()))
130      ++OI;  // Skip actual functions for direct function calls.
131    for (; OI != Inst.op_end(); ++OI)
132      if (isa<PointerType>((*OI)->getType()) && !isa<ConstantPointerNull>(*OI))
133        Pointers.insert(*OI);
134
135    if (CS.getInstruction()) CallSites.insert(CS);
136  }
137
138  if (PrintNoAlias || PrintMayAlias || PrintMustAlias ||
139      PrintNoModRef || PrintMod || PrintRef || PrintModRef)
140    errs() << "Function: " << F.getName() << ": " << Pointers.size()
141           << " pointers, " << CallSites.size() << " call sites\n";
142
143  // iterate over the worklist, and run the full (n^2)/2 disambiguations
144  for (std::set<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
145       I1 != E; ++I1) {
146    unsigned I1Size = ~0u;
147    const Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
148    if (I1ElTy->isSized()) I1Size = AA.getTypeStoreSize(I1ElTy);
149
150    for (std::set<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
151      unsigned I2Size = ~0u;
152      const Type *I2ElTy =cast<PointerType>((*I2)->getType())->getElementType();
153      if (I2ElTy->isSized()) I2Size = AA.getTypeStoreSize(I2ElTy);
154
155      switch (AA.alias(*I1, I1Size, *I2, I2Size)) {
156      case AliasAnalysis::NoAlias:
157        PrintResults("NoAlias", PrintNoAlias, *I1, *I2, F.getParent());
158        ++NoAlias; break;
159      case AliasAnalysis::MayAlias:
160        PrintResults("MayAlias", PrintMayAlias, *I1, *I2, F.getParent());
161        ++MayAlias; break;
162      case AliasAnalysis::MustAlias:
163        PrintResults("MustAlias", PrintMustAlias, *I1, *I2, F.getParent());
164        ++MustAlias; break;
165      default:
166        errs() << "Unknown alias query result!\n";
167      }
168    }
169  }
170
171  // Mod/ref alias analysis: compare all pairs of calls and values
172  for (std::set<CallSite>::iterator C = CallSites.begin(),
173         Ce = CallSites.end(); C != Ce; ++C) {
174    Instruction *I = C->getInstruction();
175
176    for (std::set<Value *>::iterator V = Pointers.begin(), Ve = Pointers.end();
177         V != Ve; ++V) {
178      unsigned Size = ~0u;
179      const Type *ElTy = cast<PointerType>((*V)->getType())->getElementType();
180      if (ElTy->isSized()) Size = AA.getTypeStoreSize(ElTy);
181
182      switch (AA.getModRefInfo(*C, *V, Size)) {
183      case AliasAnalysis::NoModRef:
184        PrintModRefResults("NoModRef", PrintNoModRef, I, *V, F.getParent());
185        ++NoModRef; break;
186      case AliasAnalysis::Mod:
187        PrintModRefResults("     Mod", PrintMod, I, *V, F.getParent());
188        ++Mod; break;
189      case AliasAnalysis::Ref:
190        PrintModRefResults("     Ref", PrintRef, I, *V, F.getParent());
191        ++Ref; break;
192      case AliasAnalysis::ModRef:
193        PrintModRefResults("  ModRef", PrintModRef, I, *V, F.getParent());
194        ++ModRef; break;
195      default:
196        errs() << "Unknown alias query result!\n";
197      }
198    }
199  }
200
201  return false;
202}
203
204static void PrintPercent(unsigned Num, unsigned Sum) {
205  errs() << "(" << Num*100ULL/Sum << "."
206         << ((Num*1000ULL/Sum) % 10) << "%)\n";
207}
208
209bool AAEval::doFinalization(Module &M) {
210  unsigned AliasSum = NoAlias + MayAlias + MustAlias;
211  errs() << "===== Alias Analysis Evaluator Report =====\n";
212  if (AliasSum == 0) {
213    errs() << "  Alias Analysis Evaluator Summary: No pointers!\n";
214  } else {
215    errs() << "  " << AliasSum << " Total Alias Queries Performed\n";
216    errs() << "  " << NoAlias << " no alias responses ";
217    PrintPercent(NoAlias, AliasSum);
218    errs() << "  " << MayAlias << " may alias responses ";
219    PrintPercent(MayAlias, AliasSum);
220    errs() << "  " << MustAlias << " must alias responses ";
221    PrintPercent(MustAlias, AliasSum);
222    errs() << "  Alias Analysis Evaluator Pointer Alias Summary: "
223           << NoAlias*100/AliasSum  << "%/" << MayAlias*100/AliasSum << "%/"
224           << MustAlias*100/AliasSum << "%\n";
225  }
226
227  // Display the summary for mod/ref analysis
228  unsigned ModRefSum = NoModRef + Mod + Ref + ModRef;
229  if (ModRefSum == 0) {
230    errs() << "  Alias Analysis Mod/Ref Evaluator Summary: no mod/ref!\n";
231  } else {
232    errs() << "  " << ModRefSum << " Total ModRef Queries Performed\n";
233    errs() << "  " << NoModRef << " no mod/ref responses ";
234    PrintPercent(NoModRef, ModRefSum);
235    errs() << "  " << Mod << " mod responses ";
236    PrintPercent(Mod, ModRefSum);
237    errs() << "  " << Ref << " ref responses ";
238    PrintPercent(Ref, ModRefSum);
239    errs() << "  " << ModRef << " mod & ref responses ";
240    PrintPercent(ModRef, ModRefSum);
241    errs() << "  Alias Analysis Evaluator Mod/Ref Summary: "
242           << NoModRef*100/ModRefSum  << "%/" << Mod*100/ModRefSum << "%/"
243           << Ref*100/ModRefSum << "%/" << ModRef*100/ModRefSum << "%\n";
244  }
245
246  return false;
247}
248