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>
35 using namespace llvm;
36 
37 static cl::opt<bool> PrintAll("print-all-alias-modref-info", cl::ReallyHidden);
38 
39 static cl::opt<bool> PrintNoAlias("print-no-aliases", cl::ReallyHidden);
40 static cl::opt<bool> PrintMayAlias("print-may-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 namespace {
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 
78 char AAEval::ID = 0;
79 static RegisterPass<AAEval>
80 X("aa-eval", "Exhaustive Alias Analysis Precision Evaluator", false, true);
81 
82 FunctionPass *llvm::createAAEvalPass() { return new AAEval(); }
83 
84 static void PrintResults(const char *Msg, bool P, const Value *V1, const Value *V2,
85                          const Module *M) {
86   if (P) {
87     std::stringstream s1, s2;
88     WriteAsOperand(s1, V1, true, M);
89     WriteAsOperand(s2, V2, true, M);
90     std::string o1(s1.str()), o2(s2.str());
91     if (o2 < o1)
92       std::swap(o1, o2);
93     errs() << "  " << Msg << ":\t"
94            << o1 << ", "
95            << o2 << "\n";
96   }
97 }
98 
99 static inline void
100 PrintModRefResults(const char *Msg, bool P, Instruction *I, Value *Ptr,
101                    Module *M) {
102   if (P) {
103     errs() << "  " << Msg << ":  Ptr: ";
104     WriteAsOperand(errs(), Ptr, true, M);
105     errs() << "\t<->" << *I;
106   }
107 }
108 
109 bool AAEval::runOnFunction(Function &F) {
110   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
111 
112   std::set<Value *> Pointers;
113   std::set<CallSite> CallSites;
114 
115   for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
116     if (isa<PointerType>(I->getType()))    // Add all pointer arguments
117       Pointers.insert(I);
118 
119   for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
120     if (isa<PointerType>(I->getType())) // Add all pointer instructions
121       Pointers.insert(&*I);
122     Instruction &Inst = *I;
123     User::op_iterator OI = Inst.op_begin();
124     CallSite CS = CallSite::get(&Inst);
125     if (CS.getInstruction() &&
126         isa<Function>(CS.getCalledValue()))
127       ++OI;  // Skip actual functions for direct function calls.
128     for (; OI != Inst.op_end(); ++OI)
129       if (isa<PointerType>((*OI)->getType()) && !isa<ConstantPointerNull>(*OI))
130         Pointers.insert(*OI);
131 
132     if (CS.getInstruction()) CallSites.insert(CS);
133   }
134 
135   if (PrintNoAlias || PrintMayAlias || PrintMustAlias ||
136       PrintNoModRef || PrintMod || PrintRef || PrintModRef)
137     errs() << "Function: " << F.getName() << ": " << Pointers.size()
138            << " pointers, " << CallSites.size() << " call sites\n";
139 
140   // iterate over the worklist, and run the full (n^2)/2 disambiguations
141   for (std::set<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
142        I1 != E; ++I1) {
143     unsigned I1Size = ~0u;
144     const Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
145     if (I1ElTy->isSized()) I1Size = AA.getTypeStoreSize(I1ElTy);
146 
147     for (std::set<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
148       unsigned I2Size = ~0u;
149       const Type *I2ElTy =cast<PointerType>((*I2)->getType())->getElementType();
150       if (I2ElTy->isSized()) I2Size = AA.getTypeStoreSize(I2ElTy);
151 
152       switch (AA.alias(*I1, I1Size, *I2, I2Size)) {
153       case AliasAnalysis::NoAlias:
154         PrintResults("NoAlias", PrintNoAlias, *I1, *I2, F.getParent());
155         ++NoAlias; break;
156       case AliasAnalysis::MayAlias:
157         PrintResults("MayAlias", PrintMayAlias, *I1, *I2, F.getParent());
158         ++MayAlias; break;
159       case AliasAnalysis::MustAlias:
160         PrintResults("MustAlias", PrintMustAlias, *I1, *I2, F.getParent());
161         ++MustAlias; break;
162       default:
163         errs() << "Unknown alias query result!\n";
164       }
165     }
166   }
167 
168   // Mod/ref alias analysis: compare all pairs of calls and values
169   for (std::set<CallSite>::iterator C = CallSites.begin(),
170          Ce = CallSites.end(); C != Ce; ++C) {
171     Instruction *I = C->getInstruction();
172 
173     for (std::set<Value *>::iterator V = Pointers.begin(), Ve = Pointers.end();
174          V != Ve; ++V) {
175       unsigned Size = ~0u;
176       const Type *ElTy = cast<PointerType>((*V)->getType())->getElementType();
177       if (ElTy->isSized()) Size = AA.getTypeStoreSize(ElTy);
178 
179       switch (AA.getModRefInfo(*C, *V, Size)) {
180       case AliasAnalysis::NoModRef:
181         PrintModRefResults("NoModRef", PrintNoModRef, I, *V, F.getParent());
182         ++NoModRef; break;
183       case AliasAnalysis::Mod:
184         PrintModRefResults("     Mod", PrintMod, I, *V, F.getParent());
185         ++Mod; break;
186       case AliasAnalysis::Ref:
187         PrintModRefResults("     Ref", PrintRef, I, *V, F.getParent());
188         ++Ref; break;
189       case AliasAnalysis::ModRef:
190         PrintModRefResults("  ModRef", PrintModRef, I, *V, F.getParent());
191         ++ModRef; break;
192       default:
193         errs() << "Unknown alias query result!\n";
194       }
195     }
196   }
197 
198   return false;
199 }
200 
201 static void PrintPercent(unsigned Num, unsigned Sum) {
202   errs() << "(" << Num*100ULL/Sum << "."
203          << ((Num*1000ULL/Sum) % 10) << "%)\n";
204 }
205 
206 bool AAEval::doFinalization(Module &M) {
207   unsigned AliasSum = NoAlias + MayAlias + MustAlias;
208   errs() << "===== Alias Analysis Evaluator Report =====\n";
209   if (AliasSum == 0) {
210     errs() << "  Alias Analysis Evaluator Summary: No pointers!\n";
211   } else {
212     errs() << "  " << AliasSum << " Total Alias Queries Performed\n";
213     errs() << "  " << NoAlias << " no alias responses ";
214     PrintPercent(NoAlias, AliasSum);
215     errs() << "  " << MayAlias << " may alias responses ";
216     PrintPercent(MayAlias, AliasSum);
217     errs() << "  " << MustAlias << " must alias responses ";
218     PrintPercent(MustAlias, AliasSum);
219     errs() << "  Alias Analysis Evaluator Pointer Alias Summary: "
220            << NoAlias*100/AliasSum  << "%/" << MayAlias*100/AliasSum << "%/"
221            << MustAlias*100/AliasSum << "%\n";
222   }
223 
224   // Display the summary for mod/ref analysis
225   unsigned ModRefSum = NoModRef + Mod + Ref + ModRef;
226   if (ModRefSum == 0) {
227     errs() << "  Alias Analysis Mod/Ref Evaluator Summary: no mod/ref!\n";
228   } else {
229     errs() << "  " << ModRefSum << " Total ModRef Queries Performed\n";
230     errs() << "  " << NoModRef << " no mod/ref responses ";
231     PrintPercent(NoModRef, ModRefSum);
232     errs() << "  " << Mod << " mod responses ";
233     PrintPercent(Mod, ModRefSum);
234     errs() << "  " << Ref << " ref responses ";
235     PrintPercent(Ref, ModRefSum);
236     errs() << "  " << ModRef << " mod & ref responses ";
237     PrintPercent(ModRef, ModRefSum);
238     errs() << "  Alias Analysis Evaluator Mod/Ref Summary: "
239            << NoModRef*100/ModRefSum  << "%/" << Mod*100/ModRefSum << "%/"
240            << Ref*100/ModRefSum << "%/" << ModRef*100/ModRefSum << "%\n";
241   }
242 
243   return false;
244 }
245