1 //===- ProvenanceAnalysis.cpp - ObjC ARC Optimization ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
12 /// This file defines a special form of Alias Analysis called ``Provenance
13 /// Analysis''. The word ``provenance'' refers to the history of the ownership
14 /// of an object. Thus ``Provenance Analysis'' is an analysis which attempts to
15 /// use various techniques to determine if locally
17 /// WARNING: This file knows about certain library functions. It recognizes them
18 /// by name, and hardwires knowledge of their semantics.
20 /// WARNING: This file knows about how certain Objective-C library functions are
21 /// used. Naive LLVM IR transformations which would otherwise be
22 /// behavior-preserving may break these assumptions.
24 //===----------------------------------------------------------------------===//
26 #include "ProvenanceAnalysis.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/SmallVector.h"
29 #include "llvm/Analysis/AliasAnalysis.h"
30 #include "llvm/Analysis/ObjCARCAnalysisUtils.h"
31 #include "llvm/IR/Instructions.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/IR/Use.h"
34 #include "llvm/IR/User.h"
35 #include "llvm/IR/Value.h"
36 #include "llvm/Support/Casting.h"
40 using namespace llvm::objcarc;
42 bool ProvenanceAnalysis::relatedSelect(const SelectInst *A,
44 const DataLayout &DL = A->getModule()->getDataLayout();
45 // If the values are Selects with the same condition, we can do a more precise
46 // check: just check for relations between the values on corresponding arms.
47 if (const SelectInst *SB = dyn_cast<SelectInst>(B))
48 if (A->getCondition() == SB->getCondition())
49 return related(A->getTrueValue(), SB->getTrueValue(), DL) ||
50 related(A->getFalseValue(), SB->getFalseValue(), DL);
52 // Check both arms of the Select node individually.
53 return related(A->getTrueValue(), B, DL) ||
54 related(A->getFalseValue(), B, DL);
57 bool ProvenanceAnalysis::relatedPHI(const PHINode *A,
59 const DataLayout &DL = A->getModule()->getDataLayout();
60 // If the values are PHIs in the same block, we can do a more precise as well
61 // as efficient check: just check for relations between the values on
62 // corresponding edges.
63 if (const PHINode *PNB = dyn_cast<PHINode>(B))
64 if (PNB->getParent() == A->getParent()) {
65 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i)
66 if (related(A->getIncomingValue(i),
67 PNB->getIncomingValueForBlock(A->getIncomingBlock(i)), DL))
72 // Check each unique source of the PHI node against B.
73 SmallPtrSet<const Value *, 4> UniqueSrc;
74 for (Value *PV1 : A->incoming_values()) {
75 if (UniqueSrc.insert(PV1).second && related(PV1, B, DL))
79 // All of the arms checked out.
83 /// Test if the value of P, or any value covered by its provenance, is ever
84 /// stored within the function (not counting callees).
85 static bool IsStoredObjCPointer(const Value *P) {
86 SmallPtrSet<const Value *, 8> Visited;
87 SmallVector<const Value *, 8> Worklist;
88 Worklist.push_back(P);
91 P = Worklist.pop_back_val();
92 for (const Use &U : P->uses()) {
93 const User *Ur = U.getUser();
94 if (isa<StoreInst>(Ur)) {
95 if (U.getOperandNo() == 0)
96 // The pointer is stored.
98 // The pointed is stored through.
101 if (isa<CallInst>(Ur))
102 // The pointer is passed as an argument, ignore this.
104 if (isa<PtrToIntInst>(P))
107 if (Visited.insert(Ur).second)
108 Worklist.push_back(Ur);
110 } while (!Worklist.empty());
112 // Everything checked out.
116 bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B,
117 const DataLayout &DL) {
118 // Skip past provenance pass-throughs.
119 A = GetUnderlyingObjCPtr(A, DL);
120 B = GetUnderlyingObjCPtr(B, DL);
126 // Ask regular AliasAnalysis, for a first approximation.
127 switch (AA->alias(A, B)) {
137 bool AIsIdentified = IsObjCIdentifiedObject(A);
138 bool BIsIdentified = IsObjCIdentifiedObject(B);
140 // An ObjC-Identified object can't alias a load if it is never locally stored.
142 // Check for an obvious escape.
143 if (isa<LoadInst>(B))
144 return IsStoredObjCPointer(A);
146 // Check for an obvious escape.
147 if (isa<LoadInst>(A))
148 return IsStoredObjCPointer(B);
149 // Both pointers are identified and escapes aren't an evident problem.
152 } else if (BIsIdentified) {
153 // Check for an obvious escape.
154 if (isa<LoadInst>(A))
155 return IsStoredObjCPointer(B);
158 // Special handling for PHI and Select.
159 if (const PHINode *PN = dyn_cast<PHINode>(A))
160 return relatedPHI(PN, B);
161 if (const PHINode *PN = dyn_cast<PHINode>(B))
162 return relatedPHI(PN, A);
163 if (const SelectInst *S = dyn_cast<SelectInst>(A))
164 return relatedSelect(S, B);
165 if (const SelectInst *S = dyn_cast<SelectInst>(B))
166 return relatedSelect(S, A);
172 bool ProvenanceAnalysis::related(const Value *A, const Value *B,
173 const DataLayout &DL) {
174 // Begin by inserting a conservative value into the map. If the insertion
175 // fails, we have the answer already. If it succeeds, leave it there until we
176 // compute the real answer to guard against recursive queries.
177 if (A > B) std::swap(A, B);
178 std::pair<CachedResultsTy::iterator, bool> Pair =
179 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true));
181 return Pair.first->second;
183 bool Result = relatedCheck(A, B, DL);
184 CachedResults[ValuePairTy(A, B)] = Result;