1 //===- ProvenanceAnalysis.cpp - ObjC ARC Optimization ---------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
11 /// This file defines a special form of Alias Analysis called ``Provenance
12 /// Analysis''. The word ``provenance'' refers to the history of the ownership
13 /// of an object. Thus ``Provenance Analysis'' is an analysis which attempts to
14 /// use various techniques to determine if locally
16 /// WARNING: This file knows about certain library functions. It recognizes them
17 /// by name, and hardwires knowledge of their semantics.
19 /// WARNING: This file knows about how certain Objective-C library functions are
20 /// used. Naive LLVM IR transformations which would otherwise be
21 /// behavior-preserving may break these assumptions.
23 //===----------------------------------------------------------------------===//
25 #include "ProvenanceAnalysis.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/Analysis/AliasAnalysis.h"
29 #include "llvm/Analysis/ObjCARCAnalysisUtils.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/IR/Use.h"
33 #include "llvm/IR/User.h"
34 #include "llvm/IR/Value.h"
35 #include "llvm/Support/Casting.h"
39 using namespace llvm::objcarc;
41 bool ProvenanceAnalysis::relatedSelect(const SelectInst *A,
43 const DataLayout &DL = A->getModule()->getDataLayout();
44 // If the values are Selects with the same condition, we can do a more precise
45 // check: just check for relations between the values on corresponding arms.
46 if (const SelectInst *SB = dyn_cast<SelectInst>(B))
47 if (A->getCondition() == SB->getCondition())
48 return related(A->getTrueValue(), SB->getTrueValue(), DL) ||
49 related(A->getFalseValue(), SB->getFalseValue(), DL);
51 // Check both arms of the Select node individually.
52 return related(A->getTrueValue(), B, DL) ||
53 related(A->getFalseValue(), B, DL);
56 bool ProvenanceAnalysis::relatedPHI(const PHINode *A,
58 const DataLayout &DL = A->getModule()->getDataLayout();
59 // If the values are PHIs in the same block, we can do a more precise as well
60 // as efficient check: just check for relations between the values on
61 // corresponding edges.
62 if (const PHINode *PNB = dyn_cast<PHINode>(B))
63 if (PNB->getParent() == A->getParent()) {
64 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i)
65 if (related(A->getIncomingValue(i),
66 PNB->getIncomingValueForBlock(A->getIncomingBlock(i)), DL))
71 // Check each unique source of the PHI node against B.
72 SmallPtrSet<const Value *, 4> UniqueSrc;
73 for (Value *PV1 : A->incoming_values()) {
74 if (UniqueSrc.insert(PV1).second && related(PV1, B, DL))
78 // All of the arms checked out.
82 /// Test if the value of P, or any value covered by its provenance, is ever
83 /// stored within the function (not counting callees).
84 static bool IsStoredObjCPointer(const Value *P) {
85 SmallPtrSet<const Value *, 8> Visited;
86 SmallVector<const Value *, 8> Worklist;
87 Worklist.push_back(P);
90 P = Worklist.pop_back_val();
91 for (const Use &U : P->uses()) {
92 const User *Ur = U.getUser();
93 if (isa<StoreInst>(Ur)) {
94 if (U.getOperandNo() == 0)
95 // The pointer is stored.
97 // The pointed is stored through.
100 if (isa<CallInst>(Ur))
101 // The pointer is passed as an argument, ignore this.
103 if (isa<PtrToIntInst>(P))
106 if (Visited.insert(Ur).second)
107 Worklist.push_back(Ur);
109 } while (!Worklist.empty());
111 // Everything checked out.
115 bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B,
116 const DataLayout &DL) {
117 // Ask regular AliasAnalysis, for a first approximation.
118 switch (AA->alias(A, B)) {
128 bool AIsIdentified = IsObjCIdentifiedObject(A);
129 bool BIsIdentified = IsObjCIdentifiedObject(B);
131 // An ObjC-Identified object can't alias a load if it is never locally stored.
133 // Check for an obvious escape.
134 if (isa<LoadInst>(B))
135 return IsStoredObjCPointer(A);
137 // Check for an obvious escape.
138 if (isa<LoadInst>(A))
139 return IsStoredObjCPointer(B);
140 // Both pointers are identified and escapes aren't an evident problem.
143 } else if (BIsIdentified) {
144 // Check for an obvious escape.
145 if (isa<LoadInst>(A))
146 return IsStoredObjCPointer(B);
149 // Special handling for PHI and Select.
150 if (const PHINode *PN = dyn_cast<PHINode>(A))
151 return relatedPHI(PN, B);
152 if (const PHINode *PN = dyn_cast<PHINode>(B))
153 return relatedPHI(PN, A);
154 if (const SelectInst *S = dyn_cast<SelectInst>(A))
155 return relatedSelect(S, B);
156 if (const SelectInst *S = dyn_cast<SelectInst>(B))
157 return relatedSelect(S, A);
163 bool ProvenanceAnalysis::related(const Value *A, const Value *B,
164 const DataLayout &DL) {
165 A = GetUnderlyingObjCPtrCached(A, DL, UnderlyingObjCPtrCache);
166 B = GetUnderlyingObjCPtrCached(B, DL, UnderlyingObjCPtrCache);
172 // Begin by inserting a conservative value into the map. If the insertion
173 // fails, we have the answer already. If it succeeds, leave it there until we
174 // compute the real answer to guard against recursive queries.
175 if (A > B) std::swap(A, B);
176 std::pair<CachedResultsTy::iterator, bool> Pair =
177 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true));
179 return Pair.first->second;
181 bool Result = relatedCheck(A, B, DL);
182 CachedResults[ValuePairTy(A, B)] = Result;