aboutsummaryrefslogtreecommitdiffstats
path: root/lib/Transforms/ObjCARC/ObjCARCAliasAnalysis.cpp
blob: b1515e3862077b328760a1ec98b931c4cbc7ba75 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
//===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// This file defines a simple ARC-aware AliasAnalysis using special knowledge
/// of Objective C to enhance other optimization passes which rely on the Alias
/// Analysis infrastructure.
///
/// WARNING: This file knows about certain library functions. It recognizes them
/// by name, and hardwires knowledge of their semantics.
///
/// WARNING: This file knows about how certain Objective-C library functions are
/// used. Naive LLVM IR transformations which would otherwise be
/// behavior-preserving may break these assumptions.
///
//===----------------------------------------------------------------------===//

#include "ObjCARC.h"
#include "ObjCARCAliasAnalysis.h"
#include "llvm/IR/Instruction.h"
#include "llvm/InitializePasses.h"
#include "llvm/PassAnalysisSupport.h"
#include "llvm/PassSupport.h"

#define DEBUG_TYPE "objc-arc-aa"

namespace llvm {
  class Function;
  class Value;
}

using namespace llvm;
using namespace llvm::objcarc;

// Register this pass...
char ObjCARCAliasAnalysis::ID = 0;
INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
                   "ObjC-ARC-Based Alias Analysis", false, true, false)

ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
  return new ObjCARCAliasAnalysis();
}

bool ObjCARCAliasAnalysis::doInitialization(Module &M) {
  InitializeAliasAnalysis(this, &M.getDataLayout());
  return true;
}

void
ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  AliasAnalysis::getAnalysisUsage(AU);
}

AliasAnalysis::AliasResult
ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) {
  if (!EnableARCOpts)
    return AliasAnalysis::alias(LocA, LocB);

  // First, strip off no-ops, including ObjC-specific no-ops, and try making a
  // precise alias query.
  const Value *SA = GetRCIdentityRoot(LocA.Ptr);
  const Value *SB = GetRCIdentityRoot(LocB.Ptr);
  AliasResult Result =
    AliasAnalysis::alias(Location(SA, LocA.Size, LocA.AATags),
                         Location(SB, LocB.Size, LocB.AATags));
  if (Result != MayAlias)
    return Result;

  // If that failed, climb to the underlying object, including climbing through
  // ObjC-specific no-ops, and try making an imprecise alias query.
  const Value *UA = GetUnderlyingObjCPtr(SA, *DL);
  const Value *UB = GetUnderlyingObjCPtr(SB, *DL);
  if (UA != SA || UB != SB) {
    Result = AliasAnalysis::alias(Location(UA), Location(UB));
    // We can't use MustAlias or PartialAlias results here because
    // GetUnderlyingObjCPtr may return an offsetted pointer value.
    if (Result == NoAlias)
      return NoAlias;
  }

  // If that failed, fail. We don't need to chain here, since that's covered
  // by the earlier precise query.
  return MayAlias;
}

bool
ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc,
                                             bool OrLocal) {
  if (!EnableARCOpts)
    return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);

  // First, strip off no-ops, including ObjC-specific no-ops, and try making
  // a precise alias query.
  const Value *S = GetRCIdentityRoot(Loc.Ptr);
  if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.AATags),
                                            OrLocal))
    return true;

  // If that failed, climb to the underlying object, including climbing through
  // ObjC-specific no-ops, and try making an imprecise alias query.
  const Value *U = GetUnderlyingObjCPtr(S, *DL);
  if (U != S)
    return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal);

  // If that failed, fail. We don't need to chain here, since that's covered
  // by the earlier precise query.
  return false;
}

AliasAnalysis::ModRefBehavior
ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
  // We have nothing to do. Just chain to the next AliasAnalysis.
  return AliasAnalysis::getModRefBehavior(CS);
}

AliasAnalysis::ModRefBehavior
ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
  if (!EnableARCOpts)
    return AliasAnalysis::getModRefBehavior(F);

  switch (GetFunctionClass(F)) {
  case ARCInstKind::NoopCast:
    return DoesNotAccessMemory;
  default:
    break;
  }

  return AliasAnalysis::getModRefBehavior(F);
}

AliasAnalysis::ModRefResult
ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
  if (!EnableARCOpts)
    return AliasAnalysis::getModRefInfo(CS, Loc);

  switch (GetBasicARCInstKind(CS.getInstruction())) {
  case ARCInstKind::Retain:
  case ARCInstKind::RetainRV:
  case ARCInstKind::Autorelease:
  case ARCInstKind::AutoreleaseRV:
  case ARCInstKind::NoopCast:
  case ARCInstKind::AutoreleasepoolPush:
  case ARCInstKind::FusedRetainAutorelease:
  case ARCInstKind::FusedRetainAutoreleaseRV:
    // These functions don't access any memory visible to the compiler.
    // Note that this doesn't include objc_retainBlock, because it updates
    // pointers when it copies block data.
    return NoModRef;
  default:
    break;
  }

  return AliasAnalysis::getModRefInfo(CS, Loc);
}

AliasAnalysis::ModRefResult
ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
                                    ImmutableCallSite CS2) {
  // TODO: Theoretically we could check for dependencies between objc_* calls
  // and OnlyAccessesArgumentPointees calls or other well-behaved calls.
  return AliasAnalysis::getModRefInfo(CS1, CS2);
}