1 //===- ObjCARCAliasAnalysis.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 //===----------------------------------------------------------------------===//
10 /// This file defines a simple ARC-aware AliasAnalysis using special knowledge
11 /// of Objective C to enhance other optimization passes which rely on the Alias
12 /// Analysis infrastructure.
14 /// WARNING: This file knows about certain library functions. It recognizes them
15 /// by name, and hardwires knowledge of their semantics.
17 /// WARNING: This file knows about how certain Objective-C library functions are
18 /// used. Naive LLVM IR transformations which would otherwise be
19 /// behavior-preserving may break these assumptions.
21 //===----------------------------------------------------------------------===//
24 #include "ObjCARCAliasAnalysis.h"
25 #include "llvm/IR/Instruction.h"
26 #include "llvm/InitializePasses.h"
27 #include "llvm/PassAnalysisSupport.h"
28 #include "llvm/PassSupport.h"
30 #define DEBUG_TYPE "objc-arc-aa"
38 using namespace llvm::objcarc;
40 // Register this pass...
41 char ObjCARCAliasAnalysis::ID = 0;
42 INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
43 "ObjC-ARC-Based Alias Analysis", false, true, false)
45 ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
46 return new ObjCARCAliasAnalysis();
50 ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
52 AliasAnalysis::getAnalysisUsage(AU);
55 AliasAnalysis::AliasResult
56 ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) {
58 return AliasAnalysis::alias(LocA, LocB);
60 // First, strip off no-ops, including ObjC-specific no-ops, and try making a
61 // precise alias query.
62 const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr);
63 const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr);
65 AliasAnalysis::alias(Location(SA, LocA.Size, LocA.AATags),
66 Location(SB, LocB.Size, LocB.AATags));
67 if (Result != MayAlias)
70 // If that failed, climb to the underlying object, including climbing through
71 // ObjC-specific no-ops, and try making an imprecise alias query.
72 const Value *UA = GetUnderlyingObjCPtr(SA);
73 const Value *UB = GetUnderlyingObjCPtr(SB);
74 if (UA != SA || UB != SB) {
75 Result = AliasAnalysis::alias(Location(UA), Location(UB));
76 // We can't use MustAlias or PartialAlias results here because
77 // GetUnderlyingObjCPtr may return an offsetted pointer value.
78 if (Result == NoAlias)
82 // If that failed, fail. We don't need to chain here, since that's covered
83 // by the earlier precise query.
88 ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc,
91 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
93 // First, strip off no-ops, including ObjC-specific no-ops, and try making
94 // a precise alias query.
95 const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr);
96 if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.AATags),
100 // If that failed, climb to the underlying object, including climbing through
101 // ObjC-specific no-ops, and try making an imprecise alias query.
102 const Value *U = GetUnderlyingObjCPtr(S);
104 return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal);
106 // If that failed, fail. We don't need to chain here, since that's covered
107 // by the earlier precise query.
111 AliasAnalysis::ModRefBehavior
112 ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
113 // We have nothing to do. Just chain to the next AliasAnalysis.
114 return AliasAnalysis::getModRefBehavior(CS);
117 AliasAnalysis::ModRefBehavior
118 ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
120 return AliasAnalysis::getModRefBehavior(F);
122 switch (GetFunctionClass(F)) {
124 return DoesNotAccessMemory;
129 return AliasAnalysis::getModRefBehavior(F);
132 AliasAnalysis::ModRefResult
133 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
135 return AliasAnalysis::getModRefInfo(CS, Loc);
137 switch (GetBasicInstructionClass(CS.getInstruction())) {
141 case IC_AutoreleaseRV:
143 case IC_AutoreleasepoolPush:
144 case IC_FusedRetainAutorelease:
145 case IC_FusedRetainAutoreleaseRV:
146 // These functions don't access any memory visible to the compiler.
147 // Note that this doesn't include objc_retainBlock, because it updates
148 // pointers when it copies block data.
154 return AliasAnalysis::getModRefInfo(CS, Loc);
157 AliasAnalysis::ModRefResult
158 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
159 ImmutableCallSite CS2) {
160 // TODO: Theoretically we could check for dependencies between objc_* calls
161 // and OnlyAccessesArgumentPointees calls or other well-behaved calls.
162 return AliasAnalysis::getModRefInfo(CS1, CS2);