1 //===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
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 the ScopedNoAlias alias-analysis pass, which implements
11 // metadata-based scoped no-alias support.
13 // Alias-analysis scopes are defined by an id (which can be a string or some
14 // other metadata node), a domain node, and an optional descriptive string.
15 // A domain is defined by an id (which can be a string or some other metadata
16 // node), and an optional descriptive string.
18 // !dom0 = metadata !{ metadata !"domain of foo()" }
19 // !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" }
20 // !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" }
22 // Loads and stores can be tagged with an alias-analysis scope, and also, with
23 // a noalias tag for a specific scope:
25 // ... = load %ptr1, !alias.scope !{ !scope1 }
26 // ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 }
28 // When evaluating an aliasing query, if one of the instructions is associated
29 // has a set of noalias scopes in some domain that is superset of the alias
30 // scopes in that domain of some other instruction, then the two memory
31 // accesses are assumed not to alias.
33 //===----------------------------------------------------------------------===//
35 #include "llvm/Analysis/ScopedNoAliasAA.h"
36 #include "llvm/ADT/SmallPtrSet.h"
37 #include "llvm/Analysis/AliasAnalysis.h"
38 #include "llvm/IR/Constants.h"
39 #include "llvm/IR/LLVMContext.h"
40 #include "llvm/IR/Metadata.h"
41 #include "llvm/IR/Module.h"
42 #include "llvm/Pass.h"
43 #include "llvm/Support/CommandLine.h"
46 // A handy option for disabling scoped no-alias functionality. The same effect
47 // can also be achieved by stripping the associated metadata tags from IR, but
48 // this option is sometimes more convenient.
49 static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias",
53 /// AliasScopeNode - This is a simple wrapper around an MDNode which provides
54 /// a higher-level interface by hiding the details of how alias analysis
55 /// information is encoded in its operands.
56 class AliasScopeNode {
60 AliasScopeNode() : Node(0) {}
61 explicit AliasScopeNode(const MDNode *N) : Node(N) {}
63 /// getNode - Get the MDNode for this AliasScopeNode.
64 const MDNode *getNode() const { return Node; }
66 /// getDomain - Get the MDNode for this AliasScopeNode's domain.
67 const MDNode *getDomain() const {
68 if (Node->getNumOperands() < 2)
70 return dyn_cast_or_null<MDNode>(Node->getOperand(1));
73 } // End of anonymous namespace
75 // Register this pass...
76 char ScopedNoAliasAA::ID = 0;
77 INITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias",
78 "Scoped NoAlias Alias Analysis", false, true, false)
80 ImmutablePass *llvm::createScopedNoAliasAAPass() {
81 return new ScopedNoAliasAA();
84 bool ScopedNoAliasAA::doInitialization(Module &M) {
85 InitializeAliasAnalysis(this, &M.getDataLayout());
89 void ScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const {
91 AliasAnalysis::getAnalysisUsage(AU);
94 void ScopedNoAliasAA::collectMDInDomain(
95 const MDNode *List, const MDNode *Domain,
96 SmallPtrSetImpl<const MDNode *> &Nodes) const {
97 for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i)
98 if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i)))
99 if (AliasScopeNode(MD).getDomain() == Domain)
103 bool ScopedNoAliasAA::mayAliasInScopes(const MDNode *Scopes,
104 const MDNode *NoAlias) const {
105 if (!Scopes || !NoAlias)
108 // Collect the set of scope domains relevant to the noalias scopes.
109 SmallPtrSet<const MDNode *, 16> Domains;
110 for (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i)
111 if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i)))
112 if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())
113 Domains.insert(Domain);
115 // We alias unless, for some domain, the set of noalias scopes in that domain
116 // is a superset of the set of alias scopes in that domain.
117 for (const MDNode *Domain : Domains) {
118 SmallPtrSet<const MDNode *, 16> NANodes, ScopeNodes;
119 collectMDInDomain(NoAlias, Domain, NANodes);
120 collectMDInDomain(Scopes, Domain, ScopeNodes);
121 if (!ScopeNodes.size())
124 // To not alias, all of the nodes in ScopeNodes must be in NANodes.
125 bool FoundAll = true;
126 for (const MDNode *SMD : ScopeNodes)
127 if (!NANodes.count(SMD)) {
139 AliasResult ScopedNoAliasAA::alias(const MemoryLocation &LocA,
140 const MemoryLocation &LocB) {
141 if (!EnableScopedNoAlias)
142 return AliasAnalysis::alias(LocA, LocB);
144 // Get the attached MDNodes.
145 const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope;
147 const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias;
149 if (!mayAliasInScopes(AScopes, BNoAlias))
152 if (!mayAliasInScopes(BScopes, ANoAlias))
155 // If they may alias, chain to the next AliasAnalysis.
156 return AliasAnalysis::alias(LocA, LocB);
159 bool ScopedNoAliasAA::pointsToConstantMemory(const MemoryLocation &Loc,
161 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
164 FunctionModRefBehavior
165 ScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) {
166 return AliasAnalysis::getModRefBehavior(CS);
169 FunctionModRefBehavior ScopedNoAliasAA::getModRefBehavior(const Function *F) {
170 return AliasAnalysis::getModRefBehavior(F);
173 ModRefInfo ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS,
174 const MemoryLocation &Loc) {
175 if (!EnableScopedNoAlias)
176 return AliasAnalysis::getModRefInfo(CS, Loc);
178 if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata(
179 LLVMContext::MD_noalias)))
182 if (!mayAliasInScopes(
183 CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
187 return AliasAnalysis::getModRefInfo(CS, Loc);
190 ModRefInfo ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1,
191 ImmutableCallSite CS2) {
192 if (!EnableScopedNoAlias)
193 return AliasAnalysis::getModRefInfo(CS1, CS2);
195 if (!mayAliasInScopes(
196 CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
197 CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
200 if (!mayAliasInScopes(
201 CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
202 CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
205 return AliasAnalysis::getModRefInfo(CS1, CS2);