1//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the ScopedNoAlias alias-analysis pass, which implements
11// metadata-based scoped no-alias support.
12//
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.
17//
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" }
21//
22// Loads and stores can be tagged with an alias-analysis scope, and also, with
23// a noalias tag for a specific scope:
24//
25// ... = load %ptr1, !alias.scope !{ !scope1 }
26// ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 }
27//
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 a superset of the alias
30// scopes in that domain of some other instruction, then the two memory
31// accesses are assumed not to alias.
32//
33//===----------------------------------------------------------------------===//
34
35#include "llvm/Analysis/ScopedNoAliasAA.h"
36#include "llvm/ADT/SmallPtrSet.h"
37#include "llvm/Analysis/TargetLibraryInfo.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"
44
45using namespace llvm;
46
47// A handy option for disabling scoped no-alias functionality. The same effect
48// can also be achieved by stripping the associated metadata tags from IR, but
49// this option is sometimes more convenient.
50static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias",
51                                         cl::init(true));
52
53namespace {
54/// AliasScopeNode - This is a simple wrapper around an MDNode which provides
55/// a higher-level interface by hiding the details of how alias analysis
56/// information is encoded in its operands.
57class AliasScopeNode {
58  const MDNode *Node;
59
60public:
61  AliasScopeNode() : Node(nullptr) {}
62  explicit AliasScopeNode(const MDNode *N) : Node(N) {}
63
64  /// getNode - Get the MDNode for this AliasScopeNode.
65  const MDNode *getNode() const { return Node; }
66
67  /// getDomain - Get the MDNode for this AliasScopeNode's domain.
68  const MDNode *getDomain() const {
69    if (Node->getNumOperands() < 2)
70      return nullptr;
71    return dyn_cast_or_null<MDNode>(Node->getOperand(1));
72  }
73};
74} // end of anonymous namespace
75
76AliasResult ScopedNoAliasAAResult::alias(const MemoryLocation &LocA,
77                                         const MemoryLocation &LocB) {
78  if (!EnableScopedNoAlias)
79    return AAResultBase::alias(LocA, LocB);
80
81  // Get the attached MDNodes.
82  const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope;
83
84  const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias;
85
86  if (!mayAliasInScopes(AScopes, BNoAlias))
87    return NoAlias;
88
89  if (!mayAliasInScopes(BScopes, ANoAlias))
90    return NoAlias;
91
92  // If they may alias, chain to the next AliasAnalysis.
93  return AAResultBase::alias(LocA, LocB);
94}
95
96ModRefInfo ScopedNoAliasAAResult::getModRefInfo(ImmutableCallSite CS,
97                                                const MemoryLocation &Loc) {
98  if (!EnableScopedNoAlias)
99    return AAResultBase::getModRefInfo(CS, Loc);
100
101  if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata(
102                                              LLVMContext::MD_noalias)))
103    return MRI_NoModRef;
104
105  if (!mayAliasInScopes(
106          CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
107          Loc.AATags.NoAlias))
108    return MRI_NoModRef;
109
110  return AAResultBase::getModRefInfo(CS, Loc);
111}
112
113ModRefInfo ScopedNoAliasAAResult::getModRefInfo(ImmutableCallSite CS1,
114                                                ImmutableCallSite CS2) {
115  if (!EnableScopedNoAlias)
116    return AAResultBase::getModRefInfo(CS1, CS2);
117
118  if (!mayAliasInScopes(
119          CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
120          CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
121    return MRI_NoModRef;
122
123  if (!mayAliasInScopes(
124          CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
125          CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
126    return MRI_NoModRef;
127
128  return AAResultBase::getModRefInfo(CS1, CS2);
129}
130
131void ScopedNoAliasAAResult::collectMDInDomain(
132    const MDNode *List, const MDNode *Domain,
133    SmallPtrSetImpl<const MDNode *> &Nodes) const {
134  for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i)
135    if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i)))
136      if (AliasScopeNode(MD).getDomain() == Domain)
137        Nodes.insert(MD);
138}
139
140bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes,
141                                             const MDNode *NoAlias) const {
142  if (!Scopes || !NoAlias)
143    return true;
144
145  // Collect the set of scope domains relevant to the noalias scopes.
146  SmallPtrSet<const MDNode *, 16> Domains;
147  for (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i)
148    if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i)))
149      if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())
150        Domains.insert(Domain);
151
152  // We alias unless, for some domain, the set of noalias scopes in that domain
153  // is a superset of the set of alias scopes in that domain.
154  for (const MDNode *Domain : Domains) {
155    SmallPtrSet<const MDNode *, 16> NANodes, ScopeNodes;
156    collectMDInDomain(NoAlias, Domain, NANodes);
157    collectMDInDomain(Scopes, Domain, ScopeNodes);
158    if (!ScopeNodes.size())
159      continue;
160
161    // To not alias, all of the nodes in ScopeNodes must be in NANodes.
162    bool FoundAll = true;
163    for (const MDNode *SMD : ScopeNodes)
164      if (!NANodes.count(SMD)) {
165        FoundAll = false;
166        break;
167      }
168
169    if (FoundAll)
170      return false;
171  }
172
173  return true;
174}
175
176ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F,
177                                           AnalysisManager<Function> *AM) {
178  return ScopedNoAliasAAResult(AM->getResult<TargetLibraryAnalysis>(F));
179}
180
181char ScopedNoAliasAA::PassID;
182
183char ScopedNoAliasAAWrapperPass::ID = 0;
184INITIALIZE_PASS_BEGIN(ScopedNoAliasAAWrapperPass, "scoped-noalias",
185                      "Scoped NoAlias Alias Analysis", false, true)
186INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
187INITIALIZE_PASS_END(ScopedNoAliasAAWrapperPass, "scoped-noalias",
188                    "Scoped NoAlias Alias Analysis", false, true)
189
190ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() {
191  return new ScopedNoAliasAAWrapperPass();
192}
193
194ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) {
195  initializeScopedNoAliasAAWrapperPassPass(*PassRegistry::getPassRegistry());
196}
197
198bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) {
199  Result.reset(new ScopedNoAliasAAResult(
200      getAnalysis<TargetLibraryInfoWrapperPass>().getTLI()));
201  return false;
202}
203
204bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) {
205  Result.reset();
206  return false;
207}
208
209void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
210  AU.setPreservesAll();
211  AU.addRequired<TargetLibraryInfoWrapperPass>();
212}
213