ScopedNoAliasAA.cpp revision 288943
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 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/ADT/SmallPtrSet.h" 36#include "llvm/Analysis/AliasAnalysis.h" 37#include "llvm/Analysis/Passes.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" 44using namespace llvm; 45 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. 49static cl::opt<bool> 50EnableScopedNoAlias("enable-scoped-noalias", cl::init(true)); 51 52namespace { 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. 56class AliasScopeNode { 57 const MDNode *Node; 58 59public: 60 AliasScopeNode() : Node(0) {} 61 explicit AliasScopeNode(const MDNode *N) : Node(N) {} 62 63 /// getNode - Get the MDNode for this AliasScopeNode. 64 const MDNode *getNode() const { return Node; } 65 66 /// getDomain - Get the MDNode for this AliasScopeNode's domain. 67 const MDNode *getDomain() const { 68 if (Node->getNumOperands() < 2) 69 return nullptr; 70 return dyn_cast_or_null<MDNode>(Node->getOperand(1)); 71 } 72}; 73 74/// ScopedNoAliasAA - This is a simple alias analysis 75/// implementation that uses scoped-noalias metadata to answer queries. 76class ScopedNoAliasAA : public ImmutablePass, public AliasAnalysis { 77public: 78 static char ID; // Class identification, replacement for typeinfo 79 ScopedNoAliasAA() : ImmutablePass(ID) { 80 initializeScopedNoAliasAAPass(*PassRegistry::getPassRegistry()); 81 } 82 83 bool doInitialization(Module &M) override; 84 85 /// getAdjustedAnalysisPointer - This method is used when a pass implements 86 /// an analysis interface through multiple inheritance. If needed, it 87 /// should override this to adjust the this pointer as needed for the 88 /// specified pass info. 89 void *getAdjustedAnalysisPointer(const void *PI) override { 90 if (PI == &AliasAnalysis::ID) 91 return (AliasAnalysis*)this; 92 return this; 93 } 94 95protected: 96 bool mayAliasInScopes(const MDNode *Scopes, const MDNode *NoAlias) const; 97 void collectMDInDomain(const MDNode *List, const MDNode *Domain, 98 SmallPtrSetImpl<const MDNode *> &Nodes) const; 99 100private: 101 void getAnalysisUsage(AnalysisUsage &AU) const override; 102 AliasResult alias(const MemoryLocation &LocA, 103 const MemoryLocation &LocB) override; 104 bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal) override; 105 ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override; 106 ModRefBehavior getModRefBehavior(const Function *F) override; 107 ModRefResult getModRefInfo(ImmutableCallSite CS, 108 const MemoryLocation &Loc) override; 109 ModRefResult getModRefInfo(ImmutableCallSite CS1, 110 ImmutableCallSite CS2) override; 111}; 112} // End of anonymous namespace 113 114// Register this pass... 115char ScopedNoAliasAA::ID = 0; 116INITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias", 117 "Scoped NoAlias Alias Analysis", false, true, false) 118 119ImmutablePass *llvm::createScopedNoAliasAAPass() { 120 return new ScopedNoAliasAA(); 121} 122 123bool ScopedNoAliasAA::doInitialization(Module &M) { 124 InitializeAliasAnalysis(this, &M.getDataLayout()); 125 return true; 126} 127 128void 129ScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const { 130 AU.setPreservesAll(); 131 AliasAnalysis::getAnalysisUsage(AU); 132} 133 134void 135ScopedNoAliasAA::collectMDInDomain(const MDNode *List, const MDNode *Domain, 136 SmallPtrSetImpl<const MDNode *> &Nodes) const { 137 for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i) 138 if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i))) 139 if (AliasScopeNode(MD).getDomain() == Domain) 140 Nodes.insert(MD); 141} 142 143bool 144ScopedNoAliasAA::mayAliasInScopes(const MDNode *Scopes, 145 const MDNode *NoAlias) const { 146 if (!Scopes || !NoAlias) 147 return true; 148 149 // Collect the set of scope domains relevant to the noalias scopes. 150 SmallPtrSet<const MDNode *, 16> Domains; 151 for (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i) 152 if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i))) 153 if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain()) 154 Domains.insert(Domain); 155 156 // We alias unless, for some domain, the set of noalias scopes in that domain 157 // is a superset of the set of alias scopes in that domain. 158 for (const MDNode *Domain : Domains) { 159 SmallPtrSet<const MDNode *, 16> NANodes, ScopeNodes; 160 collectMDInDomain(NoAlias, Domain, NANodes); 161 collectMDInDomain(Scopes, Domain, ScopeNodes); 162 if (!ScopeNodes.size()) 163 continue; 164 165 // To not alias, all of the nodes in ScopeNodes must be in NANodes. 166 bool FoundAll = true; 167 for (const MDNode *SMD : ScopeNodes) 168 if (!NANodes.count(SMD)) { 169 FoundAll = false; 170 break; 171 } 172 173 if (FoundAll) 174 return false; 175 } 176 177 return true; 178} 179 180AliasResult ScopedNoAliasAA::alias(const MemoryLocation &LocA, 181 const MemoryLocation &LocB) { 182 if (!EnableScopedNoAlias) 183 return AliasAnalysis::alias(LocA, LocB); 184 185 // Get the attached MDNodes. 186 const MDNode *AScopes = LocA.AATags.Scope, 187 *BScopes = LocB.AATags.Scope; 188 189 const MDNode *ANoAlias = LocA.AATags.NoAlias, 190 *BNoAlias = LocB.AATags.NoAlias; 191 192 if (!mayAliasInScopes(AScopes, BNoAlias)) 193 return NoAlias; 194 195 if (!mayAliasInScopes(BScopes, ANoAlias)) 196 return NoAlias; 197 198 // If they may alias, chain to the next AliasAnalysis. 199 return AliasAnalysis::alias(LocA, LocB); 200} 201 202bool ScopedNoAliasAA::pointsToConstantMemory(const MemoryLocation &Loc, 203 bool OrLocal) { 204 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 205} 206 207AliasAnalysis::ModRefBehavior 208ScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) { 209 return AliasAnalysis::getModRefBehavior(CS); 210} 211 212AliasAnalysis::ModRefBehavior 213ScopedNoAliasAA::getModRefBehavior(const Function *F) { 214 return AliasAnalysis::getModRefBehavior(F); 215} 216 217AliasAnalysis::ModRefResult 218ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS, 219 const MemoryLocation &Loc) { 220 if (!EnableScopedNoAlias) 221 return AliasAnalysis::getModRefInfo(CS, Loc); 222 223 if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata( 224 LLVMContext::MD_noalias))) 225 return NoModRef; 226 227 if (!mayAliasInScopes( 228 CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 229 Loc.AATags.NoAlias)) 230 return NoModRef; 231 232 return AliasAnalysis::getModRefInfo(CS, Loc); 233} 234 235AliasAnalysis::ModRefResult 236ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) { 237 if (!EnableScopedNoAlias) 238 return AliasAnalysis::getModRefInfo(CS1, CS2); 239 240 if (!mayAliasInScopes( 241 CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 242 CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias))) 243 return NoModRef; 244 245 if (!mayAliasInScopes( 246 CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 247 CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias))) 248 return NoModRef; 249 250 return AliasAnalysis::getModRefInfo(CS1, CS2); 251} 252 253