ScopedNoAliasAA.cpp revision 280031
117651Speter//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===// 2131377Stjr// 317651Speter// The LLVM Compiler Infrastructure 4206708Sdelphij// 5206708Sdelphij// This file is distributed under the University of Illinois Open Source 6206708Sdelphij// License. See LICENSE.TXT for details. 7206708Sdelphij// 8206708Sdelphij//===----------------------------------------------------------------------===// 9206708Sdelphij// 10206708Sdelphij// This file defines the ScopedNoAlias alias-analysis pass, which implements 11206708Sdelphij// metadata-based scoped no-alias support. 12206708Sdelphij// 13206708Sdelphij// Alias-analysis scopes are defined by an id (which can be a string or some 14206708Sdelphij// other metadata node), a domain node, and an optional descriptive string. 15206708Sdelphij// A domain is defined by an id (which can be a string or some other metadata 16206708Sdelphij// node), and an optional descriptive string. 17206708Sdelphij// 18206708Sdelphij// !dom0 = metadata !{ metadata !"domain of foo()" } 19206708Sdelphij// !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" } 20206708Sdelphij// !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" } 21206708Sdelphij// 22206708Sdelphij// Loads and stores can be tagged with an alias-analysis scope, and also, with 23206708Sdelphij// a noalias tag for a specific scope: 24206708Sdelphij// 25206708Sdelphij// ... = load %ptr1, !alias.scope !{ !scope1 } 26206708Sdelphij// ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 } 27206708Sdelphij// 28206708Sdelphij// When evaluating an aliasing query, if one of the instructions is associated 29206708Sdelphij// has a set of noalias scopes in some domain that is superset of the alias 30206708Sdelphij// scopes in that domain of some other instruction, then the two memory 31206708Sdelphij// accesses are assumed not to alias. 32206002Sdelphij// 33206002Sdelphij//===----------------------------------------------------------------------===// 34206002Sdelphij 35206002Sdelphij#include "llvm/ADT/SmallPtrSet.h" 36206002Sdelphij#include "llvm/Analysis/AliasAnalysis.h" 37206002Sdelphij#include "llvm/Analysis/Passes.h" 38206002Sdelphij#include "llvm/IR/Constants.h" 39206002Sdelphij#include "llvm/IR/LLVMContext.h" 40206002Sdelphij#include "llvm/IR/Metadata.h" 41206002Sdelphij#include "llvm/IR/Module.h" 42206002Sdelphij#include "llvm/Pass.h" 43206002Sdelphij#include "llvm/Support/CommandLine.h" 44206002Sdelphijusing namespace llvm; 45206002Sdelphij 46206002Sdelphij// A handy option for disabling scoped no-alias functionality. The same effect 47206002Sdelphij// can also be achieved by stripping the associated metadata tags from IR, but 48206002Sdelphij// this option is sometimes more convenient. 49206002Sdelphijstatic cl::opt<bool> 50206002SdelphijEnableScopedNoAlias("enable-scoped-noalias", cl::init(true)); 51206002Sdelphij 52206002Sdelphijnamespace { 53206002Sdelphij/// AliasScopeNode - This is a simple wrapper around an MDNode which provides 54206002Sdelphij/// a higher-level interface by hiding the details of how alias analysis 55206002Sdelphij/// information is encoded in its operands. 56205471Sdelphijclass AliasScopeNode { 57205471Sdelphij const MDNode *Node; 58205471Sdelphij 59205471Sdelphijpublic: 60205471Sdelphij AliasScopeNode() : Node(0) {} 61205471Sdelphij explicit AliasScopeNode(const MDNode *N) : Node(N) {} 62205471Sdelphij 63205471Sdelphij /// getNode - Get the MDNode for this AliasScopeNode. 64205471Sdelphij const MDNode *getNode() const { return Node; } 65205471Sdelphij 66205471Sdelphij /// getDomain - Get the MDNode for this AliasScopeNode's domain. 67205471Sdelphij const MDNode *getDomain() const { 68205471Sdelphij if (Node->getNumOperands() < 2) 69205471Sdelphij return nullptr; 70205471Sdelphij return dyn_cast_or_null<MDNode>(Node->getOperand(1)); 71205471Sdelphij } 72205471Sdelphij}; 73205471Sdelphij 74205471Sdelphij/// ScopedNoAliasAA - This is a simple alias analysis 75205471Sdelphij/// implementation that uses scoped-noalias metadata to answer queries. 76205471Sdelphijclass ScopedNoAliasAA : public ImmutablePass, public AliasAnalysis { 77205471Sdelphijpublic: 78205471Sdelphij static char ID; // Class identification, replacement for typeinfo 79205471Sdelphij ScopedNoAliasAA() : ImmutablePass(ID) { 80205471Sdelphij initializeScopedNoAliasAAPass(*PassRegistry::getPassRegistry()); 81205471Sdelphij } 82205471Sdelphij 83205471Sdelphij void initializePass() override { InitializeAliasAnalysis(this); } 84205471Sdelphij 85205471Sdelphij /// getAdjustedAnalysisPointer - This method is used when a pass implements 86205471Sdelphij /// an analysis interface through multiple inheritance. If needed, it 87205471Sdelphij /// should override this to adjust the this pointer as needed for the 88205471Sdelphij /// specified pass info. 89205471Sdelphij void *getAdjustedAnalysisPointer(const void *PI) override { 90205471Sdelphij if (PI == &AliasAnalysis::ID) 91205471Sdelphij return (AliasAnalysis*)this; 92205471Sdelphij return this; 93205471Sdelphij } 94205471Sdelphij 95205471Sdelphijprotected: 96205471Sdelphij bool mayAliasInScopes(const MDNode *Scopes, const MDNode *NoAlias) const; 97205471Sdelphij void collectMDInDomain(const MDNode *List, const MDNode *Domain, 98205471Sdelphij SmallPtrSetImpl<const MDNode *> &Nodes) const; 99205471Sdelphij 100205471Sdelphijprivate: 101205471Sdelphij void getAnalysisUsage(AnalysisUsage &AU) const override; 102205471Sdelphij AliasResult alias(const Location &LocA, const Location &LocB) override; 103205471Sdelphij bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override; 104205471Sdelphij ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override; 105205471Sdelphij ModRefBehavior getModRefBehavior(const Function *F) override; 106205471Sdelphij ModRefResult getModRefInfo(ImmutableCallSite CS, 107205471Sdelphij const Location &Loc) override; 108205471Sdelphij ModRefResult getModRefInfo(ImmutableCallSite CS1, 109205471Sdelphij ImmutableCallSite CS2) override; 110205471Sdelphij}; 111205471Sdelphij} // End of anonymous namespace 112205471Sdelphij 113205471Sdelphij// Register this pass... 114205471Sdelphijchar ScopedNoAliasAA::ID = 0; 115205471SdelphijINITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias", 116205471Sdelphij "Scoped NoAlias Alias Analysis", false, true, false) 117205471Sdelphij 118205471SdelphijImmutablePass *llvm::createScopedNoAliasAAPass() { 119205471Sdelphij return new ScopedNoAliasAA(); 120205471Sdelphij} 121205471Sdelphij 122205471Sdelphijvoid 123205471SdelphijScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const { 124205471Sdelphij AU.setPreservesAll(); 125205471Sdelphij AliasAnalysis::getAnalysisUsage(AU); 126205471Sdelphij} 127205471Sdelphij 128205471Sdelphijvoid 129205471SdelphijScopedNoAliasAA::collectMDInDomain(const MDNode *List, const MDNode *Domain, 130205471Sdelphij SmallPtrSetImpl<const MDNode *> &Nodes) const { 131205471Sdelphij for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i) 132205471Sdelphij if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i))) 133205471Sdelphij if (AliasScopeNode(MD).getDomain() == Domain) 134205471Sdelphij Nodes.insert(MD); 135205471Sdelphij} 136205471Sdelphij 137205471Sdelphijbool 138205471SdelphijScopedNoAliasAA::mayAliasInScopes(const MDNode *Scopes, 139205471Sdelphij const MDNode *NoAlias) const { 140205471Sdelphij if (!Scopes || !NoAlias) 141205471Sdelphij return true; 142205471Sdelphij 143205471Sdelphij // Collect the set of scope domains relevant to the noalias scopes. 144205471Sdelphij SmallPtrSet<const MDNode *, 16> Domains; 145205471Sdelphij for (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i) 146205471Sdelphij if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i))) 147205471Sdelphij if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain()) 148205471Sdelphij Domains.insert(Domain); 149205471Sdelphij 150205471Sdelphij // We alias unless, for some domain, the set of noalias scopes in that domain 151205471Sdelphij // is a superset of the set of alias scopes in that domain. 152205471Sdelphij for (const MDNode *Domain : Domains) { 153205471Sdelphij SmallPtrSet<const MDNode *, 16> NANodes, ScopeNodes; 154205471Sdelphij collectMDInDomain(NoAlias, Domain, NANodes); 155205471Sdelphij collectMDInDomain(Scopes, Domain, ScopeNodes); 156205471Sdelphij if (!ScopeNodes.size()) 157205471Sdelphij continue; 158205471Sdelphij 159205471Sdelphij // To not alias, all of the nodes in ScopeNodes must be in NANodes. 160205471Sdelphij bool FoundAll = true; 161205471Sdelphij for (const MDNode *SMD : ScopeNodes) 162205471Sdelphij if (!NANodes.count(SMD)) { 163205471Sdelphij FoundAll = false; 164205471Sdelphij break; 165205471Sdelphij } 166205471Sdelphij 167205471Sdelphij if (FoundAll) 168205471Sdelphij return false; 169205471Sdelphij } 170205471Sdelphij 171205471Sdelphij return true; 172205471Sdelphij} 173205471Sdelphij 174205471SdelphijAliasAnalysis::AliasResult 175205471SdelphijScopedNoAliasAA::alias(const Location &LocA, const Location &LocB) { 176205471Sdelphij if (!EnableScopedNoAlias) 177205471Sdelphij return AliasAnalysis::alias(LocA, LocB); 178205471Sdelphij 179205471Sdelphij // Get the attached MDNodes. 180205471Sdelphij const MDNode *AScopes = LocA.AATags.Scope, 181205471Sdelphij *BScopes = LocB.AATags.Scope; 182205471Sdelphij 183205471Sdelphij const MDNode *ANoAlias = LocA.AATags.NoAlias, 184205471Sdelphij *BNoAlias = LocB.AATags.NoAlias; 185205471Sdelphij 186205471Sdelphij if (!mayAliasInScopes(AScopes, BNoAlias)) 187205471Sdelphij return NoAlias; 188205471Sdelphij 189205471Sdelphij if (!mayAliasInScopes(BScopes, ANoAlias)) 190205471Sdelphij return NoAlias; 191205471Sdelphij 192205471Sdelphij // If they may alias, chain to the next AliasAnalysis. 193205471Sdelphij return AliasAnalysis::alias(LocA, LocB); 194205471Sdelphij} 195205471Sdelphij 196205471Sdelphijbool ScopedNoAliasAA::pointsToConstantMemory(const Location &Loc, 197205471Sdelphij bool OrLocal) { 198205471Sdelphij return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 199205471Sdelphij} 200205471Sdelphij 201205471SdelphijAliasAnalysis::ModRefBehavior 202205471SdelphijScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) { 203205471Sdelphij return AliasAnalysis::getModRefBehavior(CS); 204205471Sdelphij} 205205471Sdelphij 206205471SdelphijAliasAnalysis::ModRefBehavior 207205471SdelphijScopedNoAliasAA::getModRefBehavior(const Function *F) { 208205471Sdelphij return AliasAnalysis::getModRefBehavior(F); 209205471Sdelphij} 210205471Sdelphij 211205471SdelphijAliasAnalysis::ModRefResult 212205471SdelphijScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { 213205471Sdelphij if (!EnableScopedNoAlias) 214205471Sdelphij return AliasAnalysis::getModRefInfo(CS, Loc); 215205471Sdelphij 216205471Sdelphij if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata( 217205471Sdelphij LLVMContext::MD_noalias))) 218205471Sdelphij return NoModRef; 219205471Sdelphij 220205471Sdelphij if (!mayAliasInScopes( 221205471Sdelphij CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 222205471Sdelphij Loc.AATags.NoAlias)) 223205471Sdelphij return NoModRef; 224205471Sdelphij 225205471Sdelphij return AliasAnalysis::getModRefInfo(CS, Loc); 226205471Sdelphij} 227205471Sdelphij 228205471SdelphijAliasAnalysis::ModRefResult 229205471SdelphijScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) { 230205471Sdelphij if (!EnableScopedNoAlias) 231205471Sdelphij return AliasAnalysis::getModRefInfo(CS1, CS2); 232205471Sdelphij 233205471Sdelphij if (!mayAliasInScopes( 234205471Sdelphij CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 235205471Sdelphij CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias))) 236205471Sdelphij return NoModRef; 237205471Sdelphij 238205471Sdelphij if (!mayAliasInScopes( 239205471Sdelphij CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope), 240205471Sdelphij CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias))) 241205471Sdelphij return NoModRef; 242205471Sdelphij 243205471Sdelphij return AliasAnalysis::getModRefInfo(CS1, CS2); 244205471Sdelphij} 245205471Sdelphij 246205471Sdelphij