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1e3557de0d
This will allow classes to implement the AA interface without deriving from the class or referencing an internal enum of some other class as their return types. Also, to a pretty fundamental extent, concepts such as 'NoAlias', 'MayAlias', and 'MustAlias' are first class concepts in LLVM and we aren't saving anything by scoping them heavily. My mild preference would have been to use a scoped enum, but that feature is essentially completely broken AFAICT. I'm extremely disappointed. For example, we cannot through any reasonable[1] means construct an enum class (or analog) which has scoped names but converts to a boolean in order to test for the possibility of aliasing. [1]: Richard Smith came up with a "solution", but it requires class templates, and lots of boilerplate setting up the enumeration multiple times. Something like Boost.PP could potentially bundle this up, but even that would be quite painful and it doesn't seem realistically worth it. The enum class solution would probably work without the need for a bool conversion. Differential Revision: http://reviews.llvm.org/D10495 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240255 91177308-0d34-0410-b5e6-96231b3b80d8
253 lines
8.8 KiB
C++
253 lines
8.8 KiB
C++
//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the ScopedNoAlias alias-analysis pass, which implements
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// metadata-based scoped no-alias support.
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//
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// Alias-analysis scopes are defined by an id (which can be a string or some
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// other metadata node), a domain node, and an optional descriptive string.
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// A domain is defined by an id (which can be a string or some other metadata
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// node), and an optional descriptive string.
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//
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// !dom0 = metadata !{ metadata !"domain of foo()" }
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// !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" }
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// !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" }
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//
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// Loads and stores can be tagged with an alias-analysis scope, and also, with
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// a noalias tag for a specific scope:
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//
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// ... = load %ptr1, !alias.scope !{ !scope1 }
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// ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 }
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//
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// When evaluating an aliasing query, if one of the instructions is associated
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// has a set of noalias scopes in some domain that is superset of the alias
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// scopes in that domain of some other instruction, then the two memory
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// accesses are assumed not to alias.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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using namespace llvm;
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// A handy option for disabling scoped no-alias functionality. The same effect
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// can also be achieved by stripping the associated metadata tags from IR, but
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// this option is sometimes more convenient.
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static cl::opt<bool>
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EnableScopedNoAlias("enable-scoped-noalias", cl::init(true));
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namespace {
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/// AliasScopeNode - This is a simple wrapper around an MDNode which provides
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/// a higher-level interface by hiding the details of how alias analysis
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/// information is encoded in its operands.
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class AliasScopeNode {
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const MDNode *Node;
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public:
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AliasScopeNode() : Node(0) {}
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explicit AliasScopeNode(const MDNode *N) : Node(N) {}
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/// getNode - Get the MDNode for this AliasScopeNode.
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const MDNode *getNode() const { return Node; }
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/// getDomain - Get the MDNode for this AliasScopeNode's domain.
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const MDNode *getDomain() const {
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if (Node->getNumOperands() < 2)
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return nullptr;
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return dyn_cast_or_null<MDNode>(Node->getOperand(1));
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}
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};
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/// ScopedNoAliasAA - This is a simple alias analysis
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/// implementation that uses scoped-noalias metadata to answer queries.
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class ScopedNoAliasAA : public ImmutablePass, public AliasAnalysis {
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public:
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static char ID; // Class identification, replacement for typeinfo
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ScopedNoAliasAA() : ImmutablePass(ID) {
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initializeScopedNoAliasAAPass(*PassRegistry::getPassRegistry());
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}
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bool doInitialization(Module &M) override;
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/// getAdjustedAnalysisPointer - This method is used when a pass implements
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/// an analysis interface through multiple inheritance. If needed, it
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/// should override this to adjust the this pointer as needed for the
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/// specified pass info.
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void *getAdjustedAnalysisPointer(const void *PI) override {
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if (PI == &AliasAnalysis::ID)
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return (AliasAnalysis*)this;
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return this;
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}
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protected:
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bool mayAliasInScopes(const MDNode *Scopes, const MDNode *NoAlias) const;
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void collectMDInDomain(const MDNode *List, const MDNode *Domain,
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SmallPtrSetImpl<const MDNode *> &Nodes) const;
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private:
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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AliasResult alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) override;
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bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal) override;
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ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
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ModRefBehavior getModRefBehavior(const Function *F) override;
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ModRefResult getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) override;
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ModRefResult getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) override;
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};
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} // End of anonymous namespace
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// Register this pass...
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char ScopedNoAliasAA::ID = 0;
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INITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias",
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"Scoped NoAlias Alias Analysis", false, true, false)
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ImmutablePass *llvm::createScopedNoAliasAAPass() {
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return new ScopedNoAliasAA();
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}
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bool ScopedNoAliasAA::doInitialization(Module &M) {
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InitializeAliasAnalysis(this, &M.getDataLayout());
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return true;
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}
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void
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ScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AliasAnalysis::getAnalysisUsage(AU);
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}
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void
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ScopedNoAliasAA::collectMDInDomain(const MDNode *List, const MDNode *Domain,
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SmallPtrSetImpl<const MDNode *> &Nodes) const {
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for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i)
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if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i)))
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if (AliasScopeNode(MD).getDomain() == Domain)
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Nodes.insert(MD);
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}
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bool
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ScopedNoAliasAA::mayAliasInScopes(const MDNode *Scopes,
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const MDNode *NoAlias) const {
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if (!Scopes || !NoAlias)
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return true;
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// Collect the set of scope domains relevant to the noalias scopes.
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SmallPtrSet<const MDNode *, 16> Domains;
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for (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i)
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if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i)))
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if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())
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Domains.insert(Domain);
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// We alias unless, for some domain, the set of noalias scopes in that domain
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// is a superset of the set of alias scopes in that domain.
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for (const MDNode *Domain : Domains) {
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SmallPtrSet<const MDNode *, 16> NANodes, ScopeNodes;
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collectMDInDomain(NoAlias, Domain, NANodes);
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collectMDInDomain(Scopes, Domain, ScopeNodes);
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if (!ScopeNodes.size())
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continue;
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// To not alias, all of the nodes in ScopeNodes must be in NANodes.
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bool FoundAll = true;
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for (const MDNode *SMD : ScopeNodes)
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if (!NANodes.count(SMD)) {
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FoundAll = false;
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break;
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}
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if (FoundAll)
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return false;
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}
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return true;
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}
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AliasResult ScopedNoAliasAA::alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::alias(LocA, LocB);
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// Get the attached MDNodes.
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const MDNode *AScopes = LocA.AATags.Scope,
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*BScopes = LocB.AATags.Scope;
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const MDNode *ANoAlias = LocA.AATags.NoAlias,
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*BNoAlias = LocB.AATags.NoAlias;
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if (!mayAliasInScopes(AScopes, BNoAlias))
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return NoAlias;
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if (!mayAliasInScopes(BScopes, ANoAlias))
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return NoAlias;
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// If they may alias, chain to the next AliasAnalysis.
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return AliasAnalysis::alias(LocA, LocB);
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}
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bool ScopedNoAliasAA::pointsToConstantMemory(const MemoryLocation &Loc,
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bool OrLocal) {
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return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
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}
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AliasAnalysis::ModRefBehavior
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ScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) {
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return AliasAnalysis::getModRefBehavior(CS);
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}
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AliasAnalysis::ModRefBehavior
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ScopedNoAliasAA::getModRefBehavior(const Function *F) {
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return AliasAnalysis::getModRefBehavior(F);
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}
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AliasAnalysis::ModRefResult
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ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::getModRefInfo(CS, Loc);
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if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata(
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LLVMContext::MD_noalias)))
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return NoModRef;
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if (!mayAliasInScopes(
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CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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Loc.AATags.NoAlias))
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return NoModRef;
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return AliasAnalysis::getModRefInfo(CS, Loc);
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}
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AliasAnalysis::ModRefResult
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ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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if (!mayAliasInScopes(
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CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
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return NoModRef;
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if (!mayAliasInScopes(
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CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
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return NoModRef;
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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}
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