//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file defines the ScopedNoAlias alias-analysis pass, which implements

// metadata-based scoped no-alias support.

//

// Alias-analysis scopes are defined by an id (which can be a string or some

// other metadata node), a domain node, and an optional descriptive string.

// A domain is defined by an id (which can be a string or some other metadata

// node), and an optional descriptive string.

//

// !dom0 =   metadata !{ metadata !"domain of foo()" }

// !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" }

// !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" }

//

// Loads and stores can be tagged with an alias-analysis scope, and also, with

// a noalias tag for a specific scope:

//

// ... = load %ptr1, !alias.scope !{ !scope1 }

// ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 }

//

// When evaluating an aliasing query, if one of the instructions is associated

// has a set of noalias scopes in some domain that is a superset of the alias

// scopes in that domain of some other instruction, then the two memory

// accesses are assumed not to alias.

//

//===----------------------------------------------------------------------===//

#include "llvm/Analysis/ScopedNoAliasAA.h"

#include "llvm/ADT/SetOperations.h"

#include "llvm/ADT/SmallPtrSet.h"

#include "llvm/Analysis/MemoryLocation.h"

#include "llvm/IR/InstrTypes.h"

#include "llvm/IR/LLVMContext.h"

#include "llvm/IR/Metadata.h"

#include "llvm/InitializePasses.h"

#include "llvm/Pass.h"

#include "llvm/Support/Casting.h"

#include "llvm/Support/CommandLine.h"

using namespace llvm;

// A handy option for disabling scoped no-alias functionality. The same effect

// can also be achieved by stripping the associated metadata tags from IR, but

// this option is sometimes more convenient.

static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias",

                                         cl::init(true), cl::Hidden);

AliasResult ScopedNoAliasAAResult::alias(const MemoryLocation &LocA,

                                         const MemoryLocation &LocB,

                                         AAQueryInfo &AAQI,

                                         const Instruction *) {

  if (!EnableScopedNoAlias)

    return AliasResult::MayAlias;

  // Get the attached MDNodes.

  const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope;

  const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias;

  if (!mayAliasInScopes(AScopes, BNoAlias))

    return AliasResult::NoAlias;

  if (!mayAliasInScopes(BScopes, ANoAlias))

    return AliasResult::NoAlias;

  return AliasResult::MayAlias;

}

ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call,

                                                const MemoryLocation &Loc,

                                                AAQueryInfo &AAQI) {

  if (!EnableScopedNoAlias)

    return ModRefInfo::ModRef;

  if (!mayAliasInScopes(Loc.AATags.Scope,

                        Call->getMetadata(LLVMContext::MD_noalias)))

    return ModRefInfo::NoModRef;

  if (!mayAliasInScopes(Call->getMetadata(LLVMContext::MD_alias_scope),

                        Loc.AATags.NoAlias))

    return ModRefInfo::NoModRef;

  return ModRefInfo::ModRef;

}

ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call1,

                                                const CallBase *Call2,

                                                AAQueryInfo &AAQI) {

  if (!EnableScopedNoAlias)

    return ModRefInfo::ModRef;

  if (!mayAliasInScopes(Call1->getMetadata(LLVMContext::MD_alias_scope),

                        Call2->getMetadata(LLVMContext::MD_noalias)))

    return ModRefInfo::NoModRef;

  if (!mayAliasInScopes(Call2->getMetadata(LLVMContext::MD_alias_scope),

                        Call1->getMetadata(LLVMContext::MD_noalias)))

    return ModRefInfo::NoModRef;

  return ModRefInfo::ModRef;

}

static void collectMDInDomain(const MDNode *List, const MDNode *Domain,

                              SmallPtrSetImpl<const MDNode *> &Nodes) {

  for (const MDOperand &MDOp : List->operands())

    if (const MDNode *MD = dyn_cast<MDNode>(MDOp))

      if (AliasScopeNode(MD).getDomain() == Domain)

        Nodes.insert(MD);

}

bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes,

                                             const MDNode *NoAlias) const {

  if (!Scopes || !NoAlias)

    return true;

  // Collect the set of scope domains relevant to the noalias scopes.

  SmallPtrSet<const MDNode *, 16> Domains;

  for (const MDOperand &MDOp : NoAlias->operands())

    if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp))

      if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())

        Domains.insert(Domain);

  // We alias unless, for some domain, the set of noalias scopes in that domain

  // is a superset of the set of alias scopes in that domain.

  for (const MDNode *Domain : Domains) {

    SmallPtrSet<const MDNode *, 16> ScopeNodes;

    collectMDInDomain(Scopes, Domain, ScopeNodes);

    if (ScopeNodes.empty())

      continue;

    SmallPtrSet<const MDNode *, 16> NANodes;

    collectMDInDomain(NoAlias, Domain, NANodes);

    // To not alias, all of the nodes in ScopeNodes must be in NANodes.

    if (llvm::set_is_subset(ScopeNodes, NANodes))

      return false;

  }

  return true;

}

AnalysisKey ScopedNoAliasAA::Key;

ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F,

                                           FunctionAnalysisManager &AM) {

  return ScopedNoAliasAAResult();

}

char ScopedNoAliasAAWrapperPass::ID = 0;

INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias-aa",

                "Scoped NoAlias Alias Analysis", false, true)

ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() {

  return new ScopedNoAliasAAWrapperPass();

}

ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) {

  initializeScopedNoAliasAAWrapperPassPass(*PassRegistry::getPassRegistry());

}

bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) {

  Result.reset(new ScopedNoAliasAAResult());

  return false;

}

bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) {

  Result.reset();

  return false;

}

void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {

  AU.setPreservesAll();

}