LLVM  15.0.0git
ScopedNoAliasAA.cpp
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1 //===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the ScopedNoAlias alias-analysis pass, which implements
10 // metadata-based scoped no-alias support.
11 //
12 // Alias-analysis scopes are defined by an id (which can be a string or some
13 // other metadata node), a domain node, and an optional descriptive string.
14 // A domain is defined by an id (which can be a string or some other metadata
15 // node), and an optional descriptive string.
16 //
17 // !dom0 = metadata !{ metadata !"domain of foo()" }
18 // !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" }
19 // !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" }
20 //
21 // Loads and stores can be tagged with an alias-analysis scope, and also, with
22 // a noalias tag for a specific scope:
23 //
24 // ... = load %ptr1, !alias.scope !{ !scope1 }
25 // ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 }
26 //
27 // When evaluating an aliasing query, if one of the instructions is associated
28 // has a set of noalias scopes in some domain that is a superset of the alias
29 // scopes in that domain of some other instruction, then the two memory
30 // accesses are assumed not to alias.
31 //
32 //===----------------------------------------------------------------------===//
33 
35 #include "llvm/ADT/SetOperations.h"
36 #include "llvm/ADT/SmallPtrSet.h"
38 #include "llvm/IR/InstrTypes.h"
39 #include "llvm/IR/LLVMContext.h"
40 #include "llvm/IR/Metadata.h"
41 #include "llvm/InitializePasses.h"
42 #include "llvm/Pass.h"
43 #include "llvm/Support/Casting.h"
45 
46 using namespace llvm;
47 
48 // A handy option for disabling scoped no-alias functionality. The same effect
49 // can also be achieved by stripping the associated metadata tags from IR, but
50 // this option is sometimes more convenient.
51 static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias",
52  cl::init(true), cl::Hidden);
53 
55  const MemoryLocation &LocB,
56  AAQueryInfo &AAQI) {
58  return AAResultBase::alias(LocA, LocB, AAQI);
59 
60  // Get the attached MDNodes.
61  const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope;
62 
63  const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias;
64 
65  if (!mayAliasInScopes(AScopes, BNoAlias))
66  return AliasResult::NoAlias;
67 
68  if (!mayAliasInScopes(BScopes, ANoAlias))
69  return AliasResult::NoAlias;
70 
71  // If they may alias, chain to the next AliasAnalysis.
72  return AAResultBase::alias(LocA, LocB, AAQI);
73 }
74 
76  const MemoryLocation &Loc,
77  AAQueryInfo &AAQI) {
79  return AAResultBase::getModRefInfo(Call, Loc, AAQI);
80 
81  if (!mayAliasInScopes(Loc.AATags.Scope,
82  Call->getMetadata(LLVMContext::MD_noalias)))
83  return ModRefInfo::NoModRef;
84 
85  if (!mayAliasInScopes(Call->getMetadata(LLVMContext::MD_alias_scope),
86  Loc.AATags.NoAlias))
87  return ModRefInfo::NoModRef;
88 
89  return AAResultBase::getModRefInfo(Call, Loc, AAQI);
90 }
91 
93  const CallBase *Call2,
94  AAQueryInfo &AAQI) {
96  return AAResultBase::getModRefInfo(Call1, Call2, AAQI);
97 
98  if (!mayAliasInScopes(Call1->getMetadata(LLVMContext::MD_alias_scope),
99  Call2->getMetadata(LLVMContext::MD_noalias)))
100  return ModRefInfo::NoModRef;
101 
102  if (!mayAliasInScopes(Call2->getMetadata(LLVMContext::MD_alias_scope),
103  Call1->getMetadata(LLVMContext::MD_noalias)))
104  return ModRefInfo::NoModRef;
105 
106  return AAResultBase::getModRefInfo(Call1, Call2, AAQI);
107 }
108 
109 static void collectMDInDomain(const MDNode *List, const MDNode *Domain,
111  for (const MDOperand &MDOp : List->operands())
112  if (const MDNode *MD = dyn_cast<MDNode>(MDOp))
113  if (AliasScopeNode(MD).getDomain() == Domain)
114  Nodes.insert(MD);
115 }
116 
117 bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes,
118  const MDNode *NoAlias) const {
119  if (!Scopes || !NoAlias)
120  return true;
121 
122  // Collect the set of scope domains relevant to the noalias scopes.
124  for (const MDOperand &MDOp : NoAlias->operands())
125  if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp))
126  if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())
127  Domains.insert(Domain);
128 
129  // We alias unless, for some domain, the set of noalias scopes in that domain
130  // is a superset of the set of alias scopes in that domain.
131  for (const MDNode *Domain : Domains) {
133  collectMDInDomain(Scopes, Domain, ScopeNodes);
134  if (ScopeNodes.empty())
135  continue;
136 
138  collectMDInDomain(NoAlias, Domain, NANodes);
139 
140  // To not alias, all of the nodes in ScopeNodes must be in NANodes.
141  if (llvm::set_is_subset(ScopeNodes, NANodes))
142  return false;
143  }
144 
145  return true;
146 }
147 
148 AnalysisKey ScopedNoAliasAA::Key;
149 
152  return ScopedNoAliasAAResult();
153 }
154 
156 
158  "Scoped NoAlias Alias Analysis", false, true)
159 
161  return new ScopedNoAliasAAWrapperPass();
162 }
163 
166 }
167 
169  Result.reset(new ScopedNoAliasAAResult());
170  return false;
171 }
172 
174  Result.reset();
175  return false;
176 }
177 
179  AU.setPreservesAll();
180 }
llvm::ModRefInfo::NoModRef
@ NoModRef
The access neither references nor modifies the value stored in memory.
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
llvm::initializeScopedNoAliasAAWrapperPassPass
void initializeScopedNoAliasAAWrapperPassPass(PassRegistry &)
llvm::set_is_subset
bool set_is_subset(const S1Ty &S1, const S2Ty &S2)
set_is_subset(A, B) - Return true iff A in B
Definition: SetOperations.h:72
llvm::ScopedNoAliasAAWrapperPass::doInitialization
bool doInitialization(Module &M) override
doInitialization - Virtual method overridden by subclasses to do any necessary initialization before ...
Definition: ScopedNoAliasAA.cpp:168
Metadata.h
llvm::ImmutablePass
ImmutablePass class - This class is used to provide information that does not need to be run.
Definition: Pass.h:279
SetOperations.h
llvm::Function
Definition: Function.h:60
Pass.h
EnableScopedNoAlias
static cl::opt< bool > EnableScopedNoAlias("enable-scoped-noalias", cl::init(true), cl::Hidden)
llvm::cl::Hidden
@ Hidden
Definition: CommandLine.h:139
llvm::AliasResult
The possible results of an alias query.
Definition: AliasAnalysis.h:81
llvm::SmallPtrSet
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:450
llvm::AAMDNodes::Scope
MDNode * Scope
The tag for alias scope specification (used with noalias).
Definition: Metadata.h:675
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::AAQueryInfo
This class stores info we want to provide to or retain within an alias query.
Definition: AliasAnalysis.h:462
CommandLine.h
llvm::MemoryLocation::AATags
AAMDNodes AATags
The metadata nodes which describes the aliasing of the location (each member is null if that kind of ...
Definition: MemoryLocation.h:231
collectMDInDomain
static void collectMDInDomain(const MDNode *List, const MDNode *Domain, SmallPtrSetImpl< const MDNode * > &Nodes)
Definition: ScopedNoAliasAA.cpp:109
llvm::ScopedNoAliasAAResult::getModRefInfo
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, AAQueryInfo &AAQI)
Definition: ScopedNoAliasAA.cpp:75
llvm::PassRegistry::getPassRegistry
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Definition: PassRegistry.cpp:31
llvm::ScopedNoAliasAAWrapperPass::doFinalization
bool doFinalization(Module &M) override
doFinalization - Virtual method overriden by subclasses to do any necessary clean up after all passes...
Definition: ScopedNoAliasAA.cpp:173
InstrTypes.h
llvm::AnalysisUsage
Represent the analysis usage information of a pass.
Definition: PassAnalysisSupport.h:47
Domain
Domain
Definition: CorrelatedValuePropagation.cpp:710
llvm::ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass
ScopedNoAliasAAWrapperPass()
Definition: ScopedNoAliasAA.cpp:164
SmallPtrSet.h
ScopedNoAliasAA.h
llvm::CallingConv::ID
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
llvm::Instruction::getMetadata
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:279
getDomain
Domain getDomain(Value *V, LazyValueInfo *LVI, Instruction *CxtI)
Definition: CorrelatedValuePropagation.cpp:712
llvm::AAResultBase::alias
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, AAQueryInfo &AAQI)
Definition: AliasAnalysis.h:1222
llvm::cl::opt< bool >
llvm::ScopedNoAliasAAResult::alias
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, AAQueryInfo &AAQI)
Definition: ScopedNoAliasAA.cpp:54
MemoryLocation.h
llvm::AnalysisKey
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:69
llvm::cl::init
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:432
llvm::ModRefInfo
ModRefInfo
Flags indicating whether a memory access modifies or references memory.
Definition: AliasAnalysis.h:148
INITIALIZE_PASS
INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias-aa", "Scoped NoAlias Alias Analysis", false, true) ImmutablePass *llvm
Definition: ScopedNoAliasAA.cpp:157
llvm::Module
A Module instance is used to store all the information related to an LLVM module.
Definition: Module.h:65
llvm::MDNode
Metadata node.
Definition: Metadata.h:944
llvm::AliasResult::NoAlias
@ NoAlias
The two locations do not alias at all.
Definition: AliasAnalysis.h:99
llvm::AAResultBase::getModRefInfo
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, AAQueryInfo &AAQI)
Definition: AliasAnalysis.h:1244
llvm::ScopedNoAliasAAResult
A simple AA result which uses scoped-noalias metadata to answer queries.
Definition: ScopedNoAliasAA.h:29
llvm::AnalysisUsage::setPreservesAll
void setPreservesAll()
Set by analyses that do not transform their input at all.
Definition: PassAnalysisSupport.h:130
llvm::AAMDNodes::NoAlias
MDNode * NoAlias
The tag specifying the noalias scope.
Definition: Metadata.h:678
llvm::createScopedNoAliasAAWrapperPass
ImmutablePass * createScopedNoAliasAAWrapperPass()
Casting.h
llvm::ScopedNoAliasAA::run
ScopedNoAliasAAResult run(Function &F, FunctionAnalysisManager &AM)
Definition: ScopedNoAliasAA.cpp:150
llvm::ScopedNoAliasAAWrapperPass
Legacy wrapper pass to provide the ScopedNoAliasAAResult object.
Definition: ScopedNoAliasAA.h:65
llvm::SPIRV::FunctionParameterAttribute::NoAlias
@ NoAlias
llvm::AliasScopeNode
This is a simple wrapper around an MDNode which provides a higher-level interface by hiding the detai...
Definition: Metadata.h:1408
List
const NodeList & List
Definition: RDFGraph.cpp:199
llvm::SmallPtrSetImplBase::empty
LLVM_NODISCARD bool empty() const
Definition: SmallPtrSet.h:92
llvm::CallBase
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1174
llvm::SmallPtrSetImpl< const MDNode * >
llvm::AnalysisManager
A container for analyses that lazily runs them and caches their results.
Definition: InstructionSimplify.h:42
LLVMContext.h
InitializePasses.h
llvm::MDOperand
Tracking metadata reference owned by Metadata.
Definition: Metadata.h:773
llvm::ScopedNoAliasAAWrapperPass::ID
static char ID
Definition: ScopedNoAliasAA.h:69
llvm::MemoryLocation
Representation for a specific memory location.
Definition: MemoryLocation.h:210
llvm::ScopedNoAliasAAWrapperPass::getAnalysisUsage
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
Definition: ScopedNoAliasAA.cpp:178
llvm::SmallPtrSetImpl::insert
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:365