[CIR] Add basic thread-local storage (TLS) support #1996

lanza · 2025-11-20T21:57:13Z

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-> [CIR] Add basic thread-local storage (TLS) support #1996

This commit implements basic thread-local storage support in ClangIR:

Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface
to handle thread-local variable access in an ABI-specific way.
Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that:
- Accesses thread-local variables directly using their GlobalOp
- Relies on the 'tls_dyn' attribute on GlobalOp for TLS semantics
- Handles both value and reference types correctly
- Defers complex TLS wrapper function support to future work
Modified CIRGenExpr.cpp to call the ABI method instead of asserting
when encountering TLS_Dynamic variables.
Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving
global variable addresses.
Added comprehensive test coverage in thread-local.cpp that verifies:
- Basic thread_local variables with constant initialization
- GNU-style __thread variables - Function-local thread_local static variables
- Reading from and writing to thread_local variables
- Extern thread_local variable declarations
- Correct CIR generation with tls_dyn attribute
- Proper LLVM IR lowering to @llvm.threadlocal.address intrinsic

The implementation takes a simplified approach for now, relying on the
GlobalOp's thread_local attribute rather than generating wrapper functions.
This is sufficient for variables with trivial initialization. Future work
may add full wrapper function support for complex dynamic initialization.

[ghstack-poisoned]

This commit implements basic thread-local storage support in ClangIR: 1. Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface to handle thread-local variable access in an ABI-specific way. 2. Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that: - Accesses thread-local variables directly using their GlobalOp - Relies on the 'tls_dyn' attribute on GlobalOp for TLS semantics - Handles both value and reference types correctly - Defers complex TLS wrapper function support to future work 3. Modified CIRGenExpr.cpp to call the ABI method instead of asserting when encountering TLS_Dynamic variables. 4. Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving global variable addresses. 5. Added comprehensive test coverage in thread-local.cpp that verifies: - Basic thread_local variables with constant initialization - GNU-style __thread variables - Function-local thread_local static variables - Reading from and writing to thread_local variables - Extern thread_local variable declarations - Correct CIR generation with tls_dyn attribute - Proper LLVM IR lowering to llvm.threadlocal.address intrinsic The implementation takes a simplified approach for now, relying on the GlobalOp's thread_local attribute rather than generating wrapper functions. This is sufficient for variables with trivial initialization. Future work may add full wrapper function support for complex dynamic initialization. ghstack-source-id: 65ab4e1 Pull-Request: #1996

[ghstack-poisoned]

This commit implements basic thread-local storage support in ClangIR: 1. Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface to handle thread-local variable access in an ABI-specific way. 2. Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that: - Accesses thread-local variables directly using their GlobalOp - Relies on the 'tls_dyn' attribute on GlobalOp for TLS semantics - Handles both value and reference types correctly - Defers complex TLS wrapper function support to future work 3. Modified CIRGenExpr.cpp to call the ABI method instead of asserting when encountering TLS_Dynamic variables. 4. Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving global variable addresses. 5. Added comprehensive test coverage in thread-local.cpp that verifies: - Basic thread_local variables with constant initialization - GNU-style __thread variables - Function-local thread_local static variables - Reading from and writing to thread_local variables - Extern thread_local variable declarations - Correct CIR generation with tls_dyn attribute - Proper LLVM IR lowering to llvm.threadlocal.address intrinsic The implementation takes a simplified approach for now, relying on the GlobalOp's thread_local attribute rather than generating wrapper functions. This is sufficient for variables with trivial initialization. Future work may add full wrapper function support for complex dynamic initialization. ghstack-source-id: 2a8fafc Pull-Request: #1996

[ghstack-poisoned]

This commit implements thread-local storage support in ClangIR: 1. Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface to handle thread-local variable access in an ABI-specific way. 2. Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that: - Accesses thread-local variables using cir.get_global thread_local - Relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics - Handles both value and reference types correctly - Uses ClangIR's declarative approach instead of wrapper functions 3. Modified CIRGenExpr.cpp to call the ABI method for TLS_Dynamic variables. 4. Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving global variable addresses. 5. Added comprehensive test coverage in thread-local.cpp that verifies: - Basic thread_local variables with constant initialization - GNU-style __thread variables - Function-local thread_local static variables - Reading from and writing to thread_local variables - Extern thread_local variable declarations - Correct CIR generation with tls_dyn attribute - Proper LLVM IR lowering to llvm.threadlocal.address intrinsic ClangIR's approach differs from traditional CodeGen: instead of creating wrapper functions (_ZTW*) in the IR, ClangIR marks GlobalOps with tls_dyn and relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics. This achieves correct TLS semantics while maintaining ClangIR's higher-level representation. ghstack-source-id: d912c08 Pull-Request: #1996

[ghstack-poisoned]

This commit implements thread-local storage support in ClangIR: 1. Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface to handle thread-local variable access in an ABI-specific way. 2. Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that: - Accesses thread-local variables using cir.get_global thread_local - Relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics - Handles both value and reference types correctly - Uses ClangIR's declarative approach instead of wrapper functions 3. Modified CIRGenExpr.cpp to call the ABI method for TLS_Dynamic variables. 4. Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving global variable addresses. 5. Added comprehensive test coverage in thread-local.cpp that verifies: - Basic thread_local variables with constant initialization - GNU-style __thread variables - Function-local thread_local static variables - Reading from and writing to thread_local variables - Extern thread_local variable declarations - Correct CIR generation with tls_dyn attribute - Proper LLVM IR lowering to llvm.threadlocal.address intrinsic ClangIR's approach differs from traditional CodeGen: instead of creating wrapper functions (_ZTW*) in the IR, ClangIR marks GlobalOps with tls_dyn and relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics. This achieves correct TLS semantics while maintaining ClangIR's higher-level representation. ghstack-source-id: 267f175 Pull-Request: #1996

bcardosolopes

Overall good, thanks! Some nits and ready to go

bcardosolopes · 2025-11-20T23:29:40Z

clang/lib/CIR/CodeGen/CIRGenCXXABI.h

  // directly or require access through a thread wrapper function.
  virtual bool usesThreadWrapperFunction(const VarDecl *VD) const = 0;

+  virtual LValue EmitThreadLocalVarDeclLValue(CIRGenFunction &CGF,


camelBack here and everyelse it makes sense

bcardosolopes · 2025-11-20T23:29:54Z

clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp

    return !isEmittedWithConstantInitializer(VD) || mayNeedDestruction(VD);
  }

+  LValue EmitThreadLocalVarDeclLValue(CIRGenFunction &CGF, const VarDecl *VD,


bcardosolopes · 2025-11-20T23:31:06Z

clang/lib/CIR/CodeGen/CIRGenModule.h

  llvm::DenseSet<clang::GlobalDecl> DiagnosedConflictingDefinitions;

+  /// thread_local variables defined or used in this TU.
+  std::vector<const clang::VarDecl *> CXXThreadLocals;


this should be lowercase too!

[ghstack-poisoned]

This commit implements thread-local storage support in ClangIR: 1. Added EmitThreadLocalVarDeclLValue() method to CIRGenCXXABI interface to handle thread-local variable access in an ABI-specific way. 2. Implemented EmitThreadLocalVarDeclLValue() in CIRGenItaniumCXXABI that: - Accesses thread-local variables using cir.get_global thread_local - Relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics - Handles both value and reference types correctly - Uses ClangIR's declarative approach instead of wrapper functions 3. Modified CIRGenExpr.cpp to call the ABI method for TLS_Dynamic variables. 4. Added CIRGenModule::getAddrOfGlobalVar() helper for retrieving global variable addresses. 5. Added comprehensive test coverage in thread-local.cpp that verifies: - Basic thread_local variables with constant initialization - GNU-style __thread variables - Function-local thread_local static variables - Reading from and writing to thread_local variables - Extern thread_local variable declarations - Correct CIR generation with tls_dyn attribute - Proper LLVM IR lowering to llvm.threadlocal.address intrinsic ClangIR's approach differs from traditional CodeGen: instead of creating wrapper functions (_ZTW*) in the IR, ClangIR marks GlobalOps with tls_dyn and relies on LLVM lowering to insert @llvm.threadlocal.address intrinsics. This achieves correct TLS semantics while maintaining ClangIR's higher-level representation. ghstack-source-id: 0a94a40 Pull-Request: #1996

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lanza requested review from andykaylor, bcardosolopes and xlauko as code owners November 20, 2025 21:57

lanza mentioned this pull request Nov 20, 2025

[CIR] Add support for CK_AtomicToNonAtomic casts #1989

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[CIR] Add basic thread-local storage (TLS) support #1996

[CIR] Add basic thread-local storage (TLS) support #1996

lanza commented Nov 20, 2025 •

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lanza commented Nov 20, 2025 •

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