[mborland]

Currently, GNU __thread variable templates are given static storage duration instead of thread storage duration. This PR fixes this.

Closes: #536

Summary by CodeRabbit

• Bug Fixes
  • GNU __thread variable-template instances now behave as thread-local variables, with separate storage and initialization for each thread.
  • Corrected C23 code generation for file-scope __thread variables with internal linkage.
  • Improved diagnostics for thread-local variable templates with dynamic initialization or addresses used in constant expressions.
• Documentation
  • Added guidance and examples covering thread-local variable templates and related diagnostics.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The compiler now propagates GNU __thread to variable-template instances and checks their declaration modifiers. C23 generated-C handling recognizes these variables as thread-local. New regression tests cover thread isolation, specializations, dynamic initialization diagnostics, and constant-expression address use.

Changes: GNU thread-local variable templates

Layer / File(s)	Summary
Template modifier propagation and checks src/decls.c, src/decls.h, src/templates.c	The declaration-modifier check is available outside src/decls.c. Variable-template processing copies DM_THREAD to instances, checks initialization against declaration modifiers, and clears the modifier on a specialization’s first declaration.
C23 generated-C handling src/c_gen_be.c	File-scope variable selection recognizes DM_THREAD when the relevant declaration-modifier and TLS-specifier options are enabled. It omits non-extern thread-local variables from the non-defining pass and includes them in the definition pass.
Regression tests and issue note tests/tests/regressions/gh-536*.sft.cpp, tests/tests/regressions/.gh-536*.rto/*, src/pending_changes/gh-536-thread-variable-template.txt	Regression tests cover thread-local instance behavior, specializations, dynamic initialization diagnostics, and constant-expression address use. Test fixtures record GCC and Clang runs. The issue note describes the C23 code-generation case.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: daveedvdv-nvidia, wchilders-nvidia

Merge Risk: Minimal · up to 3fc37

The change makes GNU __thread variable-template instances thread-local, adds C23 generated-C handling for them, and adds regression tests for runtime and diagnostic behavior. No concrete merge-blocking defect was found in the reviewed changes.

Pre-merge checks: 4

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title says the change makes GNU __thread variable templates thread local, and [GH #536] names the linked issue. The changeset matches this. The templates.c change copies DM_THREAD onto variable-te…
Linked Issues check		[#536] Requirement: instances of GNU __thread variable templates must have thread storage duration. The reviewed summary shows that src/templates.c copies the DM_THREAD modifier, recorded during…
Out of Scope Changes check		All listed changes support the #536 fix. src/c_gen_be.c and src/templates.c implement the thread-local handling. src/decls.c and src/decls.h change check_variable_decl_modifiers from file-lo…

Full details: Title check

Explanation

The title says the change makes GNU __thread variable templates thread local, and [GH #536] names the linked issue. The changeset matches this. The templates.c change copies DM_THREAD onto variable-template instances, the C23 code generation in c_gen_be.c handles __thread file-scope variables, and the new gh-536 regression tests check distinct per-thread addresses. The title is specific and concise, so it passes.

Full details: Linked Issues check

Explanation

[#536] Requirement: instances of GNU __thread variable templates must have thread storage duration. The reviewed summary shows that src/templates.c copies the DM_THREAD modifier, recorded during declaration rescan, onto variable-template instances when thread-local storage specifiers are supported. src/c_gen_be.c adds is_thread_local_in_generated_c, which treats DM_THREAD as thread-local, so __thread declarations get the same file-scope handling as thread_local declarations. This addresses the C back-end cause named in the issue. tests/tests/regressions/gh-536.sft.cpp checks that each tested thread-local instance has a distinct address per thread, starts with its expected value, and keeps modifications local to the thread. The explicit tv<long> specialization is documented as shared, which matches normal explicit-specialization semantics. Automated test coverage exists. This assessment relies on the AI-generated summary and the listed changes; I did not inspect the diff hunks directly, so the exact code paths are not independently verified.

Full details: Out of Scope Changes check

Explanation

All listed changes support the #536 fix. src/c_gen_be.c and src/templates.c implement the thread-local handling. src/decls.c and src/decls.h change check_variable_decl_modifiers from file-local to external linkage, with a no-op macro when DECL_MODIFIERS_IN_USE is disabled. This exposes the helper needed by templates.c and is a supporting change. The added diagnostics for dynamic initialization of thread-local template variables and for taking an instance address in a constant expression are checked by the negative regression tests. These diagnostics follow from thread-local semantics that the issue's thread_local behavior already defines. The pending-changes note and the regression fixtures document and test the change. No unrelated change is identified in the summary.

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Recent review info

Run configuration

• Source mode: Auto
• Repository: edgcpp/compiler
• Branch: main
• File: .coderabbit.yaml
• Commit: cd21a3e
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Advanced
• Run ID: 18cfc849-bae8-4963-aaf9-5cbd2ed4785d

Commits

Reviewing files that changed from the base of the PR and between cd21a3e and 3fc3755.

Files selected for processing: 15

• src/c_gen_be.c
• src/decls.c
• src/decls.h
• src/pending_changes/gh-536-thread-variable-template.txt
• src/templates.c
• tests/tests/regressions/.gh-536-negative.rto/default.1.1.txt
• tests/tests/regressions/.gh-536-negative.rto/default.2.1.txt
• tests/tests/regressions/.gh-536.rto/default.1.1.txt
• tests/tests/regressions/.gh-536.rto/default.1.2.txt
• tests/tests/regressions/.gh-536.rto/default.2.1.txt
• tests/tests/regressions/.gh-536.rto/default.2.2.txt
• tests/tests/regressions/.gh-536.rto/default.3.1.txt
• tests/tests/regressions/.gh-536.rto/default.3.2.txt
• tests/tests/regressions/gh-536-negative.sft.cpp
• tests/tests/regressions/gh-536.sft.cpp

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 3 remain after this review.

[edgcpp-bot]

AcknowlEDG review results updated for 3fc37557739f:

• Test - Changes (new)

[edgcpp-bot]

AcknowlEDG review results updated for 3fc37557739f:

• Bench - C (new)
• Bench - C++ (new)
• Test - Changes (unchanged)

CI success.