Deduplicate minipal thread ID TLS cache.

[lateralusX]

Summary

Deduplicate the TLS cache used by minipal_get_current_thread_id.

Fixes #131954.

Root cause

minipal_get_current_thread_id previously declared its cached thread ID as a function-local static thread_local variable in thread.h.

Because the function has internal linkage, each translation unit using it could emit a separate 8-byte TLS slot. Enabling the in-process crash reporter added another consumer, increasing libcoreclr.so's TLS footprint enough to exceed glibc's optional static TLS allocation on Linux ARM64.

This caused glibc to resolve CoreCLR TLS accesses through _dl_tlsdesc_dynamic instead of _dl_tlsdesc_return, adding overhead to allocation, thread-static access, and other common runtime paths.

Changes

• Move the cached thread ID into a single minipal compilation unit.
• Externally declare the shared TLS variable from thread.h.
• Use a common macro for the C and C++ TLS storage-class spellings.

Validation

A test with two independent C and C++ translation units showed:

• Before: two local 8-byte TLS slots and a 16-byte TLS segment.
• After: one shared 8-byte TLS slot.
• GCC C++ emits no TLS dynamic-initialization relocation for the shared variable.

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[Copilot]

Pull request overview

Deduplicates the TLS-backed cache used by minipal_get_current_thread_id() by moving the cached thread ID out of a function-local TLS and into a single TLS variable defined in a dedicated minipal compilation unit.

Changes:

• Introduces MINIPAL_THREAD_LOCAL and uses it to declare a shared TLS variable minipal_cached_thread_id in thread.h.
• Adds thread.c to define minipal_cached_thread_id (under the same WASM/reentrancy guards).
• Updates minipal’s CMake source list to compile thread.c on Unix hosts.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/native/minipal/thread.h	Switches the cache from a function-local TLS static to an extern TLS variable and adds a TLS macro.
src/native/minipal/thread.c	Defines the shared TLS variable so all translation units refer to the same TLS slot.
src/native/minipal/CMakeLists.txt	Ensures thread.c is built into minipal on Unix.

[EgorBo]

@EgorBot -linux_arm64 --filter "System.Tests.Perf_UInt16.Parse*"

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[AndyAyersMS]

For some reason egorbot failed on main, but passed on the PR

Method	Toolchain	value	Mean	Error	Ratio	Allocated	Alloc Ratio
Parse	/main/corerun	0	NA	NA	?	NA	?
Parse	/PR_131991/corerun	0	5.631 ns	0.0008 ns	1.00	-	NA
Parse	/main/corerun	12345	NA	NA	?	NA	?
Parse	/PR_131991/corerun	12345	8.717 ns	0.0013 ns	1.00	-	NA
Parse	/main/corerun	65535	NA	NA	?	NA	?
Parse	/PR_131991/corerun	65535	8.852 ns	0.0014 ns	1.00	-	NA

PR results look similar to the fast "before" results we have from the lab

[jkotas]

Isn't the actual problem that this is static inline method? static means that each compilation unit gets its own copy of the code. Methods in headers should be inline, but not static - static methods in headers are a recipe to produce undesirable code duplication.