[libc] Change LIBC_THREAD_LOCAL to be dependent on LIBC_THREAD_MODE

[saturn691]

When single-threaded mode is selected, all instances of the keyword LIBC_THREAD_LOCAL are stubbed out, similar to how it currently works on the GPU. This allows baremetal builds to avoid using thread_local.

However, libcxx uses shared headers, so we need to be careful there. Thankfully, there is already an option to disable multithreading in libcxx, so a flag is added such that single-threaded mode is propagated down to libc.

[llvmbot]

@llvm/pr-subscribers-libc

Author: William Huynh (saturn691)

Changes

This allows baremetal builds to avoid using thread_local. However, libcxx may be affected by this.

---

Full diff: https://github.com/llvm/llvm-project/pull/151527.diff

1 Files Affected:

• (modified) libc/src/__support/macros/attributes.h (+1-1)

diff --git a/libc/src/__support/macros/attributes.h b/libc/src/__support/macros/attributes.h
index c6474673de85a..23f973827b6f9 100644
--- a/libc/src/__support/macros/attributes.h
+++ b/libc/src/__support/macros/attributes.h
@@ -28,7 +28,7 @@
 #define LIBC_INLINE_ASM __asm__ __volatile__
 #define LIBC_UNUSED __attribute__((unused))
 
-#ifdef LIBC_TARGET_ARCH_IS_GPU
+#if LIBC_THREAD_MODE == LIBC_THREAD_MODE_SINGLE
 #define LIBC_THREAD_LOCAL
 #else
 #define LIBC_THREAD_LOCAL thread_local

[saturn691]

It seems the CI failure here stems from a manual interrupt- requesting review.