[libc-commits] [libc] [libc] Keep headers compatible with -std=c89 mode (PR #121981)

[via libc-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Roland McGrath (frobtech)

<details>
<summary>Changes</summary>

C89 doesn't have the `restrict` keyword.  When in `-std=c89`
mode, GNU-compatible compilers require the `__restrict` spelling.


---
Full diff: https://github.com/llvm/llvm-project/pull/121981.diff


1 Files Affected:

- (modified) libc/include/__llvm-libc-common.h (+8-1) 


``````````diff
diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
index d9d70aff771c08..c63eb134a5e5d7 100644
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -50,7 +50,14 @@
 #define __END_C_DECLS
 
 #undef __restrict
-#define __restrict restrict // C99 and above support the restrict keyword.
+#if __STDC_VERSION__ >= 199901L
+// C99 and above support the restrict keyword.
+#define __restrict restrict
+#elif !defined(__GNUC__)
+// GNU-compatible compilers accept the __ spelling in all modes.
+// Otherwise, omit the qualifier for pure C89 compatibility.
+#define __restrict
+#endif
 
 #undef _Noreturn
 #if __STDC_VERSION__ >= 201112L

``````````

</details>


https://github.com/llvm/llvm-project/pull/121981