[libc-commits] [libc] [libc][docs] codify Policy on Assembler Sources (PR #88185)

[Nick Desaulniers via libc-commits]

================
@@ -186,3 +186,32 @@ We expect contributions to be free of warnings from the `minimum supported
 compiler versions`__ (and newer).
 
 .. __: https://libc.llvm.org/compiler_support.html#minimum-supported-versions
+
+Policy on Assembler sources
+===========================
+
+Coding in high level languages such as C++ provides benefits relative to low
+level languages like Assembler, such as:
+
+* Improved safety
+* Instrumentation
+
+  * Code coverage
+  * Profile collection
+* Sanitization
+* Debug info
+
+While its not impossible to have Assembler code that correctly provides all of
+the above, we do not wish to maintain such Assembler sources in llvm-libc.
+
+That said, there a few functions provided by llvm-libc that are more difficult
+to implement or maintain in C++ than Assembler. We do use inline or out-of-line
+Assembler in an intentionally minimal set of places; typically places where the
+stack or individual register state must be manipulated very carefully for
+correctness.
+
+Contributions adding Assembler for performance are not welcome. Contributors
----------------
nickdesaulniers wrote:

Thanks all for the feedback.  I've updated this in 0749f082f33b30fb3fdd5f8888177c4ade17dd6b. PTAL.

I now mention:
- > instances where a specific instruction sequence does not have a corresponding compiler builtin function today.
- > Contributions adding functions implemented purely in Assembly for performance are not welcome.
- > Ideally, bugs should be filed against compiler vendors, and links to those bug reports should appear in commit messages or comments that seek to add Assembly to llvm-libc.
- > Patches containing any amount of Assembly ideally should be approved by 2 maintainers.

https://github.com/llvm/llvm-project/pull/88185