Re: [PATCH] aarch64: add single instruction math functions

[David Edelsohn <dje.gcc@gmail.com>]

On Sun, Mar 19, 2017 at 11:05 AM, Rich Felker <dalias@libc.org> wrote:
> On Sun, Mar 19, 2017 at 08:55:58AM -0400, David Edelsohn wrote:
>> I thought that the goal of musl was "Minimal machine-specific code".
>
> My interpretation of minimal is two-fold:
>
> - minimal amount of arch-specific coding required to bring up a new
>   arch.
>
> - when arch-specific code is present by necessity or for optimization
>   (speed or size), keeping complexity, maintenance cost, and room for
>   arch-specific bugs minimal.
>
> This is not intended to preclude use of single-instruction primitives
> (see existing code for x86, etc.) for math functions or even critical
> things that may be somewhat more complex like memcpy.

This policy makes maintenance more difficult and bugs more difficult
to analyze because different ports of musl libc may use less common
code.

Single instruction primitives occur more often in CISC architectures
by definition, so this preferences CISC.

This policy makes the decision process for architecture-specific
changes much more arbitrary.

- David