Re: [PATCH] sched: Optimize __calc_delta.

[Peter Zijlstra]

On Tue, Mar 02, 2021 at 12:57:37PM -0800, Josh Don wrote:
> On gcc, the asm versions of `fls` are about the same speed as the
> builtin. On clang, the versions that use fls (fls,fls64) are more than
> twice as slow as the builtin. This is because the way the `fls` function
> is written, clang puts the value in memory:
> https://godbolt.org/z/EfMbYe. This can be fixed in a separate patch.

Is this because clang gets the asm constraints wrong? ISTR that
happening before, surely the right thing is to fix clang?