Re: [PATCH] sched: Optimize __calc_delta.

[Josh Don]

On Wed, Mar 3, 2021 at 2:02 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> 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?

https://bugs.llvm.org/show_bug.cgi?id=49406 filed