* H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 01/19/2015 02:04 AM, Peter Zijlstra wrote:
> > On Mon, Jan 19, 2015 at 07:54:22AM +1200, Linus Torvalds wrote:
> >> Why?
> >>
> >> The 8- and 16- bit versions are the same as the 32-bit one.
> >> This seems pointless. If you want something where the sign
> >> is in bit 3, they all return the same value, just the return
> >> type differs, but that's really a *caller* thing, no?
> >
> > Even for the 8bit ones? Since we have the *H and *L register
> > we have more 8 bit regs than we have 16/32 bit regs and it
> > might just be worth it.
>
> Fewer, actually. gcc doesn't really use the H registers much,
Is that true for other compilers as well?
> and instead considers 8-bit values to occupy the whole
> register, but that means only four are available in 32-bit
> mode.
So where are we with this? Should I consider:
7e9358073d3f ("bitops: Add sign_extend8(), 16 and 64 functions")
NAK-ed due to having marginal benefits, or due to having no
benefits whatsoever?
How about the two patch series from Martin Keppling - that does
seem to be both beneficial and correct, agreed?
Thanks,
Ingo
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