Re: [PATCH] Extend 64-bit vector bit_op patterns with ?r alternative

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Jul 14, 2022 at 3:22 PM Uros Bizjak via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Jul 14, 2022 at 7:33 AM liuhongt <hongtao.liu@intel.com> wrote:
> >
> > And split it to GPR-version instruction after reload.
> >
> > > ?r was introduced under the assumption that we want vector values
> > > mostly in vector registers. Currently there are no instructions with
> > > memory or immediate operand, so that made sense at the time. Let's
> > > keep ?r until logic instructions with mem/imm operands are introduced.
> > > So, for the patch that adds 64-bit vector logic in GPR, I would advise
> > > to first introduce only register operands. mem/imm operands should be
> > Update patch to add ?r to 64-bit bit_op patterns.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > No big imact on SPEC2017(Most same binary).
>
> The problem with your approach is with the combine pass, where combine
> first tries to recognize the combined instruction without clobber,
> before re-recognizing instruction with added clobber. So, if a forward
> propagation happens, the combine will *always* choose the insn variant
> without GPR.
Thank you for the explanation, I really did not know this point.
>
> So, the solution with VI_16_32 is to always expand with a clobbered
> version that is split to either SImode or V16QImode. With 64-bit
> instructions, we have two additional complications. First, we have a
> native MMX instruction, and we have to split to it after reload, and
> second, we have a builtin that expects vector insn.
>
> To solve the first issue, we should change the mode of
> "*mmx<code><mode>" to V1DImode and split your new _gpr version with
> clobber to it for !GENERAL_REG_P operands.
>
> The second issue could be solved by emitting V1DImode instructions
> directly from the expander. Please note there are several expanders
> that expect non-clobbered logic insn in certain mode to be available,
> so the situation can become quite annoying...
Yes. It looks like it would add a lot of code complexity, I'll hold
the patch for now.
>
> Uros.



-- 
BR,
Hongtao