On Sun, Jan 16, 2022 at 12:44 AM Uros Bizjak via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Sat, Jan 15, 2022 at 5:39 PM Hongyu Wang <wwwhhhyyy...@gmail.com> wrote:
> >
> > Thanks for the suggestion, here is the updated patch that survived
> > bootstrap/regtest.
>
> LGTM for me, but please get the final approval from Hongtao.
>
Ok, thanks.
> Thanks,
> Uros.
>
> > > Please note reg_mentioned_p in the above condition. This function
> > > returns nonzero if register op0 appears somewhere within op1 and is
> > > critical for the correct operation of your patch.
> > I added reg_mentioned_p for all insns except fp16 complex mult, since
> > they have constraint & to the dest so it must be allocated different
> > register from src.
> >
> > Uros Bizjak <ubiz...@gmail.com> 于2022年1月14日周五 23:49写道：
> >
> >
> > >
> > > On Fri, Jan 14, 2022 at 2:44 PM Hongyu Wang <wwwhhhyyy...@gmail.com>
> > > wrote:
> > > >
> > > > > Are there any technical obstacles to introduce subst to
> > > > > define_{,insn_and_}split?
> > > >
> > > > gccint says: define_subst can be used only in define_insn and
> > > > define_expand, it cannot be used in other expressions (e.g. in
> > > > define_insn_and_split).
> > >
> > > Hm, hm ... annoying ...
> > >
> > > > I have no idea how to implement it in current infrastructure.
> > > >
> > > > > In the proposed patch, if the output register is also mentioned in the
> > > > > input, then clearing before insn will clear the value in the input
> > > > > register. The solution in the i386.md also takes care of this issue.
> > > > >
> > > >
> > > > For this, I think we can add REGNO checks for operands in condition
> > > > (which means there is true dependency).
> > >
> > > Let's go in your direction, considering the limitations of current
> > > infrastructure.
> > > +{
> > > + if (TARGET_DEST_FALSE_DEPENDENCY
> > > + && get_attr_dest_false_dep (insn) ==
> > > + DEST_FALSE_DEP_TRUE)
> > > + output_asm_insn ("vxorps\t{%x0, %x0, %x0}", operands);
> > > + return "vgetmant<ssemodesuffix>\t{%2, <round_saeonly_mask_op3>%1,
> > > %0<mask_operand3>|%0<mask_operand3>, %1<round_saeonly_mask_op3>, %2}";
> > > +}
> > >
> > > There is no need to pass the information via attributes. IMO, you
> > > shoud use subst attribute directly in the condition:
> > >
> > > {
> > > if (TARGET_DEST_FALSE_DEPENDENCY
> > > && <mask3_dest_false_dep_attr>
> > > && !reg_mentioned_p (operands[0], operands[1]))
> > > output_asm_insn ("vxorps\t{%x0, %x0, %x0}", operands);
> > > return ".....";
> > > }
> > >
> > > Assume the above works, so please:
> > >
> > > - rename TARGET_DEST_FALSE_DEPENDENCY to something less generic, maybe
> > > following existing BMI example with TARGET_AVOID_FALSE_DEP_FOR_AVX512F
> > > - rename "mask3_dest_false_dep_attr" to "mask3_false_dep_for_avx512f_cond"
> > >
> > > Please note reg_mentioned_p in the above condition. This function
> > > returns nonzero if register op0 appears somewhere within op1 and is
> > > critical for the correct operation of your patch.
> > >
> > > Uros.
--
BR,
Hongtao
