Re: [PATCH 02/17] [APX NDD] Restrict TImode register usage when NDD enabled

[Hongyu Wang <wwwhhhyyy333@gmail.com>]

Uros Bizjak <ubizjak@gmail.com> 于2023年12月5日周二 18:46写道：

>
> On Tue, Dec 5, 2023 at 3:29 AM Hongyu Wang <hongyu.wang@intel.com> wrote:
> >
> > Under APX NDD, previous TImode allocation will have issue that it was
> > originally allocated using continuous pair, like rax:rdi, rdi:rdx.
> >
> > This will cause issue for all TImode NDD patterns. For NDD we will not
> > assume the arithmetic operations like add have dependency between dest
> > and src1, then write to 1st highpart rdi will be overrided by the 2nd
> > lowpart rdi if 2nd lowpart rdi have different src as input, then the write
> > to 1st highpart rdi will missed and cause miscompliation.
> >
> > To resolve this, under TARGET_APX_NDD we'd only allow register with even
> > regno to be allocated with TImode, then TImode registers will be allocated
> > with non-overlapping pairs.
>
> Perhaps you could use earlyclobber with __doubleword instructions:
>
> (define_insn_and_split "*add<dwi>3_doubleword"
>   [(set (match_operand:<DWI> 0 "nonimmediate_operand" "=ro,r")
>     (plus:<DWI>
>       (match_operand:<DWI> 1 "nonimmediate_operand" "%0,0")
>       (match_operand:<DWI> 2 "x86_64_hilo_general_operand" "r<di>,o")))
>    (clobber (reg:CC FLAGS_REG))]
>
> For the above pattern, you can add earlyclobbered &r output
> alternative that guarantees that output won't be allocated to any of
> the input registers.
>

Yes, it does resolve the dest/src overlapping issue we met, thanks!
I tried it and no fails in gcc-testsuite and spec. Suppose for
different src1/src2 RA can handle them correctly.

Will update in V3 patches with the changes of get_attr_isa (insn) == ISA_APX_NDD