On Mon, Jun 13, 2022 at 8:54 PM Takayuki 'January June' Suwa
<jjsuwa_sys3...@yahoo.co.jp> wrote:
>
> RTL expansion of substitution to [DS]Cmode hard register includes obstructive
> register clobber.
>
> A simplest example:
>
> double _Complex test(double _Complex c) {
> return c;
> }
>
> will be converted to:
>
> (set (reg:DF 42 [ c ]) (reg:DF 2 a2))
> (set (reg:DF 43 [ c+8 ]) (reg:DF 4 a4))
> (clobber (reg:DC 2 a2))
> (set (reg:DF 2 a2) (reg:DF 42 [ c ]))
> (set (reg:DF 4 a4) (reg:DF 43 [ c+8 ]))
> (use (reg:DC 2 a2))
> (return)
>
> and then finally:
>
> test:
> mov a8, a2
> mov a9, a3
> mov a6, a4
> mov a7, a5
> mov a2, a8
> mov a3, a9
> mov a4, a6
> mov a5, a7
> ret
>
> As you see, it is so ridiculous.
>
> This patch eliminates such clobber in order to prune away the wasted move
> instructions by the optimizer:
>
> test:
> ret
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.md (DSC): New split pattern and mode iterator.
> ---
> gcc/config/xtensa/xtensa.md | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
--
Thanks.
-- Max
