Re: [PATCH v5] xtensa: Eliminate unnecessary general-purpose reg-reg moves

[Max Filippov <jcmvbkbc@gmail.com>]

On Fri, Feb 17, 2023 at 8:43 PM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> Register-register move instructions that can be easily seen as
> unnecessary by the human eye may remain in the compiled result.
> For example:
>
> /* example */
> double test(double a, double b) {
>   return __builtin_copysign(a, b);
> }
>
> test:
>         add.n   a3, a3, a3
>         extui   a5, a5, 31, 1
>         ssai    1
>                                 ;; Be in the same BB
>         src     a7, a5, a3      ;; Replacing the destination doesn't
>                                 ;;   violate any constraints of the
>                                 ;;   operands
>                                 ;; No CALL insns in this span
>                                 ;; Both A3 and A7 are irrelevant to
>                                 ;;   insns in this span
>         mov.n   a3, a7          ;; An unnecessary reg-reg move
>                                 ;; A7 is not used after this
>         ret.n
>
> The last two instructions above, excluding the return instruction,
> could be done like this:
>
>         src     a3, a5, a3
>
> This symptom often occurs when handling DI/DFmode values with SImode
> instructions.  This patch solves the above problem using peephole2
> pattern.
>
> gcc/ChangeLog:
>
>         * config/xtensa/xtensa.md: New peephole2 pattern that eliminates
>         the occurrence of general-purpose register used only once and for
>         transferring intermediate value.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/xtensa/elim_GP_regmove_[01].c: New.
> ---
>  gcc/config/xtensa/xtensa.md                   | 46 +++++++++++++++++++
>  .../gcc.target/xtensa/elim_GP_regmove_0.c     | 23 ++++++++++
>  .../gcc.target/xtensa/elim_GP_regmove_1.c     | 10 ++++
>  3 files changed, 79 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_0.c
>  create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_1.c

Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.

-- 
Thanks.
-- Max