On Fri, Feb 17, 2023 at 8:43 PM Takayuki 'January June' Suwa
<jjsuwa_sys3...@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
