Hi Suwa-san,
On Mon, Jan 23, 2023 at 7:43 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 ;; No '0' in the source constraints
> ;; The destination replaced is
> ;; irrelevant to the sources if the
> ;; destination constraint has '&'
> ;; 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.c: New.
> ---
> gcc/config/xtensa/xtensa.md | 49 +++++++++++++++++++
> .../gcc.target/xtensa/elim_GP_regmove.c | 23 +++++++++
> 2 files changed, 72 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_GP_regmove.c
This change breaks windowed builds by the following ICEs:
libgcc/libgcov-interface.c: In function ‘__gcov_execlp’:
libgcc/libgcov-interface.c:263:1: error: insn does not satisfy its constraints:
263 | }
| ^
(insn 96 95 98 11 (set (reg/f:SI 1 sp)
(minus:SI (reg/f:SI 1 sp)
(reg:SI 8 a8 [85]))) "libgcc/libgcov-interface.c":253:20 4 {subsi3}
(expr_list:REG_DEAD (reg:SI 8 a8 [85])
(nil)))
during RTL pass: cprop_hardreg
libgcc/libgcov-interface.c:263:1: internal compiler error: in
extract_constrain_insn, at recog.cc:2692
It also introduces at least one regression in executable tests
in call0 build, I haven't tracked it down yet.
--
Thanks.
-- Max
