Hi Suwa-san,
On Wed, Jan 18, 2023 at 9:06 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
> ;; 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/config/xtensa/xtensa.md | 45 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
With this change I see the following ICEs:
in the libgcc build:
gcc/libgcc/libgcov-interface.c: In function ‘__gcov_execl’:
gcc/libgcc/libgcov-interface.c:228:1: error: insn does not satisfy its
constraints:
228 | }
| ^
(insn 96 95 98 11 (set (reg/f:SI 1 sp)
(minus:SI (reg/f:SI 1 sp)
(reg:SI 8 a8 [85])))
"gcc/libgcc/libgcov-interface.c":218:20 4 {subsi3}
(expr_list:REG_DEAD (reg:SI 8 a8 [85])
(nil)))
during RTL pass: cprop_hardreg
--------------------
in the linux kernel build:
linux/lib/find_bit.c: In function ‘_find_next_bit’:
linux/lib/find_bit.c:70:1: error: unrecognizable insn:
70 | }
| ^
(insn 74 72 75 16 (set (reg:SI 10 a10)
(asm_operands:SI ("ssai 8
srli %0, %1, 16
src %0, %0, %1
src %0, %0, %0
src %0, %1, %0
") ("=&a") 0 [
(reg/v:SI 10 a10 [orig:59 res ] [59])
]
[
(asm_input:SI ("a") linux/arch/xtensa/include/uapi/asm/swab.h:24)
]
[] linux/arch/xtensa/include/uapi/asm/swab.h:24))
"linux/arch/xtensa/include/uapi/asm/swab.h":24:5 -1
(nil))
during RTL pass: cprop_hardreg
linux/lib/find_bit.c:70:1: internal compiler error: in
extract_constrain_insn, at recog.cc:2692
0x6c3214 _fatal_insn(char const*, rtx_def const*, char const*, int, char const*)
gcc/gcc/rtl-error.cc:108
0x6c3297 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
gcc/gcc/rtl-error.cc:116
0x6b4735 extract_constrain_insn(rtx_insn*)
gcc/gcc/recog.cc:2692
0xe1f67e copyprop_hardreg_forward_1
gcc/gcc/regcprop.cc:826
0xe20a0f execute
gcc/gcc/regcprop.cc:1408
--
Thanks.
-- Max
