On Wed, Aug 17, 2022 at 12:32 PM Takayuki 'January June' Suwa
<jjsuwa_sys3...@yahoo.co.jp> wrote:
>
> This patch enforces the use of "addmi" machine instruction instead of
> addition/subtraction with two source registers for adjusting the stack
> pointer, if the adjustment fits into a signed 16-bit and is also a multiple
> of 256.
>
> /* example */
> void test(void) {
> char buffer[4096];
> __asm__(""::"m"(buffer));
> }
>
> ;; before
> test:
> movi.n a9, 1
> slli a9, a9, 12
> sub sp, sp, a9
> movi.n a9, 1
> slli a9, a9, 12
> add.n sp, sp, a9
> addi sp, sp, 0
> ret.n
>
> ;; after
> test:
> addmi sp, sp, -0x1000
> addmi sp, sp, 0x1000
> ret.n
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.cc (xtensa_expand_prologue):
> Use an "addmi" machine instruction for updating the stack pointer
> rather than addition/subtraction via hard register A9, if the amount
> of change satisfies the literal value conditions of that instruction
> when the CALL0 ABI is used.
> (xtensa_expand_epilogue): Ditto.
> And also inhibit the stack pointer addition of constant zero.
> ---
> gcc/config/xtensa/xtensa.cc | 79 +++++++++++++++++++++++++------------
> 1 file changed, 54 insertions(+), 25 deletions(-)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
--
Thanks.
-- Max
