On Sat, May 10, 2025 at 12:51 PM Takayuki 'January June' Suwa
<jjsuwa_sys3...@yahoo.co.jp> wrote:
>
> Until now (presumably after transition to LRA), hard registers storing
> function arguments or return values were spilling undesirably when
> TARGET_HARD_FLOAT is enabled.
>
> /* example */
> float test0(float a, float b) {
> return a + b;
> }
> extern float foo(void);
> float test1(void) {
> return foo() * 3.14f;
> }
>
> ;; before
> test0:
> entry sp, 48
> wfr f0, a2
> wfr f1, a3
> add.s f0, f0, f1
> s32i.n a2, sp, 0 ;; unwanted spilling-out
> s32i.n a3, sp, 4 ;;
> rfr a2, f0
> retw.n
> .literal .LC1, 1078523331
> test1:
> entry sp, 48
> call8 foo
> l32r a8, .LC1
> wfr f0, a10
> wfr f1, a8
> mul.s f0, f0, f1
> s32i.n a10, sp, 0 ;; unwanted spilling-out
> rfr a2, f0
> retw.n
>
> Ultimately, that is because the costs of moving between integer and
> floating-point hard registers are undefined and the default (large value)
> is used. This patch fixes this.
>
> ;; after
> test0:
> entry sp, 32
> wfr f1, a2
> wfr f0, a3
> add.s f0, f1, f0
> rfr a2, f0
> retw.n
> .literal .LC1, 1078523331
> test1:
> entry sp, 32
> call8 foo
> l32r a8, .LC1
> wfr f1, a10
> wfr f0, a8
> mul.s f0, f1, f0
> rfr a2, f0
> retw.n
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.cc (xtensa_register_move_cost):
> Add appropriate move costs between AR_REGS and FP_REGS.
> ---
> gcc/config/xtensa/xtensa.cc | 28 +++++++++++++++++++---------
> 1 file changed, 19 insertions(+), 9 deletions(-)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
That's a nice fix, thank you Suwa-san!
--
Thanks.
-- Max
