On Sat, Jun 7, 2025 at 10:05 PM Takayuki 'January June' Suwa
<jjsuwa_sys3...@yahoo.co.jp> wrote:
>
> By using the previously unused CEIL|FLOOR.S floating-point coprocessor
> instructions. In addition, two instruction operand format codes are added
> to output the scale value as assembler source.
>
> /* example */
> int test0(float a) {
> return __builtin_lceilf(a);
> }
> int test1(float a) {
> return __builtin_lceilf(a * 2);
> }
> int test2(float a) {
> return __builtin_lfloorf(a);
> }
> int test3(float a) {
> return __builtin_lfloorf(a * 32768);
> }
>
> ;; result
> test0:
> entry sp, 32
> wfr f0, a2
> ceil.s a2, f0, 0
> retw.n
> test1:
> entry sp, 32
> wfr f0, a2
> ceil.s a2, f0, 1
> retw.n
> test2:
> entry sp, 32
> wfr f0, a2
> floor.s a2, f0, 0
> retw.n
> test3:
> entry sp, 32
> wfr f0, a2
> floor.s a2, f0, 15
> retw.n
>
> However, because the rounding-half behavior (e.g., the rule that determines
> whether 1.5 should be rounded to 1 or 2) of the two is inconsistent;
> the lroundsfsi2 pattern is explicitly specified that rounding to nearest
> integer and away from zero, but the other hand, the ROUND.S instruction is
> not specified that by the ISA and is implementation-dependent.
>
> Therefore lroundsfsi2 cannot be implemented by ROUND.S.
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.cc (printx, print_operand):
> Add two instruction operand format codes 'U' and 'V',
> whose represent scale factors of 0 to 15th positive/negative
> power of two.
> * gcc/config/xtensa/xtensa.md (c_enum "unspec"):
> Add UNSPEC_CEIL and UNSPEC_FLOOR.
> (int_iterator ANY_ROUND, int_attr m_round):
> New integer iterator and its attribute.
> (fix<s_fix>_truncsfsi2, *fix<s_fix>_truncsfsi2_2x,
> *fix<s_fix>_truncsfsi2_scaled, float<s_float>sisf2,
> *float<s_float>sisf2_scaled):
> Use output templates with the operand formats added above,
> instead of individual output statements.
> (l<m_round>sfsi2, *l<m_round>sfsi2_2x, *l<m_round>sfsi2_scaled):
> New insn patterns.
> ---
> gcc/config/xtensa/xtensa.cc | 16 ++++++++++++
> gcc/config/xtensa/xtensa.md | 50 ++++++++++++++++++++++++++++---------
> 2 files changed, 54 insertions(+), 12 deletions(-)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
--
Thanks.
-- Max
