On Wed, Aug 20, 2025 at 4:30 AM Takayuki 'January June' Suwa
<jjsuwa_sys3...@yahoo.co.jp> wrote:
>
> This patch changes the implementation of the insn to test whether the
> result itself is negative or not, rather than the MSB of the result of
> the ABS machine instruction. This eliminates the need to consider bit-
> endianness and allows for longer branch distances.
>
> /* example */
> extern void foo(int);
> void test0(int a) {
> if (a == -2147483648)
> foo(a);
> }
> void test1(int a) {
> if (a != -2147483648)
> foo(a);
> }
>
> ;; before (endianness: little)
> test0:
> entry sp, 32
> abs a8, a2
> bbci a8, 31, .L1
> mov.n a10, a2
> call8 foo
> .L1:
> retw.n
> test1:
> entry sp, 32
> abs a8, a2
> bbsi a8, 31, .L4
> mov.n a10, a2
> call8 foo
> .L4:
> retw.n
>
> ;; after (endianness-independent)
> test0:
> entry sp, 32
> abs a8, a2
> bgez a8, .L1
> mov.n a10, a2
> call8 foo
> .L1:
> retw.n
> test1:
> entry sp, 32
> abs a8, a2
> bltz a8, .L4
> mov.n a10, a2
> call8 foo
> .L4:
> retw.n
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.md (*btrue_INT_MIN):
> Change the branch insn condition to test for a negative number
> rather than testing for the MSB.
> ---
> gcc/config/xtensa/xtensa.md | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
--
Thanks.
-- Max
