On Tue, 2025-01-21 at 22:14 +0800, Xi Ruoyao wrote:
> > > in GCC 13 the result is:
> > >
> > > or $r12,$r4,$r0
> >
> > Hmm, this strange move is caused by "&" in bstrpick_alsl_paired. Is it
> > really needed for the fusion?
>
> Never mind, it's needed or a = ((a & 0xffffffff) << 1) + a will blow up.
> Stupid I.
And my code is indeed broken due to the missing '&':
/* { dg-do run } */
/* { dg-options "-O2" } */
register long x asm ("s0");
#define TEST(x) (int)(((x & 0x114) << 3) + x)
[[gnu::noipa]] void
test (void)
{
x = TEST (x);
}
int
main (void)
{
x = 0xffff;
test ();
if (x != TEST (0xffff))
__builtin_trap ();
}
ends up:
0000000000000760 <test>:
760: 034452f7 andi $s0, $s0, 0x114
764: 00055ef7 alsl.w $s0, $s0, $s0, 0x3
768: 4c000020 ret
and fails. The fix would be like https://gcc.gnu.org/r15-5074.
> > > bstrpick.d $r4,$r12,31,0
> > > alsl.d $r4,$r4,$r6,2
> > > or $r12,$r5,$r0
> > > bstrpick.d $r5,$r12,31,0
> > > alsl.d $r5,$r5,$r6,2
> > > jr $r1
--
Xi Ruoyao <[email protected]>
School of Aerospace Science and Technology, Xidian University
