https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114741
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Wilco from comment #2)
> It looks like the underlying bug is '^' being incorrectly treated like '?'
> in record_reg_classes (which is never used during reload). Fixing that
> results in the expected code being generated in all cases. It looks this
> issue was introduced in the original commit
> d1457701461d5a49ca6b5d8a6d1c83a37a6dc771
static const struct cpu_regmove_cost generic_armv9_a_regmove_cost =
{
1, /* GP2GP */
/* Spilling to int<->fp instead of memory is recommended so set
realistic costs compared to memmov_cost. */
3, /* GP2FP */
2, /* FP2GP */
2 /* FP2FP */
};
Note these costs are broken.
TARGET_REGISTER_MOVE_COST has this to say about the special value 2:
```
If reload sees an insn consisting of a single set between two hard registers,
and if TARGET_REGISTER_MOVE_COST applied to their classes returns a value of 2,
reload does not check to ensure that the constraints of the insn are met.
Setting a cost of other than 2 will allow reload to verify that the constraints
are met. You should do this if the ‘movm’ pattern’s constraints do not allow
such copying.
```
The way I implemented this for thunderx was have GP2GP being cost of 2 and then
be relative from there. That gave better code generation in general and even
less spilling. I know I wrote about this before too.
