On 09/26/14 09:31, Ilya Tocar wrote:
It's not a question of performance, but of design.
Obviously, but I still fail to see why honoring HARD_REGNO_MODE_OK is
bad design. I suspect that even without avx512 changes not honoring it will
bite us sooner or later.
If we look at maybe_mode_change:
/* Register REGNO was originally set in ORIG_MODE. It - or a copy of it -
was copied in COPY_MODE to COPY_REGNO, and then COPY_REGNO was accessed
in NEW_MODE.
Return a NEW_MODE rtx for REGNO if that's OK, otherwise return
NULL_RTX. */
static rtx
maybe_mode_change (enum machine_mode orig_mode, enum machine_mode copy_mode,
enum machine_mode new_mode, unsigned int regno,
unsigned int copy_regno ATTRIBUTE_UNUSED)
{
if (GET_MODE_SIZE (copy_mode) < GET_MODE_SIZE (orig_mode)
&& GET_MODE_SIZE (copy_mode) < GET_MODE_SIZE (new_mode))
return NULL_RTX;
if (orig_mode == new_mode)
return gen_rtx_raw_REG (new_mode, regno);
REGNO was originally set in ORIG_MODE, that's an invariant of this
fucntion. ORIG_MODE == NEW_MODE in the conditional which generates the
new reg. How in the world can HARD_REGNO_MODE_OK be false in that case?
If it was false in that case, then how in the world did a value get put
in REGNO using ORIG_MODE/NEW_MODE to start with?!?
It really looks like you're papering over a problem.
Jeff
