On Fri, Sep 10, 2021 at 03:58:47PM +0200, Richard Biener wrote:
> On September 10, 2021 3:30:10 PM GMT+02:00, Segher Boessenkool
> <seg...@kernel.crashing.org> wrote:
> >TRULY_NOOP_TRUNCATION does not make sense to ask if changing mode class.
>
> OK, so there's a mode class comparison missing here which should be a better
> fix than calling validate_subreg?
Yes, we should not call TRULY_NOOP_TRUNCATION_MODES_P for any random two
modes: such a truncation needs to have a meaning at all, for the
question to make any sense. Maybe we can add an assert to this macro to
root out nonsensical callers?
Btw. We have
#define TRULY_NOOP_TRUNCATION_MODES_P(MODE1, MODE2) \
(targetm.truly_noop_truncation (GET_MODE_PRECISION (MODE1), \
GET_MODE_PRECISION (MODE2)))
which is not optimal, either: does truncating DFmode to HFmode behave
the same as truncating DImode to HImode, on every target? On *any*
target, even?!
Segher
