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Re: [66/77] Use scalar_mode for constant integers


Jeff Law <law@redhat.com> writes:
> On 07/13/2017 03:02 AM, Richard Sandiford wrote:
>> This patch treats the mode associated with an integer constant as a
>> scalar_mode.  We can't use the more natural-sounding scalar_int_mode
>> because we also use (const_int 0) for bounds-checking modes.  (It might
>> be worth adding a bounds-specific code instead, but that's for another
>> day.)
> Is that the only reason why we can't use scalar_int_mode here -- the
> bounds checking stuff?  What if it were to just magically disappear?

:-)  I *think* that was the only case, but it's possible that once
we hit it, we didn't look much further.  

[...]

>> We didn't try to make these functions take scalar_mode arguments
>> because in many cases that would be too invasive at this stage.
>> Maybe it would become feasible in future.  Also, the long-term
>> direction should probably be to add modes to constant integers
>> rather than have then as VOIDmode odd-ones-out.  That would remove
>> the need for rtx_mode_t and thus remove the question whether they
>> should use scalar_int_mode, scalar_mode or machine_mode.
> THe lack of a mode on CONST_INTs is a long standing wart.  It's been
> eons since we really thought about how to fix it.    I'd have to dig
> real deep to remember why we've let the wart stand so long

When I last looked at the history, I got the impression it was just
lack of time.  I have a vague plan for how we could transition to
integers with modes, but then I've had the same plan for a while now
and no realistic chance of getting time to do it.

Thanks,
Richard


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