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Re: Using gen_int_mode instead of GEN_INT minot testsuite fallout on MIPS


On Fri, Sep 13, 2013 at 10:33 AM, Richard Sandiford
<rdsandiford@googlemail.com> wrote:
> Richard Biener <richard.guenther@gmail.com> writes:
>>> Yeah.  I don't think it makes sense to canonise PSI to 32 bits when we
>>> know it has fewer than 32 bits.  It's still going to be wrong, and will
>>> still defeat one of the main purposes of canonical constants, which is
>>> to make equality obvious.  E.g. we'd still treat PSI constants
>>>
>>>   (const_int 0x...ff80000000)
>>>
>>> and
>>>
>>>   (const_int 0x...ffc0000000)
>>>
>>> as different, even though they're both zero for a 24-bit PSI.
>>>
>>> This partial integer mode stuff is just a big hack.  Like you say,
>>> we can only really do something sensible if we know what the real
>>> precision is.
>>>
>>> So I'd rather leave things as they are for this series.  The precision
>>> effectively becomes 65535 thanks to the underlying unsigned short array,
>>> so like you say, trunc_int_for_mode is a no-op for partial modes.
>>> Changing GEN_INT to gen_int_mode shouldn't make any difference.
>>>
>>> What do you think about the patch for CC modes?
>>
>> I wonder if we can do without changing gen_int_mode by fixing the callers
>> like you did for cse.c (that patch is ok).
>
> But the point of the gen_int_mode patch is that (for better or worse)
> CONST_INT is the right choice of rtx for constant CC values.  I'd like
> eventually to get rid of all GEN_INT callers, and some of those callers
> will sometimes or always be handling CC modes.  This would then crop up
> again in a legitimate context.
>
> IMO, cse.c was buggy not because it was trying to generate a CCmode
> CONST_INT, but because anchor optimisations involve addition, which
> isn't defined for CC modes.
>
> I think gen_int_mode should do the right thing for all CONST_INT modes.
> gen_int_mode (X, MODE) should really be the moral equivalent of
> gen_rtx_CONST_INT (MODE, X), despite the confusingly-swapped parameters.

Yeah, ok.  But the GEN_INT changes have already uncovered quite some bugs
so maybe let us discover a few more CCmode bugs first? ...

Anyway, as you choose - the patch is ok in the end.

Thanks,
Richard.

> Thanks,
> Richard


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