On Mon, Nov 18, 2013 at 10:08 AM, Richard Sandiford
<rdsandif...@googlemail.com> wrote:
> Jeff Law <l...@redhat.com> writes:
>> On 11/16/13 05:53, Richard Sandiford wrote:
>>> After the patch that went in yesterday, all calls to host_integerp and
>>> tree_low_cst pass a constant "pos" argument. This series replaces each
>>> function with two separate ones:
>> [ ... ]
>> So I've almost entirely ignored the whole wide-int conversion discussion
>> and I suspect I'm not entirely alone.
>>
>> Can you briefly summarize what's y'all are trying to accomplish with the
>> wide-int changes?
>
> At the moment, we can only handle tree and rtl integer constants that
> fit in 2 HOST_WIDE_INTs. The idea is to remove that limit. E.g. things
> like OImode (used in a few ports) will become a first-class citizen,
> with all OImode values being representable.
>
> Besides that headline reason, there are various side benefits. E.g.:
>
> - All INTEGER_CSTs can be viewed either in their TYPE_PRECISION or in
> "infinite" precision, which isn't possible for 128-bit constants today.
> (I.e. there's no way to distinguish signed and unsigned 128-bit constants
> in a double_int.)
>
> - Wider-than-2-HWI intermediate results can be represented as a single
> integer. I'm told this is useful for VRP. (wide-int is mostly Kenny
> and Mike's work, I've just been butting in recently.)
>
> - rtl-level constant folding can use the same code to handle all
> combinations of CONST_INT and CONST_DOUBLE (and CONST_WIDE_INT,
> on converted ports). At the moment we handle CONST_INT cases
> specially, and don't try as hard with CONST_DOUBLEs.
>
> Implementation-wise, it tries to make it so that the common single-HWI
> cases are still fast.
Sadly CONST_WIDE_INTs don't get a mode:
rtx
immed_wide_int_const (const wide_int &v, enum machine_mode mode)
{
...
/* It is so tempting to just put the mode in here. Must control
myself ... */
PUT_MODE (value, VOIDmode);
CWI_PUT_NUM_ELEM (value, len);
so much for an incentive to get more targets converted...
(only after all targets are converted we possibly can merge CONST_INT
and CONST_WIDE_INT).
Richard.
> Thanks,
> Richard
