Re: [patch] Support vectorization of widening shifts

[Richard Guenther <richard dot guenther at gmail dot com>]

On Tue, Sep 27, 2011 at 8:32 AM, Ira Rosen <ira.rosen@linaro.org> wrote:
> On 26 September 2011 17:12, Richard Guenther <richard.guenther@gmail.com> wrote:
>> On Mon, Sep 19, 2011 at 9:54 AM, Ira Rosen <ira.rosen@linaro.org> wrote:
>>> Hi,
>>>
>>> This patch adds a support of widening shift left. The following
>>> pattern is detected:
>>>
>>> type a_t;
>>> TYPE a_T, res_T;
>>>
>>> a_t = ;
>>> a_T = (TYPE) a_t;
>>> res_T = a_T << CONST;
>>>
>>> ('TYPE' is at least 2 times bigger than 'type', and CONST is at most
>>> the size of 'type')
>>>
>>> and create a pattern stmt using new tree code WIDEN_SHIFT_LEFT_EXPR for it:
>>>
>>> a_t = ;
>>> a_T = (TYPE) a_t;
>>> res_T = a_T << CONST;
>>> ? ?--> ?res_T = a_t w<< CONST;
>>>
>>> which is later transformed into:
>>>
>>> va_t = ;
>>> vres_T0 = WIDEN_SHIFT_LEFT_LO_EXPR <va_t, CONST>;
>>> vres_T1 = WIDEN_SHIFT_LEFT_HI_EXPR <va_t, CONST>;
>>>
>>> This patch also supports unsigned types, and cases when 'TYPE' is 4
>>> times bigger than 'type'.
>>> This feature is similar to vectorization of widening multiplication.
>>>
>>> Bootstrapped on powerpc64-suse-linux, tested on powerpc64-suse-linux
>>> and arm-linux-gnueabi
>>> OK for mainline?
>>
>> Hmm, it doesn't look like arm has real widening shift instructions.
>
> It does: vshll. The implementation may look awkward because we don't
> support multiple vector sizes in the same operation (vshll takes a
> 64-bit vector and produces a 128-bit vector), but the resulting code
> is just the instruction itself.

Ah, ok.  Can you please do s/SHIFT_LEFT/LSHIFT/ on the new tree
code names for consistency with LSHIFT_EXPR?  Also please implement
some gimple verification for the new codes instead of sticking them
to the /* FIXME */ case in tree-cfg.c.

>> So why not split this into the widening, shift parts in the vectorizer?
>
> What do you mean? (We of course already support widening first and
> then shifting the widened value).

Of course.

Ok with the above changes.

Thanks,
Richard.

> Thanks,
> Ira
>
>> That
>> way you wouldn't need new tree codes and all architectures that can
>> do widening conversions would benefit?
>>
>> Thanks,
>> Richard.
>>
>