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Re: [patch] Support vectorization of widening shifts
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.
> 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).
Thanks,
Ira
> That
> way you wouldn't need new tree codes and all architectures that can
> do widening conversions would benefit?
>
> Thanks,
> Richard.
>