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Re: [PATCH] Allow fwprop to undo vectorization harm (PR68961)


On Wed, Jul 6, 2016 at 3:18 PM, Richard Biener <rguenther@suse.de> wrote:

>> > 2016-07-04  Richard Biener  <rguenther@suse.de>
>> >
>> >     PR rtl-optimization/68961
>> >     * fwprop.c (propagate_rtx): Allow SUBREGs of VEC_CONCAT and CONCAT
>> >     to simplify to a non-constant.
>> >
>> >     * gcc.target/i386/pr68961.c: New testcase.
>>
>> Thanks, LGTM.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, it causes
>
> FAIL: gcc.target/i386/sse2-load-multi.c scan-assembler-times movup 2
>
> as the peephole created for that testcase no longer applies as fwprop
> does
>
> In insn 10, replacing
>  (vec_concat:V2DF (vec_select:DF (reg:V2DF 91)
>             (parallel [
>                     (const_int 0 [0])
>                 ]))
>         (mem:DF (reg/f:DI 95) [0  S8 A128]))
>  with (vec_concat:V2DF (reg:DF 93 [ MEM[(const double *)&a + 8B] ])
>         (mem:DF (reg/f:DI 95) [0  S8 A128]))
> Changed insn 10
>
> resulting in
>
>         movsd   a+8(%rip), %xmm0
>         movhpd  a+16(%rip), %xmm0
>
> again rather than movupd.
>
> Uros, there is probably a missing peephole for the new form - can you
> fix this as a followup or should I hold on this patch for a bit longer?

No, please proceed with the patch, I'll fix this fallout with a
followup patch in a couple of days.

Uros.


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