[PATCH] Teach the DAGCombiner how to fold concat_vector nodes when the input is two BUILD_VECTOR nodes.

[Robert Lougher]

Hi Bill,

Thanks again for the review.  I now have commit access, and have
commited it at r201158.

Thanks,
Rob.


On 6 February 2014 14:24, Robert Lougher <rob.lougher at gmail.com> wrote:
> Hi Bill,
>
> Thanks for the review!  Could you please commit it for me, as I don't
> have commit access.
>
> Thanks,
> Rob.
>
>
> On 6 February 2014 08:53, Bill Wendling <isanbard at gmail.com> wrote:
>> This LGTM.
>>
>> -bw
>>
>> On Feb 4, 2014, at 11:48 AM, Robert Lougher <rob.lougher at gmail.com> wrote:
>>
>>> ping.
>>>
>>> On 28 January 2014 17:40, Robert Lougher <rob.lougher at gmail.com> wrote:
>>>> Hi,
>>>>
>>>> This patch teaches the DAGCombiner how to fold concat_vector nodes
>>>> when the input is two BUILD_VECTOR nodes, e.g.:
>>>>
>>>> (concat_vectors (BUILD_VECTOR a1, a2, a3, a4), (BUILD_VECTOR b1, b2, b3, b4))
>>>> ->
>>>> (BUILD_VECTOR a1, a2, a3, a4, b1, b2, b3, b4)
>>>>
>>>> This can be seen with the following IR:
>>>>
>>>> define <8 x float> @memory4(float* %p) {
>>>>  %1 = load float* %p, align 4
>>>>  %2 = insertelement <4 x float> undef, float %1, i32 0
>>>>  %3 = insertelement <4 x float> %2, float %1, i32 1
>>>>  %4 = insertelement <4 x float> %3, float %1, i32 2
>>>>  %5 = insertelement <4 x float> %4, float %1, i32 3
>>>>  %6 = shufflevector <4 x float> %5, <4 x float> undef, <8 x i32> <i32
>>>> 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
>>>>
>>>> The shufflevector is turned into a concat_vectors node, and the
>>>> insertelements into a BUILD_VECTOR.
>>>>
>>>> On AVX, without the patch this generates two instructions:
>>>>
>>>> vbroadcastss (%rdi), %xmm0
>>>> vinsertf128 $1, %xmm0, %ymm0, %ymm0
>>>>
>>>> With the patch:
>>>>
>>>> vbroadcastss (%rdi), %ymm0
>>>>
>>>> This is because the whole sequence was not recognized as a 256-bit
>>>> vbroadcast by LowerVectorBroadcast (X86ISelLowering.cpp) due to the
>>>> concat_vectors.
>>>>
>>>> I have added tests to avx-vbroadcast.ll and avx2-vbroadcast.ll that
>>>> check both single and double vbroadcasts.  If the patch looks OK
>>>> please submit for me.
>>>>
>>>> Thanks,
>>>> Rob.
>>>>
>>>> --
>>>> Robert Lougher
>>>> SN Systems - Sony Computer Entertainment Group
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