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

[Robert Lougher]

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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