[AVX512] Bring back vector-shuffle lowering support through broadcasts

[Robert Khasanov]

lower512BitVectorShuffle is already existed in X86ISelLowering.cpp. There
is switch inside the function.
Vector-shuffle can be lowered also to UNPACK{H,L}, PSHUF, VPERM, VPERMILP.
For these instructions lowering codes are not similar.

2014-10-22 15:13 GMT+04:00 Demikhovsky, Elena <elena.demikhovsky at intel.com>:

>  But why it can’t be one lower512VectorShuffle at least?
>
>
>
> -          * Elena*
>
>
>
> *From:* Robert Khasanov [mailto:rob.khasanov at gmail.com]
> *Sent:* Wednesday, October 22, 2014 14:11
> *To:* Demikhovsky, Elena
> *Cc:* reviews+D5885+public+df9a14ab3195f7ff at reviews.llvm.org;
> chandlerc at gmail.com; llvm-commits at cs.uiuc.edu
> *Subject:* Re: [AVX512] Bring back vector-shuffle lowering support
> through broadcasts
>
>
>
> Elena,
>
>
>
> On 256-bit versions of vector-shuffle lowering (lowerV8F32VectorShuffle,
> lowerV8I32VectorShuffle etc), you can see that there is big difference
> inside the functions (except broadcasts and blends). I assume Chandler
> provided opportunity to implement 512-bit vector-shuffle lowering in the
> same way in future.
>
>
>
> 2014-10-22 12:08 GMT+04:00 Demikhovsky, Elena <elena.demikhovsky at intel.com
> >:
>
> Why do you need so many functions:
> lowerV16F32VectorShuffle
> lowerV8I64VectorShuffle
> lowerV16I32VectorShuffle
> .. ?
>
> I don't see a big diff between them.
>
> -  Elena
>
>
>
> -----Original Message-----
> From: Robert Khasanov [mailto:rob.khasanov at gmail.com]
> Sent: Tuesday, October 21, 2014 21:03
> To: rob.khasanov at gmail.com; chandlerc at gmail.com
> Cc: Demikhovsky, Elena; anemet at apple.com; llvm-commits at cs.uiuc.edu
> Subject: [PATCH] [AVX512] Bring back vector-shuffle lowering support
> through broadcasts
>
> Hi chandlerc,
>
> I found that after your commit at rev219046 512-bit broadcasts lowering
> become non-optimal. Most of tests on broadcasting and embedded broadcasting
> were changed and they doesn’t produce efficient code.
>
> Example below is from your commit changes (it’s the first test from
> test/CodeGen/X86/avx512-vbroadcast.ll):
>
>  define   <16 x i32> @_inreg16xi32(i32 %a) {
>  ; CHECK-LABEL: _inreg16xi32:
>  ; CHECK:       ## BB#0:
> -; CHECK-NEXT:    vpbroadcastd %edi, %zmm0
> +; CHECK-NEXT:    vmovd %edi, %xmm0
> +; CHECK-NEXT:    vpbroadcastd %xmm0, %ymm0
> +; CHECK-NEXT:    vinserti64x4 $1, %ymm0, %zmm0, %zmm0
>  ; CHECK-NEXT:    retq
>  %b = insertelement <16 x i32> undef, i32 %a, i32 0
>   %c = shufflevector <16 x i32> %b, <16 x i32> undef, <16 x i32>
> zeroinitializer
>    ret <16 x i32> %c
> }
>
> Here, 256-bit broadcast was generated instead of 512-bit one.
>
> I investigated the reason, found that in your version of vector-shuffle
> lowering there is no AVX-512 support.
>
> In this patch
> 1) I added vector-shuffle lowering through broadcasts
> 2) Removed asserts and branches likes because this is incorrect
> -  assert(Subtarget->hasDQI() && "We can only lower v8i64 with
> AVX-512-DQI");
> 3) Fixed lowering tests
>
> http://reviews.llvm.org/D5885
>
> Files:
>   lib/Target/X86/X86ISelLowering.cpp
>   lib/Target/X86/X86InstrAVX512.td
>   test/CodeGen/X86/avx512-arith.ll
>   test/CodeGen/X86/avx512-vbroadcast.ll
>   test/CodeGen/X86/avx512-vec-cmp.ll
>   test/CodeGen/X86/vector-shuffle-512-v8.ll
>
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