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

[Demikhovsky, Elena]

Just use one function and pass the VT as parameter or do everything inside the caller.
I don’t see the reason for writing 4 similar functions.

-           Elena

From: Robert Khasanov [mailto:rob.khasanov at gmail.com]
Sent: Wednesday, October 22, 2014 14:27
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

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<mailto: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<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<mailto:reviews%2BD5885%2Bpublic%2Bdf9a14ab3195f7ff at reviews.llvm.org>; chandlerc at gmail.com<mailto:chandlerc at gmail.com>; llvm-commits at cs.uiuc.edu<mailto: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<mailto: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<mailto:rob.khasanov at gmail.com>]
Sent: Tuesday, October 21, 2014 21:03
To: rob.khasanov at gmail.com<mailto:rob.khasanov at gmail.com>; chandlerc at gmail.com<mailto:chandlerc at gmail.com>
Cc: Demikhovsky, Elena; anemet at apple.com<mailto:anemet at apple.com>; llvm-commits at cs.uiuc.edu<mailto: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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