[PATCH] D105390: [X86] Lower insertions into upper half of an 256-bit vector as broadcast+blend (PR50971)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/test/CodeGen/X86/avx512-insert-extract.ll:653
 define <16 x i16> @insert_v16i16(<16 x i16> %x, i16 %y, i16* %ptr) {
-; CHECK-LABEL: insert_v16i16:
-; CHECK:       ## %bb.0:
-; CHECK-NEXT:    vpinsrw $1, (%rsi), %xmm0, %xmm1
-; CHECK-NEXT:    vextracti128 $1, %ymm0, %xmm0
-; CHECK-NEXT:    vpinsrw $1, %edi, %xmm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
-; CHECK-NEXT:    retq
+; KNL-LABEL: insert_v16i16:
+; KNL:       ## %bb.0:
----------------
craig.topper wrote:
> Is this really better? I assume this what we get for an AVX2 target too. Not just KNL?
Multi-insert case does seem questionable, yes. We could improve this via:
```
define <16 x i16> @src(<16 x i16> %x, i16 %y, i16* %ptr) {
  %val = load i16, i16* %ptr
  %r1 = insertelement <16 x i16> %x, i16 %val, i32 1
  %r2 = insertelement <16 x i16> %r1, i16 %y, i32 9
  ret <16 x i16> %r2
}
define <16 x i16> @tgt(<16 x i16> %x, i16 %y, i16* %ptr) {
  %val = load i16, i16* %ptr
  %r1 = insertelement <16 x i16> undef, i16 %val, i32 1
  %r2 = insertelement <16 x i16> %r1, i16 %y, i32 9
  %r3 = select <16 x i1> <i1 1, i1 0, i1 1, i1 1, i1 1, i1 1, i1 1, i1 1, i1 1, i1 0, i1 1, i1 1, i1 1, i1 1, i1 1, i1 1>, <16 x i16> %x, <16 x i16> %r2
  ret <16 x i16> %r3
}
```
then we get
```
        .text
        .file   "test.ll"
        .globl  src                             # -- Begin function src
        .p2align        4, 0x90
        .type   src, at function
src:                                    # @src
        .cfi_startproc
# %bb.0:
        vpbroadcastw    (%rsi), %xmm1
        vpblendw        $2, %xmm1, %xmm0, %xmm1         # xmm1 = xmm0[0],xmm1[1],xmm0[2,3,4,5,6,7]
        vmovd   %edi, %xmm2
        vpbroadcastw    %xmm2, %ymm2
        vpblendw        $2, %ymm2, %ymm0, %ymm0         # ymm0 = ymm0[0],ymm2[1],ymm0[2,3,4,5,6,7,8],ymm2[9],ymm0[10,11,12,13,14,15]
        vpblendd        $240, %ymm0, %ymm1, %ymm0       # ymm0 = ymm1[0,1,2,3],ymm0[4,5,6,7]
        retq
.Lfunc_end0:
        .size   src, .Lfunc_end0-src
        .cfi_endproc
                                        # -- End function
        .globl  tgt                             # -- Begin function tgt
        .p2align        4, 0x90
        .type   tgt, at function
tgt:                                    # @tgt
        .cfi_startproc
# %bb.0:
        vpbroadcastw    (%rsi), %xmm1
        vmovd   %edi, %xmm2
        vpslld  $16, %xmm2, %xmm2
        vinserti128     $1, %xmm2, %ymm1, %ymm1
        vpblendw        $2, %ymm1, %ymm0, %ymm0         # ymm0 = ymm0[0],ymm1[1],ymm0[2,3,4,5,6,7,8],ymm1[9],ymm0[10,11,12,13,14,15]
        retq
.Lfunc_end1:
        .size   tgt, .Lfunc_end1-tgt
        .cfi_endproc
                                        # -- End function
        .section        ".note.GNU-stack","", at progbits
```


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