[llvm] [X86] getFauxShuffleMask - insert_subvector - skip undemanded subvectors (PR #129042)

[Simon Pilgrim via llvm-commits]

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@@ -3746,10 +3746,11 @@ define void @vec384_i16_widen_to_i48_factor3_broadcast_to_v8i48_factor8(ptr %in.
 ; AVX2-NEXT:    vmovdqa 48(%rdi), %xmm1
 ; AVX2-NEXT:    vpaddb 48(%rsi), %xmm1, %xmm1
 ; AVX2-NEXT:    vpaddb (%rsi), %xmm0, %xmm0
-; AVX2-NEXT:    vpbroadcastw %xmm0, %xmm0
+; AVX2-NEXT:    vpbroadcastw %xmm0, %ymm0
 ; AVX2-NEXT:    vpblendw {{.*#+}} xmm1 = xmm0[0],xmm1[1,2],xmm0[3],xmm1[4,5],xmm0[6],xmm1[7]
-; AVX2-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm1
-; AVX2-NEXT:    vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm1, %ymm1
+; AVX2-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; AVX2-NEXT:    vpblendw {{.*#+}} ymm2 = ymm2[0],ymm0[1],ymm2[2,3],ymm0[4],ymm2[5,6],ymm0[7],ymm2[8],ymm0[9],ymm2[10,11],ymm0[12],ymm2[13,14],ymm0[15]
+; AVX2-NEXT:    vpblendd {{.*#+}} ymm1 = ymm1[0,1,2,3],ymm2[4,5,6,7]
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RKSimon wrote:

This was reported back at #26392 - we've tried to resolve it repeatedly and never fixed it properly.

https://github.com/llvm/llvm-project/pull/129042