[llvm] [X86] combineINSERT_SUBVECTOR - fold insert_subvector(base,extract_subvector(broadcast)) -> blend shuffle(base,broadcast) (PR #133083)

[Phoebe Wang via llvm-commits]

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@@ -2837,8 +2837,7 @@ define void @vec384_i8_widen_to_i48_factor6_broadcast_to_v8i48_factor8(ptr %in.v
 ; AVX512F-NEXT:    vpalignr {{.*#+}} xmm1 = xmm1[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15],xmm0[0]
 ; AVX512F-NEXT:    vpshufb {{.*#+}} xmm1 = xmm1[15,0,1,2,3,4,15,6,7,8,9,10,15,12,13,14]
 ; AVX512F-NEXT:    vpbroadcastb %xmm0, %ymm0
-; AVX512F-NEXT:    vinserti64x4 $1, %ymm0, %zmm0, %zmm0
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phoebewang wrote:

Why did we insert the value we never used?

https://github.com/llvm/llvm-project/pull/133083