[llvm] [SDAG] Promote extract subvector in more cases without falling back to build vectors. (PR #212156)

[Matt Arsenault via llvm-commits]

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@@ -49,10 +57,11 @@ define <2 x i8> @test_v16i8_v2i32_016(<16 x i8> %a, <16 x i8> %b) {
 define <2 x i8> @test_v8i8_v2i32_08(<8 x i8> %a, <8 x i8> %b) {
 ; CHECK-SD-LABEL: test_v8i8_v2i32_08:
 ; CHECK-SD:       // %bb.0:
-; CHECK-SD-NEXT:    // kill: def $d0 killed $d0 def $q0
-; CHECK-SD-NEXT:    // kill: def $d1 killed $d1 def $q1
-; CHECK-SD-NEXT:    mov b0, v0.b[0]
-; CHECK-SD-NEXT:    mov v0.b[4], v1.b[0]
+; CHECK-SD-NEXT:    zip1 v1.8b, v1.8b, v1.8b
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arsenm wrote:

Regressions 

https://github.com/llvm/llvm-project/pull/212156