[llvm] Reland "RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG" (PR #168353)

[Sergei Barannikov via llvm-commits]

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@@ -1727,7 +1727,7 @@ define <16 x i8> @test_concat_v16i8_v8i8_v16i8(<8 x i8> %x, <16 x i8> %y) #0 {
 ; CHECK-GI-LABEL: test_concat_v16i8_v8i8_v16i8:
 ; CHECK-GI:       // %bb.0: // %entry
 ; CHECK-GI-NEXT:    mov v2.16b, v1.16b
-; CHECK-GI-NEXT:    // kill: def $d0 killed $d0 def $q0
+; CHECK-GI-NEXT:    // kill: def $d0 killed $d0 def $q0 def $q0 def $q0 def $q0 def $q0 def $q0 def $q0 def $q0
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s-barannikov wrote:

Can `addRegisterDefined()` help with these multiple identical defs?

https://github.com/llvm/llvm-project/pull/168353