[llvm] [GlobalISel] Combine into abd[su] and legalize abd[su] (PR #118865)

[Matt Arsenault via llvm-commits]

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In-Reply-To: <llvm.org/llvm/llvm-project/pull/118865 at github.com>


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@@ -93,9 +147,14 @@ define <8 x i16> @abdu_const_bothhigh() {
 }
 
 define <8 x i16> @abdu_undef(<8 x i16> %src1) {
-; CHECK-LABEL: abdu_undef:
-; CHECK:       // %bb.0:
-; CHECK-NEXT:    ret
+; CHECK-SD-LABEL: abdu_undef:
+; CHECK-SD:       // %bb.0:
+; CHECK-SD-NEXT:    ret
+;
+; CHECK-GI-LABEL: abdu_undef:
+; CHECK-GI:       // %bb.0:
+; CHECK-GI-NEXT:    uabd v0.8h, v0.8h, v0.8h
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arsenm wrote:

Undef can produce any register input, and will almost always end up using the first register in the allocation order

https://github.com/llvm/llvm-project/pull/118865