[llvm] [AArch664] Replace uaddlv with addv for popcount operation (PR #121934)

[Cullen Rhodes via llvm-commits]

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@@ -243,6 +254,30 @@ define void @ctpop_i64() {
 }
 
 
+define i64 @popcnt(i64 %a, ptr %p) {
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c-rhodes wrote:

this seems equivalent to `@ctpop_i64` above, is that not sufficient? 

https://github.com/llvm/llvm-project/pull/121934