[llvm] [LV] Allow partial reductions with an extended bin op (PR #165536)

[Sam Tebbs via llvm-commits]

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@@ -1342,3 +1342,93 @@ exit:
   %red.next.lcssa = phi i64 [ %red.next, %loop ]
   ret i64 %red.next.lcssa
 }
+
+; A reduce.add(ext(mul(ext(A), ext(B)))) can't be turned into an
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SamTebbs33 wrote:

I'll clarify this by changing `A` to `This`.

https://github.com/llvm/llvm-project/pull/165536