[llvm] [InstCombine] Do not request non-splat vector support in code reviews (NFC) (PR #90709)

[via llvm-commits]

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@@ -554,3 +554,11 @@ guidelines.
    use of ValueTracking queries. Whether this makes sense depends on the case,
    but it's usually a good idea to only handle the constant pattern first, and
    then generalize later if it seems useful.
+
+## Guidelines for reviewers
+
+ * Do not ask contributors to implement non-splat vector support in code
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goldsteinn wrote:

Hopefully #85676 will change that :)

https://github.com/llvm/llvm-project/pull/90709