[llvm] [SLP] Support ordered FAdd reductions in SLPVectorizer (PR #146570)

[Alexey Bataev via llvm-commits]

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@@ -22180,9 +22234,10 @@ class HorizontalReduction {
       // Add reduction values. The values are sorted for better vectorization
       // results.
       for (Value *V : PossibleRedVals) {
-        size_t Key, Idx;
-        std::tie(Key, Idx) = generateKeySubkey(V, &TLI, GenerateLoadsSubkey,
-                                               /*AllowAlternate=*/false);
+        size_t Key = 0, Idx = 0;
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alexey-bataev wrote:

I think better to separate it from the "associative" analysis and implement it in a separate function, in case if associative does not work. It will be much easier to read and maintain. Most of the logic for associative reductions can be dropped

https://github.com/llvm/llvm-project/pull/146570