[llvm] [SLP]Analyze widened reduction leaves in the narrow type (PR #216062)

[Ryan Buchner via llvm-commits]

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@@ -336,6 +337,30 @@ bool isOnceUsedSeed(const Instruction *I);
 /// produce nan/inf.
 Instruction *lookThroughCastRoundTrip(Value *V, bool MustBeElidable);
 
+/// Narrow reduction leaf: the value, the shift applied after widening and
+/// the mask applied after the shift, clearing the bits the absorbed narrow
+/// shls shift out and applying the absorbed narrow and-masks. All-ones mask
+/// means nothing was absorbed and no and is needed.
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bababuck wrote:

Nit, had to do a double take reading it the first time:
```suggestion
/// shls shift out and applying the absorbed narrow and-masks. All-ones mask
/// means nothing was absorbed and no 'and' is needed.
```

https://github.com/llvm/llvm-project/pull/216062