[PATCH] D73741: [SCEV] SCEVExpander::isHighCostExpansionHelper(): cost-model polynomial recurrence

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

Hmm, though this is still a bit too pessimistic (high) cost if we the same operand (coeffient) more than once, consider:

  C0 + C1*x + C1*x*x

currently will be counted as `2x add + 3x mul`, but `C1*x` part can be reused,
so this is actually just `2x add + 2x mul`:

  C0 + C1*x*(1 + x)

I'm struggling to find a counter-example where such grouping would result in **too** optimistic (low) cost though.


Repository:
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https://reviews.llvm.org/D73741