Nikita Popov 4ec4ac15ed [SCEVExpander] Fix addrec cost model (#106704) ...

The current isHighCostExpansion cost model for addrecs computes the cost
for some kind of polynomial expansion that does not appear to have any
relation to addrec expansion whatsoever.

A literal expansion of an affine addrec is a phi and add (plus the
expansion of start and step). For a non-affine addrec, we get another
phi+add for each additional addrec nested in the step recurrence.

This partially `fixes` https://github.com/llvm/llvm-project/issues/53205
(the runtime unroll test case in this PR).

2024-09-19 09:39:35 +02:00

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