[PATCH] D17201: [SCEV] Introduce a guarded backedge taken count and use it in LAA and LV

silviu.baranga@arm.com via llvm-commits llvm-commits at lists.llvm.org
Fri Mar 18 10:06:14 PDT 2016

sbaranga updated this revision to Diff 51037.
sbaranga added a comment.

Reworked the ExitNotTakenInfo allocation scheme to avoid allocating
un-needed SCEVUnionPredicates.

The new allocation scheme follows Sanjoy's idea:
we have a new optional structure that can hold optional (almost always not
needed) data. The optional data contains a SCEVPredicate and a vector
of ExitNotTakenInfo structs. The first elemet has the optional info if it
has a SCEVPredicate or there are more than one loop exits. The other
ExitNotTakenInfo structs will contain the extra info only if they have
a SCEVPredicate.

Note that we could pottentially modify this scheme such that the first
loop exit has a union of all the SCEV predicates (which doesn't have
the per-exit information, but uses less memory - in the cases where
we do need SCEV predicates).

Since the new structure is not trivial to traverse, we also have a new
iterator for this (which keeps the traversals simple to write).

Also followed up on the reset of the review comments from the last round.



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