[PATCH] D87045: [LoopNest] Handle loop-nest passes in LoopPassManager

[Ta-Wei Tu via Phabricator via llvm-commits]

TaWeiTu added a comment.

In D87045#2301614 <https://reviews.llvm.org/D87045#2301614>, @ychen wrote:

> From http://llvm.org/OpenProjects.html#llvm_loopnest, it was mentioned that
> "If you decide to write it as a loop pass, then you are wasting compile time to traverse to your pass and return right away when the given loop is not the outermost loop."
>
> Taking another look at the overall approach of this patch: currently for all loops (top-level or nested) in a function, when encountering a loop nest pass in LPM, a LoopNest is calculated and the loop nest pass is called with the computed LoopNest. Does this help compile-time in practice? It feels like it is essentially a loop pass that got passed a LoopNest as an incoming parameter that could be equally implemented (without this patch) with a normal loop pass that computes LoopNest by itself? This seems does not solve the problem quoted  above.
>
> To achieve that, I think we need to change FunctionToLoopPassAdaptor to dispatch top-level loops (aside from to regular loops and LPMs) to a LoopNestPassManager managing only loop nest passes or a loop nest pass directly.

If I understood correctly, I think the follow-up patch D87531 <https://reviews.llvm.org/D87531> is designed to address the issue.
Specifically, in `FunctionToLoopPassAdaptor`, if the input pass is a loop pass or an LPM containing both loop passes and loop-nest passes, all loops in the function have to be processed regardless if they're top-level or not.
On the other hand, if the input pass is a loop-nest pass or is an LPM containing only loop-nest passes, only top-level loops are sent to the worklist and processed.

Does this solve the problem you mentioned? Thanks!


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