[llvm-dev] [GlobalISel] Prioritizing long patterns in combiner over short ones

[Jason Eckhardt via llvm-dev]

GICombineGroup may be of use:

// A group of combine rules that can be added to a GICombiner or another group.
class GICombineGroup<list<GICombine> rules> : GICombine {
  // The rules contained in this group. The rules in a group are flattened into
  // a single list and sorted into whatever order is most efficient. However,
  // they will never be re-ordered such that behaviour differs from the
  // specified order. It is therefore possible to use the order of rules in this
  // list to describe priorities.
  let Rules = rules;
}


________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Dominik Montada via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Tuesday, December 15, 2020 9:09 AM
To: LLVM Developers' List <llvm-dev at lists.llvm.org>
Subject: [llvm-dev] [GlobalISel] Prioritizing long patterns in combiner over short ones

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Hi,

I'm currently writing target specific combiners with GlobalISel. I have
a case where a sub-node of a larger pattern also matches another,
smaller combiner pattern. Because the combiner runs top-down, the
smaller pattern is matched before the larger pattern has a chance to be
matched. Do I have to teach my larger pattern to handle this case or is
there a better way to do this?

More importantly, are there any plans to improve this behavior?

Cheers,

Dominik

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