[PATCH] D128297: [pseudo] Track heads as GSS nodes, rather than as "pending actions".

[Sam McCall via Phabricator via cfe-commits]

sammccall created this revision.
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IMO this model is simpler to understand (borrowed from the LR0 patch D127357 <https://reviews.llvm.org/D127357>).
It also makes error recovery easier to implement, as we have a simple list of
head nodes lying around to recover from when needed.
(It's not quite as nice as LR0 in this respect though).

It's slightly slower (2.24 -> 2.12 MB/S on my machine = 5%) but nothing close
to as bad as LR0.
However

- I think we'd have to eat a litle performance loss otherwise to implement error recovery.
- this frees up some complexity budget for optimizations like fastpath push/pop (this + fastpath is already faster than head)
- I haven't changed the data structure here and it's now pretty dumb, we can make it faster


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D128297

Files:
  clang-tools-extra/pseudo/include/clang-pseudo/GLR.h
  clang-tools-extra/pseudo/include/clang-pseudo/grammar/LRTable.h
  clang-tools-extra/pseudo/lib/GLR.cpp
  clang-tools-extra/pseudo/lib/grammar/LRTable.cpp
  clang-tools-extra/pseudo/unittests/GLRTest.cpp

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