Restructure ACTION and GOTO tables. #194
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With this change, the `Parser.action` and `.goto` tables are now 2-layer hash tables, using states as the keys for the outer tables and symbols as the keys for the inner tables. Functionally, this means that `action[state, symbol]` becomes `action[state][symbol]`, and likewise for `goto`. This also allows the `expected` table to be eliminated, as it can be quickly computed from `action[state]` when needed.
EricRahm
approved these changes
Sep 30, 2024
compiler/front_end/lr1.py
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| if new_action: | ||
| if (i, terminal) in action and action[i, terminal] != new_action: | ||
| action.setdefault(i, {}) |
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Maybe using defaultdict throughout would be a little simpler. In this case it seems like action could just be a fixed size list of len(item_sets). It kind of depends if we expected an entry for every value of i or if it's sparsely populated. Either way this could be a further improvement, this looks good as-is.
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Done. I'm not sure why I didn't do that in the first place.
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With this change, the
Parser.actionand.gototables are now 2-layer hash tables, using states as the keys for the outer tables and symbols as the keys for the inner tables. Functionally, this means thataction[state, symbol]becomesaction[state][symbol], and likewise forgoto.This also allows the
expectedtable to be eliminated, as it can be quickly computed fromaction[state]when needed.This goal of this change is to have a more compact representation for issue #193: by structuring the tables this way, state numbers do not need to be repeated in the serialized output. Eliminating
expectedalso provides a modest savings. The total savings is approximately 55%, going from 4.3MB without this change to 1.9MB with this change.