问题
I have a large c-code file (>9000 LoC) and attempt to parse it using this grammar:
https://github.com/antlr/grammars-v4/blob/master/c/C.g4
I waited for over an hour before aborting. The machine is a Core 2 Duo L9400 with 4GB of ram. Maximum java vm-heap-size is set to 2GB. It does not produce any parse errors, but it simply doesn't finish.
After doing some research, I set the prediction mode to SLL, which produces a "no viable alternative at input" within seconds.
Next, I set the prediction mode to LL_EXACT_AMBIG_DETECTION and attached a DiagnosticErrorListener to the parser. This produces a lot of "Ambiguity reports", mainly concerning declarations/declaration-specifiers. I assume this forces the parser to backtrack extremely often, which I is probably the explaination for the long parsing time?
Is there anything I can do to improve performance other than attempting to rewrite the grammar?
Any help is appreciated ;)
回答1:
First of all, it's important to note that ANTLR 4 never backtracks during parsing.
The grammar you are referring to is not SLL, which prevents you from using ANTLR 4 in its fastest mode. However, during or experiments we were able to identify a single rule which we altered to make the grammar SLL. You may be able to obtain the altered grammar via the antlr-interest mailing list. I'm at a concert now so I don't have access to it.
回答2:
Yep. we converted that from the spec with only a single rule change is a demonstration that you could do it. We will optimize that one soon.
来源：https://stackoverflow.com/questions/19311864/antlr-4-parsing-large-c-file-takes-forever