Commit 998f3c5f authored by Committed by Xavier LeroyBrowse files
New parser based on new version of the Coq backend of Menhir (#276)
What's new: 1. A rewrite of the Coq interpreter of Menhir automaton, with dependent types removing the need for runtime checks for the well-formedness of the LR stack. This seem to cause some speedup on the parsing time (~10% for lexing + parsing). 2. Thanks to 1., it is now possible to avoid the use of int31 for comparing symbols: Since this is only used for validation, positives are enough. 3. Speedup of Validation: on my machine, the time needed for compiling Parser.v goes from about 2 minutes to about 1 minute. This seem to be related to a performance bug in the completeness validator and to the use of positive instead of int31. 3. Menhir now generates a dedicated inductive type for (semantic-value-carrying) tokens (in addition to the already existing inductive type for (non-semantic-value-carrying) terminals. The end result is that the OCaml support code for the parser no longer contain calls to Obj.magic. The bad side of this change is that the formal specification of the parser is perhaps harder to read. 4. The parser and its library are now free of axioms (I used to use axiom K and proof irrelevance for easing proofs involving dependent types). 5. Use of a dedicated custom negative coinductive type for the input stream of tokens, instead of Coq stdlib's `Stream`. `Stream` is a positive coinductive type, which are now deprecated by Coq. 6. The fuel of the parser is now specified using its logarithm instead of its actual value. This makes it possible to give large fuel values instead of using the `let rec fuel = S fuel` hack. 7. Some refactoring in the lexer, the parser and the Cabs syntax tree. The corresponding changes in Menhir have been released as part of version 20190626. The `MenhirLib` directory is identical to the content of the `src` directory of the corresponding `coq-menhirlib` opam package except that: - In order to try to make CompCert compatible with several Menhir versions without updates, we do not check the version of menhir is compatible with the version of coq-menhirlib. Hence the `Version.v` file is not present in CompCert's copy. - Build-system related files have been removed.