It seems that GCC and LLVM-Clang are using handwritten recursive descent parsers, and not machine generated, Bison-Flex based, bottom up parsing.
Could someone here please confirm that this is the case? And if so, why do mainstream compiler frameworks use handwritten parsers?
Update : interesting blog on this topic here
It seems that GCC and LLVM-Clang are using handwritten recursive descent parsers, and not machine generated, Bison-Flex based, bottom up parsing.
Bison in particular I don't think can handle the grammar without parsing some things ambiguously and doing a second pass later.
I know Haskell's Happy allows for monadic (i.e. state-dependent) parsers that can resolve the particular issue with C syntax, but I know of no C parser generators that allow a user-supplied state monad.
In theory, error recovery would be a point in favor of a handwritten parser, but my experience with GCC/Clang has been that the error messages are not particularly good.
As for performance - some of the claims seem unsubstantiated. Generating a big state machine using a parser generator should result in something that's O(n) and I doubt parsing is the bottleneck in much tooling.
