Bison deterministic LALR parser for Java/C++

"BartC" <>
Wed, 29 Aug 2012 22:03:31 +0100

          From comp.compilers

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From: "BartC" <>
Newsgroups: comp.compilers
Date: Wed, 29 Aug 2012 22:03:31 +0100
Organization: A noiseless patient Spider
References: 12-08-005 12-08-006 12-08-009 12-08-014 12-08-015 12-08-018
Keywords: C, design, performance
Posted-Date: 29 Aug 2012 17:23:53 EDT

"BGB" <> wrote in message

> On 8/22/2012 8:04 AM, BartC wrote:

>> But even given all that, there are ways of dealing with huge header files so
>> that it is not necessary to repeatedly tokenise and parse the same headers
>> over and over again (for recompiling the same module, or compiling many
>> modules all sharing the same headers).
>> I've no idea whether many C compilers actually bother though; perhaps
>> it's easier to just recommend a faster computer..
> the problem here is that, although it isn't too hard to figure out
> possible optimizations, it is much harder to make them work in ways
> which don't violate the C standard.
> another issue is that things like precompiled headers are non-standard,
> and there is no real agreed-on convention for "hey, compiler, feel free
> to use precompiled headers here".

Why should how a compiler optimises its work violate the standard?
Provided the end results are the same, the compiler can do what it

However the C language and the way the C compilers are typically
invoked (for example just one-time to compile one module, so it's
forgotten it's compiled the same sets of headers a moment before)
doesn't make things easy. And it's possible that things such as
__TIME__ have been used in such a way that you are obliged to
recompile a header each time.

So it's easy to see why compilers may not bother!

Nevertheless, I think there is plenty that can be done, although I'm
not sure that creating intermediate files such as precompiled headers
is the way to go. It's better when a compiler is properly integrated
into an IDE, then the symbol tables built by a set of headers can be
made persistent much more easily.

Alternatively, it might be possible to just have a very faster parser!
And perhaps integrate the preprocessor so that it is not a separate
pass (I haven't attempted a C compiler so not sure if that's feasible;
my own source-level directives are handled by the lexer itself, or
sometimes by the parser).

>> [I've seen C compilers that keep preparsed versions of headers. Dunno
>> what they do with #if. Also see Microsoft's C# and other .NET languages,
>> that put all of the type info in the objects, so you can use the object
>> as a compiled include file. -John]
> AFAIK, the preparsed/precompiled headers for C generally handle #if and
> #ifdef and similar during the preprocessor as usual. this seems to be a
> large part of why there are many restrictions on the use of precompiled
> headers in those compilers which support them.
> AFAICT, languages like C# delay commands like #if or #ifdef until later
> (and impose restrictions on how they may be used). IIRC, they are
> generally handled at linking or at JIT.

With a new language then it's much easier to arrange matters so that
it's faster and simpler to compile. It might not even have conditional
directives, or any preprocessor at all; (C needs them because it is a
cruder, older language; I used to have conditional code, but no longer
and in any case it seemed an unsatisfactory approach).


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