|=?UTF-8?Q?Bison_determinis=E2=80=8Btic_LALR=281=29_parser_for_Java=2FC firstname.lastname@example.org (2012-08-17)|
|Re: Bison =?UTF-8?B?ZGV0ZXJtaW5pc+KAi3RpYyBMQUxSKDEpIHBhcnNlciBm?= =?U DrDiettrich1@aol.com (Hans-Peter Diettrich) (2012-08-18)|
|Re: Bison =?UTF-8?B?ZGV0ZXJtaW5pc+KAi3RpYyBMQUxSKDEpIHBhcnNlciBm?= =?U email@example.com (2012-08-20)|
|Re: Bison =?UTF-8?B?ZGV0ZXJtaW5pc+KAi3RpYyBMQUxSKDEpIHBhcnNlciBm?= =?U firstname.lastname@example.org (BGB) (2012-08-21)|
|=?UTF-8?Q?Re:_Bison_determinis=E2=80=8Btic_LALR=281=29?= =?UTF-8?Q?_pa email@example.com (BartC) (2012-08-22)|
|Re: Bison =?UTF-8?B?ZGV0ZXJtaW5pc+KAi3RpYyBMQUxSKDEpIHBhcnNlciBm?= =?U firstname.lastname@example.org (BGB) (2012-08-26)|
|Bison deterministic LALR parser for Java/C++ email@example.com (BartC) (2012-08-29)|
|speeding up C recompilation, was Re: Bison deterministic LALR firstname.lastname@example.org (BGB) (2012-09-04)|
|Re: C include handling, was Bison deterministic LALR email@example.com (Marco van de Voort) (2012-09-05)|
|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" <firstname.lastname@example.org> 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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