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Groups > comp.lang.c > #61481

Re: Understandability

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c
Subject Re: Understandability
Date 2015-05-04 09:15 +0200
Organization A noiseless patient Spider
Message-ID <mi769d$ip9$1@dont-email.me> (permalink)
References <f088f6c5-01bd-44ca-b51a-04e71d1bd169@googlegroups.com> <WWW-20150502040535@ram.dialup.fu-berlin.de> <mi2fei$75j$2@dont-email.me> <ddd5d238-7d70-4b42-a6f9-c449ea163c27@googlegroups.com>

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On 02/05/15 18:13, David Kleinecke wrote:
> On Saturday, May 2, 2015 at 5:21:48 AM UTC-7, Noob wrote:
>> On 02/05/2015 04:05, Stefan Ram wrote:
>>
>>> Then restrict your search to wikipedia.
>>
>> Indeed!
>>
>> https://en.wikipedia.org/wiki/GNU_Compiler_Collection
>>
>>> The GNU Compiler Collection (GCC) is a compiler system produced by
>>> the GNU Project supporting various programming languages. GCC is a
>>> key component of the GNU toolchain.
>>
>> https://en.wikipedia.org/wiki/Compiler
>>
>>> A compiler is a computer program (or set of programs) that transforms
>>> source code written in a programming language (the source language)
>>> into another computer language (the target language, often having a
>>> binary form known as object code). The most common reason for
>>> converting a source code is to create an executable program.
>>
>> Regards.
> 
> The Wikipedia page on "GNU Compiler Collection" is very poorly written
> and is an excellent example of what I deplore.

Feel free to read it anyway - it's better than guessing about it.

> 
> The definition on the "Compiler" is an excellent example of what I want.
> A description of gcc might well start with that definition (edited 
> perhaps), then follow up:
>    The program gcc is a compiler for programs written in C programming
>    language. The C language is described in ...  
> 

But gcc is not a "compiler for programs written in C" - it is a compiler
for a variety of languages (C, C++, java, go, fortran, Ada - IIRC), a
run-time library (/not/ the standard C library, but the compiler support
library), and a driver program that will also invoke assemblers and
linkers as needed.


> Gnu is right to call their work a collection. It is really a fiction 
> that gcc is a free-standing program. 

Gnu call it a "compiler collection" because it is a collection of
compilers for different languages.  No one has ever thought of it as a
free-standing program, even when it was a pure C compiler - compilers
are very rarely single programs.

The program "gcc" itself is not even the compiler - it is a "driver"
program that passes data and options around amongst the various parts of
the suite to handle compilation and (usually) assembly and linking.

> There are two parts - the front 
> and back ends.

Three parts - there is also the "middle end".  (And the assembler and
linker come in addition - they are normally from binutils rather than gcc.)

> The front end produces a "source program" in an 
> intermediate language which the back end "assembles" into machine code.

Nope.  The "front end" is specific to the source code language, such as
C, C++, Fortran, etc.  It produces an intermediate language (GIMPLE),
which is passed on to the "middle end" where much of the optimisation
work takes place.

The middle-end is /mostly/ independent of both the back-end target and
the front-end language, but there is a certain amount of cross-talk
between the parts.  (llvm has a similar theoretical structure, but has
much cleaner separation between the parts.).  The output from the
middle-end is another intermediate language (RTL).

The back-end handles the target-specific register allocation and code
generation.  The result is assembly, not machine code - an external
assembler (usually "gas" from binutils) is called to generate the
machine code.  Then another external program (usually "ln" from
binutils) is called to link the object code and static libraries into an
executable.

(Things are a little more complicated when using link-time optimisation,
but lets skip that for now.)

> GNU, I believe, uses a Lisplike language called RTL. One way to make
> gcc a true program would be to make the back end a subroutine called at
> the end of front processing. A pipe might be a better idea.   
> 

Pipes /are/ the usual way of passing data and options between the passes
inside gcc.  Intermediary files are only stored if you ask for them
(typically for debugging gcc itself).

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Thread

Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-01 17:55 -0700
  Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-01 19:41 -0700
  Re: Understandability wssimms@gmail.com - 2015-05-01 20:45 -0700
  Re: Understandability Bartc <bc@freeuk.com> - 2015-05-02 10:38 +0100
    Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-02 09:15 -0700
      Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-04 09:26 +0200
        Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-04 12:52 -0700
  Re: Understandability Noob <root@127.0.0.1> - 2015-05-02 14:21 +0200
    Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-02 09:13 -0700
      Re: Understandability Ian Collins <ian-news@hotmail.com> - 2015-05-03 08:07 +1200
      Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-02 13:11 -0700
        Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-03 10:50 -0700
          Re: Understandability Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-03 13:26 -0700
            Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-04 12:29 -0700
              Re: Understandability Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-05 05:47 -0700
        Re: Understandability raltbos@xs4all.nl (Richard Bos) - 2015-05-08 21:10 +0000
          Re: Understandability Ian Collins <ian-news@hotmail.com> - 2015-05-09 09:17 +1200
          Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-08 14:32 -0700
            Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-09 09:13 -0700
              Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-09 16:48 -0700
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-10 11:05 -0700
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-11 08:48 +0200
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-11 09:55 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-11 17:52 -0400
                Re: Understandability glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-11 22:54 +0000
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-12 08:49 +0200
                Re: Understandability Morris Dovey <mrdovey@iedu.com> - 2015-05-12 02:15 -0500
                Re: Understandability Phil Carmody <pc+usenet@asdf.org> - 2015-05-25 03:15 +0300
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-25 00:45 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-25 10:26 -0700
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-11 10:06 -0700
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-12 08:59 +0200
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-12 08:37 -0700
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-13 08:53 +0200
                Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-13 08:16 -0700
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-13 09:49 -0700
                Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-13 10:53 -0700
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-14 10:35 -0700
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-13 09:31 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-13 13:10 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-14 10:27 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-14 22:51 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-15 10:02 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-15 13:37 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-16 09:18 -0700
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-16 23:56 +0200
                Re: Understandability gazelle@shell.xmission.com (Kenny McCormack) - 2015-05-17 12:45 +0000
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-17 09:16 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-17 12:47 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-18 10:54 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-18 15:00 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-19 09:49 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-19 13:10 -0400
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-16 19:01 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-17 09:30 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-17 12:58 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-18 10:54 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-18 14:56 -0400
                Re: Understandability David Kleinecke <dkleinecke@gmail.com> - 2015-05-19 09:46 -0700
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-19 13:16 -0400
                Re: Understandability Richard Heathfield <rjh@cpax.org.uk> - 2015-05-19 18:23 +0100
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-19 14:02 -0400
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-19 00:11 +0200
                Re: Understandability James Kuyper <jameskuyper@verizon.net> - 2015-05-18 18:28 -0400
                Re: Understandability Keith Thompson <kst-u@mib.org> - 2015-05-15 10:52 -0700
                Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-13 21:53 +0200
          Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-09 16:18 +0200
          Re: Understandability Noob <root@127.0.0.1> - 2015-05-09 18:31 +0200
            Re: Understandability raltbos@xs4all.nl (Richard Bos) - 2015-05-17 10:44 +0000
              Re: Understandability glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-17 15:53 +0000
      Re: Understandability David Brown <david.brown@hesbynett.no> - 2015-05-04 09:15 +0200
        Re: Understandability Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-05-16 00:28 +0000
  Re: Understandability Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-03 10:58 -0700

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