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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: Baby X is bor nagain
Date: Mon, 24 Jun 2024 12:17:50 +0100
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On 24/06/2024 09:28, David Brown wrote:
> On 24/06/2024 02:56, Scott Lurndal wrote:
>> bart <bc@freeuk.com> writes:
>>> On 24/06/2024 00:52, Malcolm McLean wrote:
>>
>>>> 43 seconds compile time is getting to be a bit of a problem. But not 
>>>> for
>>>> the final build. Only for intermediate builds.
>>>
>>> That isn't the issue here (it could have been 4.3 seconds vs 1.7 
>>> seconds).
>>>
>>> David Brown was claiming there was little difference (15%, although on
>>> the 34.3s and 30.8s timings, it is actually 11% not 15%) between
>>> optimised and unoptimised builds, whereas I have always seen substantial
>>> differences like 100% or more.
> 
> I think the main problem is that Bart doesn't understand what "builds" 
> are.  And he doesn't understand the relevance - or irrelevance - of 
> compile times while developing software, and how they relate to /build/ 
> times or /development/ time.  I don't care how long it takes to compile 
> a file - I care how long the build takes.

I've been building programs for approaching half a century, and I've 
been developing tools do so for most of that.

Do you really thing I don't know what a 'build' is?

I can recreate a 13% difference between -O0 and -O2 on one project (not 
mine), which is 34 files that takes either 22 seconds or 25 seconds.

That is the one where SDL headers are used by most of the modules (where 
you claim that gcc will build them instantly if only I didn't use 
Windows). But it has been extablished that processing lots of headers is 
not affected by optimisation flags.

I noticed that my MCC compiler took 1.8 seconds for a full-build, which 
for me is annoyingly slow, considering the C code amounts to only 7Kloc.

But because this is C, I switched to incremental compilation, but done 
manually: setting up a project file for my IDE (instead of compiling 
*.c), where I can re-compile an individual file then link.

So that is always a possibility, and have used that in the past when my 
language had independent compilation.

With true whole-program compilation as I normally use, the problem 
simply wouldn't arise: the library interface, which would also be a 
short summary not dozens of sprawling headers, is processed once per build.