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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Baby X is bor nagain
Date: Mon, 24 Jun 2024 00:52:28 +0100
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On 23/06/2024 22:09, bart wrote:
> On 23/06/2024 19:21, bart wrote:
>> On 23/06/2024 13:25, David Brown wrote:
> 
>>> In my experience, programs don't usually consist of a single C file. 
>>> And if they do, build time is rarely long enough to worry anyone.
>>>
>>> I think, from the history of discussions in this group, that it is 
>>> more likely that your codebases are the peculiar ones.
>>
>>
>> I specifically excluded any of my own. I tried a variety of distinct 
>> projects, all sharing the same characteristics: that -O3 generally 
>> doubled build time, sometimes a bit less, often a lot more.
>>
>> But you seem remarkably unbothered that in your code-base, the 
>> difference is only 15% [for -O2]. I'd be quite curious.
>>
>> If that really was typical, and I was in charge of gcc, I'd seriously 
>> consider whether to bother with the -O0 and -O1 levels.
>>
>> However the following timings to build TCC/lUA are typical of my 
>> experience of gcc over 10-20 years:
>>
>>     (tcc  0.10)
>>     -O0   2.84 seconds to build tcc.exe
>>     -O1   5.70
>>     -O2  10.78
>>     -O3  13.21
>>
>>     (tcc  0.25)
>>     -O0   7.74 seconds to build lua.exe
>>     -O1  10.63
>>     -O2  14.95
>>     -O3  18.24
>>
>> I've shown the timings from building with Tcc to give some 
>> perspective. The proportional difference between -O3 and -O0 is indeed 
>> small compared with that between -O0 and tcc!
> 
> I've done one more test, which is compiling 140 .c files of Seed7 to 
> object files (not linking). This was done under WSL and outside of a 
> makefile where there were a million things going on that I had no idea 
> about.
> 
> Results were:
> 
>    -O0   17 seconds
>    -O2   36 seconds
>    -O3   43 seconds
> 
> This was done with one invocation of gcc. Invoking gcc each time might 
> well make it slower, but a test I did along those lines was not conclusive.
> 
> So, if the difference between O0 and O2 is so narrow for you, and it's 
> not the source code, nor how you invoke gcc, then there must be other 
> things going on.
> 
> 
43 seconds compile time is getting to be a bit of a problem. But not for 
the final build. Only for intermediate builds.
-- 
Check out my hobby project.
http://malcolmmclean.github.io/babyxrc