[LLVMdev] avoid creating .dir files

[Dan Villiom Podlaski Christiansen]

On 20 Jan 2009, at 00:04, Mike Stump wrote:

> On Jan 19, 2009, at 1:58 PM, Chris Lattner wrote:
>> On Jan 19, 2009, at 10:02 AM, Mike Stump wrote:
>>
>>> There isn't a good reason to create files called .dir in the
>>> installation directory.  This patch fixes that.
>>
>> If we don't have this line, every build with do the makedir.
>
> And?
>
> $ time mkdir -p /bin
>
> real	0m0.002s
> user	0m0.000s
> sys	0m0.002s
>
> an extra mkdir takes around 2ms per build.  An up-to-date inc build
> takes 2231ms for me.  If you want some of the extra 2231ms back, I'd
> recommend avoiding recursion in the makefiles.  This will yield a
> larger benefit than worrying about the extra mkdir.

Not that it really matters, but do note that the LLVM build system  
uses ‘$(LLVM_SRC_ROOT)/autoconf/mkinstalldirs’ for MKDIR, rather  
than just ‘mkdir’.

> If we have it, then .dir files are created in the installation
> directories.
>
> Trivially one can do:
>
> /dir:
> 	mkdir /dir
>
> /dir/prog: /dir
> 	gcc hi.c -o /dir/prog
>
> and avoid the extra mkdir, if one wanted.  Any down side to doing  
> that?

Yes, ‘prog’ will be remade every time a file as added to or removed  
from the directory. (I haven't checked just now, but I'm fairly  
certain that's what will happen.) One way to solve this is by using an  
order-only dependancy:

/dir/prog: | /dir
	gcc hi.c -o /dir/prog

This will cause GNU Make to ensure that /dir is made _before_ /dir/ 
prog, but without invalidating the /dir/prog target when /dir is  
updated/invalidated.

Is it possible that I could get you to wait a bit with these changes?  
I just obtained commit access and set up a way to move over my changes  
from Mercurial to Subversion. I hope to have most of my changes to the  
build system integrated, and plan to post a proposal of how to get it  
done within the next few days or so.

Apart from a general overhaul of the Makefiles, I integrated Clang  
into much of the LLVM build system, for instance ‘llvm-config’.

--

Dan Villiom Podlaski Christiansen, stud. scient.,
danchr at cs.au.dk, danchr at gmail.com