[LLVMdev] RFC: Upcoming Build System Changes

[Óscar Fuentes]

greened at obbligato.org (David A. Greene) writes:

> Joachim Durchholz <jo at durchholz.org> writes:
>
>> On the reasons why make-based builds are slow, Peter Miller has some 
>> insight to offer:
>> http://miller.emu.id.au/pmiller/books/rmch/ .
>> I'm not sure how widely recognized that paper is. Maybe it's widely 
>> known and today's build times stem from other things than recursive make.
>
> The paper is widely recognized.  Its lessons, unfortunatly, are not.
>
> Chris is absolutely on-target as to why the current build is slow.  It's
> slow because recursive make hides the parallelism.  It hides the
> parallelism because it hides the dependencies.  There is no way to get
> around that problem with a recursive make build system.

You keep repeating that and I say that it is wrong. Can you mention a
serialization point on the LLVM build caused by recursive make?
(GenLibDeps is not such example, as described on a previous message.)

[snip]