Building and Iterating

[Brooks Davis]

On Fri, Jun 01, 2018 at 04:11:06PM -0600, Sean Bruno wrote:
> 
> 
> On 06/01/18 14:12, Brooks Davis wrote:
> > On Fri, Jun 01, 2018 at 11:20:22AM -0600, Sean Bruno wrote:
> >> 3.  If the boostrap toolchain needs to be built in the normal case, only
> >> target the ARCH being requested.  I understand that we "want" a CC
> >> installed that targets all architectures and this is something I agree with.
> > 
> > The LLVM backends are a tiny part of the LLVM build both in terms
> > of number of files and compile complexity.  Removing them would
> > require quite a bit of work (and ongoing maintenance) for a negliable
> > improvement.
> 
> Can you educate me on why its so hard to maintain this part of our
> tools?  I'm ignorant here and haven't looked to deeply into the abyss
> whereas you have been swimming in the darkness.

Because upstream makes absolutely no provision for this.  In our case we
do maintain the build infrastructure which would help a bit (since we
wouldn't be maintaining diffs to CMakeFiles), but it won't help at all
with the fact that any code can assume that all backends are there and
the constants associated with there are defined.  I'm not sure how big
that part is, but we'd certainly have some divergence to maintain.  IIRC
the backends are <5% of LLVM compile time.

IMO, the best way to avoid building LLVM as a bootstrap tool is to use
xtoolchain ports.  For i386 and amd64 I mostly use
CROSS_TOOLCHAIN=llvm60 (having installed xtoolchain-llvm60).  I think
there is still work to be done to make all of this more friendly (e.g.
I'd love an xtoolchain-universe12 metaport and a simple way to use it.)

-- Brooks
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