[LLVMdev] Optional Target Builds

[Chris Lattner]

On Fri, 22 Apr 2005, Reid Spencer wrote:
> Okay, we need to get this resolved. So far we have two camps: (a) those
> that want the default to be "all" and (b) those that want the default to
> be "host-only". This is easy enough to change in the configure script;
> we just need to make a decision. So far we have:

Let me try to clarify why I feel the way I do.  For this discussion, I use 
the term "end-user" to be someone who just wants to USE a compiler, and 
doesn't want to hack on the compiler.


To me, the current LLVM distro isn't something that an end-user would 
generally want to use directly.  In particular, the LLVM CVS repo is 
currently biased towards supporting developers more than end-users.  For 
end-users, I think it would be most useful to build all of the targets, 
but only link the host target into llc (the others remain as .so files). 
That way the common case of non-cross-compiling will be fast (llc has a 
smaller disk footprint), but cross compilation can still work.

Since end users don't build the tree often (e.g. only once), they don't 
really care THAT much about LLVM build time.  More commonly, a packager 
will do this work for them, producing a set of debs, gentoo packages, etc.

The problem with building targets as .so files is transparency: you need 
to know to pass "-load libfoo.so" to llc to get support for the "foo" 
target.  In the long-term, I think this is 100% acceptable.  In 
particular, llc is a low-level developer tool that end-users will ideally 
not have to directly use in the future.  In particular, someday hopefully 
soon, end-users will interface to the llvm toolchain exclusively through 
the llvmc tool.  llvmc will fork off the subtools when necessary.

I think it's perfectly reasonable for llvmc to know which targets are 
linked into the llc tool and automatically provide the -load option when 
needed.


If you accept the above, then we have 3 classes of people to consider: 1. 
end-users with the above definition, 2. developers that want to test 
everything [including the nightly testers], and 3. developers who don't 
want to test everything.

I think that all groups of people are important, the only question is who 
passes the extra flag.  I think that "punishing" group #3 is the right way 
to go, because they're the ones that want to do something strange, and 
they're the ones that know enough about llvm to do it. :)

-Chris

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