[clang] [llvm] Enable ClangIR Build By Default (PR #221291)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > > > At the moment it looks between 1-2%, would there be an acceptable increase, or does the artifact size make it just completely untenable?
> > > 
> > > 
> > > A 1-2% increase in startup time would be unproblematic -- what I'm actually seeing in local tests is a ~20% increase in wall-time when running clang on `int main() { return 0; }` (which should be about representative of `./configure` use cases...) with a dylib release build.
> > 
> > 
> > Interesting, I am not seeing the 20% increase, but I'm deep into trying to mess with CMake to minimize the startup time. I'd be interested in seeing if the patch I'm working on makes a difference if you'd be able/willing to test it.
> 
> I did this one: #232409
> 
> It reduces the overhead at load time to a reasonable amount as far as I can tell, but I'd love to see if it satisifies your concerns (regarding run-time).

Actually, I THINK I have helped the libclang-cpp.so size significantly.  WITH that other patch:

No ClangiR: 86.4mb
WITH 232409 patch: 127.6mb (~47.7% increase)
WITHOUT  it: 159.5mb    (~84.6% increase)


So I at least picked up some?  Probably not enough for Fedora I suspect, but hopefully it gets us significantly 'closer'.

https://github.com/llvm/llvm-project/pull/221291