[LLVMdev] RFC: Upcoming Build System Changes

[Óscar Fuentes]

Wesley Peck <peckw at wesleypeck.com> writes:

> Just for informational purposes on a smaller system (Core 2 Duo MacBook Pro):

That's a dualcore laptop, isn't it?

[snip]

> One thing that I noticed (not in this table) was that tablegen is
> about 300% faster on my machine when building a Release build vs. a
> Debug build, lowering the build time for the X86.td rebuild from 46
> seconds to 15 seconds. This obviously adds up quickly when there are
> more tablegen files being regenerated.
>
> Perhaps tablegen should always be compiled with optimizations even in
> Debug Mode? I assume the need to debug tablegen itself is relatively
> rare.

The cmake build already supports building an extra tblgen for the build,
although that is currently used only when cross-compiling. I guess that
the Makefile-based build does the same. Expanding its application for
debug builds is simple, although some time measurements should be
performed before adding the feature. In the meantime, interested users
can set the LLVM_TABLEGEN variable, which allows to use an arbitrary
tblgen executable. So if you have an optimized tblgen around, you can
already use it for debug builds.