This is a series of fixes to the dynamic libraries we build / create to remove
any unnecessary bloat (unused architectures, bitcode).
A brand new watchOS app with no changes goes from 35MB to 11MB with these
fixes (with incremental builds disabled, the app size is 10MB).
--------------------------------------------------------------------------------
* [runtime] Split list of architectures into simulator and device-specific lists.
* [runtime] Build separate dylibs for device and simulator.
Build separate dylibs for device and simulator, since we already install these
into different locations.
This makes both the simulator and device builds slightly faster (since the
respective dylibs are smaller, and less data to copy around).
For watchOS apps, this saves ~430kb.
* [runtime] Strip bitcode from dylibs. Fixes#51352.
We know that dylibs will never be shipped to the App Store, so we'll never
need them to have bitcode.
So just strip the bitcode from all our dylibs, since this makes apps with
fastdev significantly smaller (and thus much faster to upload to watch
devices).
For watchOS apps this is a very significant improvement: a branch new watchOS
app without any changes goes from 35MB to 17MB.
https://bugzilla.xamarin.com/show_bug.cgi?id=51352
* [mtouch] Fix dylib compilation to not embed full bitcode.
Facts
=====
a. The output from the AOT compiler is an assembly (.s) file.
b. Clang's assembler does not support -fembed-bitcode-marker (only -fembed-
bitcode), so when we ask clang to -fembed-bitcode-marker, the assembler
receives a -fembed-bitcode argument.
c. This means that the assembled object file does not contain the
__LLVM/__bitcode and __LLVM/__cmdline sections (it does however contain an
__LLVM/__asm section).
d. The native linker will create a bitcode assembly section if none of the
object files passed to the linker contain a __LLVM/__bitcode section and
there's an __LLVM/__asm section present.
e. The end result is that when we build to a dylib, we end up (unexpectedly,
because we ask Clang to -fembed-bitcode-marker) including both armv7k and
bitcode in the dylib, thus bloating the dylib size significantly.
Solution
========
We manually add the __LLVM/__bitcode and __LLVM/__cmdline sections to the .s
file Mono's AOT compiler generated. This way the .o file will have the magic
sections, and the linker will not include bitcode (only the bitcode marker) in
the final library.
An empty watchOS extension with incremental builds is now 6MB smaller (down
to 11MB from 17MB).
0a07b6ba8e