No __unorddf2 in NDK for aarch64

[DanAlbert]

__unorddf2 isn't in libgcc for aarch64, but clang emits calls for it when compiling some libc++ tests. One possible solution for this would be to switch to compiler-rt instead of libgcc, but that's not something that will happen for r15.

One such test: sources/cxx-stl/llvm-libc++/test/std/numerics/complex.number/complex.transcendentals/atan.pass.cpp

[DanAlbert]

Anyone else landing here: only real workaround would be to add a definition of these things to your code. The compiler-rt versions are dual MIT/University of Illinois Open Source licensed: https://android.googlesource.com/platform/external/compiler-rt/+/master/lib/builtins/muloti4.c

The only things that should be missing are some of the less commonly needed builtins (128-bit math).

[DanAlbert]

Upstream bug about this: https://llvm.org/bugs/show_bug.cgi?id=16404

[DanAlbert]

Good news is that the newer Clang (the one I'm verifying for r15 right now) doesn't emit __unorddf2 for the libc++ tests. There was some talk upstream of trying to avoid using things not available in libgcc, so maybe that happened? Or maybe those calls are just being inlined now. @stephenhines @pirama-arumuga-nainar, any idea?

[stephenhines]

They are probably just generating different code. I didn't spot anything that makes me believe that "inlining" is happening, since the calls would still be to a nonexistent compiler-rt set of builtins. This is a tricky problem that will likely keep recurring until we can properly switch over to using compiler-rt for builtins.

[pirama-arumuga-nainar]

We added unorddf2 to compiler_rt-extras (https://android-review.googlesource.com/#/c/243673/). Is that not included with the NDK?

[DanAlbert]

They are probably just generating different code.

Okay, I figured as much.

We added unorddf2 to compiler_rt-extras (https://android-review.googlesource.com/#/c/243673/). Is that not included with the NDK?

No, it isn't. We don't have control of our users' build systems, so something like compiler_rt-extras doesn't really work for us (we can try doing something with a linker script, but haven't yet).

[DanAlbert]

Moving to compiler-rt is somewhat non-trivial because it's difficult to get building for ICS. Moving to r17.

[fornwall]

@DanAlbert Is the plan still to move from libgcc to compiler-rt for r17?