Android LTO: clang toolchain

[ruslo]

From Gitter:

after gcc didn't "just work", I tried clang quickly. for clang toolchains,
it is necessary to make symlinks from *.dylib files (to *.so) for OS X.

> cd android-ndk-r11c/toolchains/llvm/prebuilt/darwin-x86_64/lib64/
> ln -s LLVMgold.dylib LLVMgold.so

From android/ndk#108

[ruslo]

Got similar problem with clang-lto on Linux:

 /usr/bin/ld: /usr/lib/llvm-3.8/bin/../lib/LLVMgold.so: error loading
  plugin: /usr/lib/llvm-3.8/bin/../lib/LLVMgold.so: cannot open shared object
  file: No such file or directory

[ruslo]

Will start with android-ndk-r10e-api-16-armeabi-v7a-neon-clang-35-hid-sections-lto
(based on #310 (comment)).

[ruslo]

NDK fixes:

• NDK link-time optimization fails missing llvmgold.so, but contains llvmgold.dylib android/ndk#108 (comment)

Downloading r14...

[ruslo]

Example from NDK:

• https://android-review.googlesource.com/#/c/319310/4/tests/build/flto/CMakeLists.txt

[headupinclouds]

I will grab it. I believe this has a complete libc++ as well.

[ruslo]

Downloading r14...

Looks good!

Example from NDK

For armv7a there is no need to use -fuse-ld=gold but we need this for arm-v8a because of "format not recognized" error. -fuse-ld=gold works for armv7a too so I'm setting it unconditionally always for Clang, see branch https://github.com/ruslo/polly/commits/pr.android.lto:

• ruslo/polly@165aec9

[ruslo]

Will start with android-ndk-r10e-api-16-armeabi-v7a-neon-clang-35-hid-sections-lto
(based on #310 (comment)).

Adding NDK r14 variants of those toolchains:

• android-ndk-r14-api-21-arm64-v8a-clang-hid-sections-lto (Android LTO, Clang NDK r14, API {16,21} {armeabi-v7a, arm64-v8a}: OpenCV failed #343)
• android-ndk-r14-api-16-armeabi-v7a-neon-clang-hid-sections-lto (Android LTO, Clang NDK r14, API {16,21} {armeabi-v7a, arm64-v8a}: OpenCV failed #343)

[ruslo]

Toolchains is in Polly master now, closing.

[headupinclouds]

Thanks!

[headupinclouds]

I guess we just wait for NDK/LLVM updates for -Os now.