adjust abseil version to be compatible between cmake tensorflowlite and bazel

[kruglov-dmitry]

At the moment version of libabseil library defined in bazel and cmake scripts are different:

Bazel will add those namespace prefix lts_2020_09_23 and cmake this one lts_2020_02_25.

In case you compile tensorflowlite library via cmake and build remaining libraries for tensorflow lite using bazel (for example libmetal-delegate) you can't use link them later as you will get unresolved symbols:

Unresolved symbol:

absl::lts_2020_09_23::UnknownError(absl::lts_2020_09_23::string_view), 
referenced from: tflite::gpu::metal::(anonymous namespace)::AllocateTensorMemory(
id<MTLDevice>,tflite::gpu::StrongShape<(tflite::gpu::Layout)12> const&, tflite::gpu::TensorDescriptor const&, void const*, id<MTLBuffer> __autoreleasing*, id<MTLTexture> __autoreleasing*) 
in libmetal_spatial_tensor.a(metal_spatial_tensor.o)

But, for libraries compiled by cmake (and used in tf lite):

nm ./tensorflow/lite/tf_build/_deps/abseil-cpp-build/absl/status/libabsl_status.a | grep UnknownError
0000000000003110 T __ZN4absl14lts_2020_02_2512UnknownErrorENS0_11string_viewE

absl::lts_2020_09_23::UnknownError(absl::lts_2020_09_23::string_view
vs
absl::lts_2020_02_25::UnknownError string_view

[terryheo]

We don't accept new change for 2.5 branch except cherry-picks. Could you check if the cherry-pick of 8348b34 resolves the issue?

[kruglov-dmitry]

I've cloned TF from scratch, switch on v2.5.0 and run

git cherry-pick 8348b348ac509c70a8730416be773781ddd6e2ed

After that file

• tensorflow/lite/tools/cmake/modules/abseil-cpp.cmake
  contains this hash:
  GIT_TAG 997aaf3a28308eba1b9156aa35ab7bca9688e9f6
  which resolved to

git describe --tags
20210324.0

• third_party/absl/workspace.bzl
  contains this hash:
  ABSL_COMMIT = "6f9d96a1f41439ac172ee2ef7ccd8edf0e5d068c"
  which is resolved to

git describe --tags
20200923.3

i.e. unfortunately it will still lead to mismatched symbols.

Just in case I've compiled libs for usage of metal delegate bia bazel and build tensorflowlite itself via cmake.

During compilation I've got unresolved symbols:

Undefined symbols for architecture arm64:
  "absl::lts_2020_09_23::UnknownError(absl::lts_2020_09_23::string_view)", referenced from:
      tflite::gpu::metal::(anonymous namespace)::AllocateTensorMemory(id<MTLDevice>, tflite::gpu::StrongShape<(tflite::gpu::Layout)12> const&, tflite::gpu::TensorDescriptor const&, void const*, id<MTLBuffer> __autoreleasing*, id<MTLTexture> __autoreleasing*) in libmetal_spatial_tensor.a(metal_spatial_tensor.o)

find tf_cherry_pick/_deps/ -iname '*.a' -exec nm -A {} \; | grep UnknownError
tf_cherry_pick/_deps//libabsl_status.a:status.cc.o: 0000000000002dc4 T __ZN4absl12lts_2021032412UnknownErrorENS0_11string_viewE

and tensorflowlite itself contains symbols from abseil 20210324 namespace

nm tf_cherry_pick/libtensorflow-lite.a | grep 20210324 | grep UnknownError
                 U __ZN4absl12lts_2021032412UnknownErrorENS0_11string_viewE

[mihaimaruseac]

We can merge this but only when we do a patch release on TF 2.5

[terryheo]

Linking Bazel generated binary with CMake looks strange a use-case.
If you can use the Bazel, why do you need to use CMake?

[kruglov-dmitry]

Thats a good question!

Bazel was a new beast for our team so we have started with old(?) good(?) cmake.

Along the way, specifically when we try to adopt delegates, we realise that not all artefacts are buildable by it,

• so I've to build missing dependencies using bazel and tried to figure out why they not match each other.

ps Thats probably offtopic here, but I would be more then happy to see how to
properly generate coreml related dependencies, as I've end up by building coremltool libs with specific version of protobuf
and patch few things to include missing symbols into libraries in order to get it working on device.