Debugging failures in TF/TFLite integration tests.

These are steps to reproduce/address failures in TF/TFLite integration tests. These instructions are most stable on Linux, though they may work with a few tweaks on Windows and macOS.

All steps here assume starting from the IREE root directory.

1. First create a Python virtual environment to install packages into:

   python -m venv iree-tf.venv
   source iree-tf.venv/bin/activate
   
   # Install test requirements
   python -m pip install -r ./integrations/tensorflow/test/requirements.txt
   

2. Install IREE's tools and Python bindings or build them from source

   Install distributed packages

   # Install packages from nightly releases
   # This should work for most cases, as the importers change infrequently
   python -m pip install \
     iree-compiler iree-runtime iree-tools-tf iree-tools-tflite \
     --find-links https://openxla.github.io/iree/pip-release-links.html
   

   OR build from source

   # Build Python bindings from source
   cmake -G Ninja -B ../iree-build/ -DIREE_BUILD_PYTHON_BINDINGS=ON .
   cmake --build ../iree-build/
   
   # Add IREE built-from-source Python packages to PYTHONPATH
   source .env
   
   # Install IREE TF/TFLite Python packages
   python -m pip install integrations/tensorflow/python_projects/iree_tf
   python -m pip install integrations/tensorflow/python_projects/iree_tflite
   

3. Run the python test command line

   The command can be obtained from the run file. For example, if iree_tfl_tests/llvmcpu_posenet_i8.run failed,

   cd integrations/tensorflow/test/
   cat iree_tfl_tests/llvmcpu_posenet_i8.run
   
   # REQUIRES: llvmcpu
   # RUN: %PYTHON -m iree_tfl_tests.posenet_i8_test --target_backend=llvmcpu --artifacts_dir=%t
   
   cd python/
   python -m iree_tfl_tests.posenet_i8_test --target_backend=llvmcpu --artifacts_dir=/tmp/posenet_i8_failure
   

   Note that the command can only be run under integrations/tensorflow/test/python directory.

4. Extract intermediate files and use with native tools

   The test will create an iree_input.mlir in the temp directory specified. Those can then be fed into iree-compile (built locally to reproduce the error)

   iree-compile \
     --iree-hal-target-backends=llvm-cpu \
     --iree-input-type=mhlo \
     iree_input.mlir