Fix LLVM target detection when cross-compiling. #57182
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Conditions like @bazel_tools//src/conditions:linux_aarch64 do not appear to be triggered correctly when cross-compiling on Linux. I'm guessing this is because TensorFlow does not yet use Bazel platforms and instead uses the older --cpu and --crosstool_top features. This means that we fall through to the default condition and end up building an x86-targeting LLVM even though we intended to target, say, aarch64. The symptom this causes is errors like: 'neoverse-n1' is not a recognized processor for this target (ignoring processor) '+neon' is not a recognized feature for this target (ignoring feature) '+fp-armv8' is not a recognized feature for this target (ignoring feature) '+crypto' is not a recognized feature for this target (ignoring feature) '+lse' is not a recognized feature for this target (ignoring feature) '+crc' is not a recognized feature for this target (ignoring feature) from XLA:CPU compilation. Take the same approach that has previously been used for Darwin ARM64 builds and add a new config_setting() for LLVM architecture detection that mirrors the definitions in //tensorflow/BUILD. Change tested both under x86->aarch64 cross compilation and aarch64 self-hosted compilation.
This was referenced Aug 16, 2022
chsigg
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Aug 19, 2022
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Conditions like @bazel_tools//src/conditions:linux_aarch64 do not
appear to be triggered correctly when cross-compiling on Linux. I'm
guessing this is because TensorFlow does not yet use Bazel platforms and
instead uses the older --cpu and --crosstool_top features.
This means that we fall through to the default condition and end up
building an x86-targeting LLVM even though we intended to target, say,
aarch64. The symptom this causes is errors like:
'neoverse-n1' is not a recognized processor for this target (ignoring
processor)
'+neon' is not a recognized feature for this target (ignoring feature)
'+fp-armv8' is not a recognized feature for this target (ignoring
feature)
'+crypto' is not a recognized feature for this target (ignoring feature)
'+lse' is not a recognized feature for this target (ignoring feature)
'+crc' is not a recognized feature for this target (ignoring feature)
from XLA:CPU compilation.
Take the same approach that has previously been used for Darwin ARM64
builds and add a new config_setting() for LLVM architecture detection
that mirrors the definitions in //tensorflow/BUILD.
Change tested both under x86->aarch64 cross compilation and aarch64
self-hosted compilation.