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Adding an explicit launch_bounds(1024) attribute for GPU kernels.

Deven Desai requested to merge deven-amd/eigen:rocm_launch_bounds_attribute_update into master

Starting with ROCm 3.5, the HIP compiler will change from HCC to hip-clang.

This compiler change introduce a change in the default value of the __launch_bounds__ attribute associated with a GPU kernel. (default value means the value assumed by the compiler as the __launch_bounds attribute__ value, when it is not explicitly specified by the user)

Currently (i.e. for HIP with ROCm 3.3 and older), the default value is 1024. That changes to 256 with ROCm 3.5 (i.e. hip-clang compiler). As a consequence of this change, if a GPU kernel with a __luanch_bounds__ attribute of 256 is launched at runtime with a threads_per_block value > 256, it leads to a runtime error. This is leading to a couple of Eigen unit test failures with ROCm 3.5.

This commit adds an explicit __launch_bounds(1024)__ attribute to every GPU kernel that currently does not have it explicitly specified (and hence will end up getting the default value of 256 with the change to hip-clang)

/cc @rmlarsen1

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