If we run on a system with Xcode installed to a default path, run Xcode
Metal shader compiler to validate the generated MSL shader.
This uncovers an issue in the existing MSL test - MSL backend currently
does not auto-assign attribute locations, which means that translating
GLSL shader without location layout produces an invalid MSL which
generates "error: 'attribute' index '0' is used more than once".
To extract a column from row-major matrix, we need to do a strided load one
component at a time. In this case flattened_access_chain_offset still returns
the offset to the first element, but the stride is equal to matrix stride
instead of vector stride.
For this to work, we need to pass matrix stride (and transpose flag) through,
similar to how matrix flattening works.
Additionally slightly clean up recursive flattened_access_chain structure -
specifically, instead of deciding mid-traversal that we need matrix stride
information, we can just pass the matrix stride through - for access chains
that end in matrix/vector this gets us what we need, and for access chains
that end in structs the flattened_access_chain_struct code will recompute
correct stride/transposition data to pass through further.
Don't emit automatic sampler when using texture read().
Convert tex coords to uintN() when using texture read().
Emit face when read()ing cube textures.
Do not emit function prototypes. If secondary functions are used,
suppress compiler -Wmissing-prototypes warnings.
Refactor Compiler::emit_function_prototype() functions to simplify.
Rename Compiler_msl::CustomFunctionHandler to OpCodePreprocessor, and
Compiler_msl::register_custom_functions() to preprocess_op_codes()
to perform more generic preprocessing.
Add space between dynamic header lines and fixed header lines.