[clang] [AVX10][Doc] Add documentation about AVX10 options and their attentions (PR #77925)

[Simon Pilgrim via cfe-commits]

================
@@ -3963,6 +3963,60 @@ implicitly included in later levels.
 - ``-march=x86-64-v3``: (close to Haswell) AVX, AVX2, BMI1, BMI2, F16C, FMA, LZCNT, MOVBE, XSAVE
 - ``-march=x86-64-v4``: AVX512F, AVX512BW, AVX512CD, AVX512DQ, AVX512VL
 
+`Intel AVX10 ISA <https://cdrdv2.intel.com/v1/dl/getContent/784267>`_ is
+a major new vector ISA incorporating the modern vectorization aspects of
+Intel AVX-512. This ISA will be supported on all future Intel processor.
+Users are supposed to use the new options ``-mavx10.N`` and ``-mavx10.N-512``
+on these processors and do not use traditional AVX512 options anymore.
+
+The ``N`` in ``-mavx10.N`` represents a continuous integer number starting
+from ``1``. ``-mavx10.N`` is an alias of ``-mavx10.N-256``, which means to
+enable all instructions within AVX10 version N at a maximum vector length of
+256 bits. ``-mavx10.N-512`` enables all instructions at a maximum vector
+length of 512 bits, which is a superset of instructions ``-mavx10.N`` enabled.
+
+Current binaries built with AVX512 features can run on Intel AVX10/512 capable
+processor without re-compile, but cannot run on AVX10/256 capable processor.
+Users need to re-compile their code with ``-mavx10.N``, and maybe update some
+code that calling to 512-bit X86 specific intrinsics and passing or returning
+512-bit vector types in function call, if they want to run on AVX10/256 capable
+processor. Binaries built with ``-mavx10.N`` can run on both AVX10/256 and
+AVX10/512 capable processor.
+
+Users can add a ``-mno-evex512`` in the command line with AVX512 options if
+they want run the binary on both legacy AVX512 processor and new AVX10/256
+capable processor. The option has the same constraints as ``-mavx10.N``, i.e.,
+cannot call to 512-bit X86 specific intrinsics and pass or return 512-bit vector
+types in function call.
+
+Users should avoid to use AVX512 features in function target attributes when
+develop code for AVX10. If they have to do so, they need to add an explicit
+``evex512`` or ``no-evex512`` together with AVX512 features for 512-bit or
+non-512-bit functions respectively to avoid unexpected code generation. Both
+command line option and target attribute of EVEX512 feature can only be used
+with AVX512. They don't affect vector size of AVX10.
+
+User should not mix use AVX10 and AVX512 options together in any time, because
----------------
RKSimon wrote:

"Users should not mix the use AVX10 and AVX512 options together at any time,"

https://github.com/llvm/llvm-project/pull/77925