[clang] [Clang] Add builtins for masked vector loads / stores (PR #154464)

[Erich Keane via cfe-commits]

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@@ -941,6 +941,24 @@ Let ``VT`` be a vector type and ``ET`` the element type of ``VT``.
                                          for the comparison.
 ======================================= ====================================================================== ==================================
 
+*Masked Builtins*
+
+Each builtin accesses memory according to a provided boolean mask. These are
+provided as ``__builtin_masked_load`` and ``__builtin_masked_store``. The first
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erichkeane wrote:

Yep, crossed in the interwebs :) 

https://github.com/llvm/llvm-project/pull/154464