[clang] [libc] [Clang] Add handlers for 'match_any' and 'match_all' to `gpuintrin.h` (PR #127504)

[Joseph Huber via cfe-commits]

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@@ -162,6 +162,62 @@ __gpu_shuffle_idx_u64(uint64_t __lane_mask, uint32_t __idx, uint64_t __x,
          ((uint64_t)__gpu_shuffle_idx_u32(__lane_mask, __idx, __lo, __width));
 }
 
+// Returns a bitmask marking all lanes that have the same value of __x.
+_DEFAULT_FN_ATTRS static __inline__ uint64_t
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jhuber6 wrote:

Honestly I got confused myself whether or not the return value was a number or a mask. I think that having a `typedef uint64_t __lanemask_t` would be helpful for keeping that unambiguous, but  I think that it's best just to keep it `uint64_t` for all targets to simplify code and keep it portable. I might do that in a follow-up patch.

https://github.com/llvm/llvm-project/pull/127504