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[clang][docs] Revise documentation for __builtin_reduce_(max|min). #114637

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Nov 14, 2024
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[clang][docs] Revise documentation for __builtin_reduce_(max|min). #114637

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12 changes: 6 additions & 6 deletions clang/docs/LanguageExtensions.rst
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Expand Up @@ -745,12 +745,12 @@ Let ``VT`` be a vector type and ``ET`` the element type of ``VT``.
======================================= ====================================================================== ==================================
Name Operation Supported element types
======================================= ====================================================================== ==================================
ET __builtin_reduce_max(VT a) return x or y, whichever is larger; If exactly one argument is integer and floating point types
a NaN, return the other argument. If both arguments are NaNs,
fmax() return a NaN.
ET __builtin_reduce_min(VT a) return x or y, whichever is smaller; If exactly one argument integer and floating point types
is a NaN, return the other argument. If both arguments are
NaNs, fmax() return a NaN.
ET __builtin_reduce_max(VT a) return the largest element of the vector. If the element type is integer and floating point types
floating point, this function has the same comparison semantics as
``__builtin_reduce_maximum``.
ET __builtin_reduce_min(VT a) return the smallest element of the vector. If the element type is integer and floating point types
floating point, this function has the same comparison semantics as
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@arsenm arsenm Nov 5, 2024

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Looking at the implementation, this is going to use reduce_fmax intrinsic, which is not the same as reduce_maximum

I think this builtin trying to support floating point is an anti-feature, and if it has to, it should have matched minimum/maximum. But that's not what the implementation is doing

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``__builtin_reduce_minimum``.
ET __builtin_reduce_add(VT a) \+ integer types
ET __builtin_reduce_mul(VT a) \* integer types
ET __builtin_reduce_and(VT a) & integer types
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