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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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Update LanguageExtensions.rst
c8ef Nov 2, 2024
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c8ef Nov 3, 2024
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8 changes: 2 additions & 6 deletions clang/docs/LanguageExtensions.rst
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Expand Up @@ -745,12 +745,8 @@ 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. integer and floating point types
ET __builtin_reduce_min(VT a) return the smallest element of the vector. integer and floating point types
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@RKSimon RKSimon Nov 3, 2024

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Please can you add back the NaN semantics - AFAICT they should always return the largest/smallest non-NAN value if any vector element is non-NAN, otherwise it could return any of the NAN values in the (all NAN) vector. There might be a better way of phrasing that......

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@c8ef c8ef Nov 3, 2024

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LLVM LangRef states: "This instruction has the same comparison semantics as the ‘llvm.maxnum.*’ intrinsic." Can I add a link to https://llvm.org/docs/LangRef.html#vector-reduction-intrinsics?

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@c8ef c8ef Nov 3, 2024

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Add pointers to the floating point min/max function.

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@arsenm arsenm Nov 5, 2024 •
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Do we have any kind of conformance testing for this?

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@c8ef c8ef Nov 6, 2024

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I'm not sure if we had any conformance testing before, but since this is just a document change and the patch is keeping the clang builtin document aligned with the llvm intrinsic document, maybe there's no need to add extra tests here?

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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