[clang][docs] Revise documentation for __builtin_reduce_(max|min).
#114637
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@llvm/pr-subscribers-clang Author: None (c8ef) ChangesFull diff: https://github.com/llvm/llvm-project/pull/114637.diff 1 Files Affected:
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 10232ff41da15a..b7676bab623ef8 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -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
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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clang/docs/LanguageExtensions.rst
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| 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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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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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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Add pointers to the floating point min/max function.
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Do we have any kind of conformance testing for this?
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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?
clang/docs/LanguageExtensions.rst
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| 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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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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I apologize for my earlier mistake. The function |
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@c8ef why did you close this? |
clang/docs/LanguageExtensions.rst
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| ET __builtin_reduce_max(VT a) return the largest element of the vector. The result will always be integer and floating point types | ||
| a number unless all elements of the vector are NaN. | ||
| ET __builtin_reduce_min(VT a) return the smallest element of the vector. The result will always be integer and floating point types | ||
| a number unless all elements of the vector are NaN. |
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The floating point result will always be a number unless all elements of the vector are NaN.?
| ET __builtin_reduce_max(VT a) return the largest element of the vector. The floating point result integer and floating point types | ||
| will always be a number unless all elements of the vector are NaN. | ||
| ET __builtin_reduce_min(VT a) return the smallest element of the vector. The floating point result integer and floating point types | ||
| will always be a number unless all elements of the vector are NaN. |
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This will not be true for a signaling nan for a 2 element vector with IEEE behavior for minnum/maxnum
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But really it was a mistake to make this support floating point
The function operation described in the document did not match its actual semantic meaning, this patch resolved the problem.