[clang] 025988d - Specify Clang vector builtins.
Florian Hahn via cfe-commits
cfe-commits at lists.llvm.org
Tue Oct 26 07:37:07 PDT 2021
Author: Florian Hahn
Date: 2021-10-26T15:34:31+01:00
New Revision: 025988ded6b2a57022dbf9775f35a1a933584bfa
URL: https://github.com/llvm/llvm-project/commit/025988ded6b2a57022dbf9775f35a1a933584bfa
DIFF: https://github.com/llvm/llvm-project/commit/025988ded6b2a57022dbf9775f35a1a933584bfa.diff
LOG: Specify Clang vector builtins.
This patch specifies a set of vector builtins for Clang, as discussed on
cfe-dev:
https://lists.llvm.org/pipermail/cfe-dev/2021-September/068999.html
https://lists.llvm.org/pipermail/cfe-dev/2021-October/069070.html
Reviewed By: scanon
Differential Revision: https://reviews.llvm.org/D111529
Added:
Modified:
clang/docs/LanguageExtensions.rst
Removed:
################################################################################
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 74f8f3dc3551..38443cee1935 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -506,6 +506,83 @@ See also :ref:`langext-__builtin_shufflevector`, :ref:`langext-__builtin_convert
If it's an extension (OpenCL) vector, it's only available in C and OpenCL C.
And it selects base on signedness of the condition operands (OpenCL v1.1 s6.3.9).
+Vector Builtins
+---------------
+
+**Note: The implementation of vector builtins is work-in-progress and incomplete.**
+
+In addition to the operators mentioned above, Clang provides a set of builtins
+to perform additional operations on certain scalar and vector types.
+
+Let ``T`` be one of the following types:
+
+* an integer type (as in C2x 6.2.5p19), but excluding enumerated types and _Bool
+* the standard floating types float or double
+* a half-precision floating point type, if one is supported on the target
+* a vector type.
+
+For scalar types, consider the operation applied to a vector with a single element.
+
+*Elementwise Builtins*
+
+Each builtin returns a vector equivalent to applying the specified operation
+elementwise to the input.
+
+Unless specified otherwise operation(±0) = ±0 and operation(±infinity) = ±infinity
+
+========================================= ================================================================ =========================================
+ Name Operation Supported element types
+========================================= ================================================================ =========================================
+ T __builtin_elementwise_abs(T x) return the absolute value of a number x; the absolute value of signed integer and floating point types
+ the most negative integer remains the most negative integer
+ T __builtin_elementwise_ceil(T x) return the smallest integral value greater than or equal to x floating point types
+ T __builtin_elementwise_floor(T x) return the largest integral value less than or equal to x floating point types
+ T __builtin_elementwise_roundeven(T x) round x to the nearest integer value in floating point format, floating point types
+ rounding halfway cases to even (that is, to the nearest value
+ that is an even integer), regardless of the current rounding
+ direction.
+ T__builtin_elementwise_trunc(T x) return the integral value nearest to but no larger in floating point types
+ magnitude than x
+ T __builtin_elementwise_max(T x, T y) return x or y, whichever is larger integer and floating point types
+ T __builtin_elementwise_min(T x, T y) return x or y, whichever is smaller integer and floating point types
+========================================= ================================================================ =========================================
+
+
+*Reduction Builtins*
+
+Each builtin returns a scalar equivalent to applying the specified
+operation(x, y) as recursive even-odd pairwise reduction to all vector
+elements. ``operation(x, y)`` is repeatedly applied to each non-overlapping
+even-odd element pair with indices ``i * 2`` and ``i * 2 + 1`` with
+``i in [0, Number of elements / 2)``. If the numbers of elements is not a
+power of 2, the vector is widened with neutral elements for the reduction
+at the end to the next power of 2.
+
+Example:
+
+.. code-block:: c++
+
+ __builtin_reduce_add([e3, e2, e1, e0]) = __builtin_reduced_add([e3 + e2, e1 + e0])
+ = (e3 + e2) + (e1 + e0)
+
+
+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_add(VT a) \+ integer and floating point types
+ ET __builtin_reduce_and(VT a) & integer types
+ ET __builtin_reduce_or(VT a) \| integer types
+ ET __builtin_reduce_xor(VT a) ^ integer types
+======================================= ================================================================ ==================================
+
Matrix Types
============
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