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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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diff --git a/share/doc/gcc/Vector-Extensions.html b/share/doc/gcc/Vector-Extensions.html new file mode 100644 index 0000000..5cfb03e --- /dev/null +++ b/share/doc/gcc/Vector-Extensions.html @@ -0,0 +1,358 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Vector Extensions</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Vector Extensions"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Vector Extensions"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions"> +<link href="Offsetof.html#Offsetof" rel="next" title="Offsetof"> +<link href="Return-Address.html#Return-Address" rel="previous" title="Return Address"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Vector-Extensions"></a> +<div class="header"> +<p> +Next: <a href="Offsetof.html#Offsetof" accesskey="n" rel="next">Offsetof</a>, Previous: <a href="Return-Address.html#Return-Address" accesskey="p" rel="previous">Return Address</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Using-Vector-Instructions-through-Built_002din-Functions"></a> +<h3 class="section">6.52 Using Vector Instructions through Built-in Functions</h3> + +<p>On some targets, the instruction set contains SIMD vector instructions which +operate on multiple values contained in one large register at the same time. +For example, on the x86 the MMX, 3DNow! and SSE extensions can be used +this way. +</p> +<p>The first step in using these extensions is to provide the necessary data +types. This should be done using an appropriate <code>typedef</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); +</pre></div> + +<p>The <code>int</code> type specifies the <em>base type</em>, while the attribute specifies +the vector size for the variable, measured in bytes. For example, the +declaration above causes the compiler to set the mode for the <code>v4si</code> +type to be 16 bytes wide and divided into <code>int</code> sized units. For +a 32-bit <code>int</code> this means a vector of 4 units of 4 bytes, and the +corresponding mode of <code>foo</code> is <acronym>V4SI</acronym>. +</p> +<p>The <code>vector_size</code> attribute is only applicable to integral and +floating scalars, although arrays, pointers, and function return values +are allowed in conjunction with this construct. Only sizes that are +positive power-of-two multiples of the base type size are currently allowed. +</p> +<p>All the basic integer types can be used as base types, both as signed +and as unsigned: <code>char</code>, <code>short</code>, <code>int</code>, <code>long</code>, +<code>long long</code>. In addition, <code>float</code> and <code>double</code> can be +used to build floating-point vector types. +</p> +<p>Specifying a combination that is not valid for the current architecture +causes GCC to synthesize the instructions using a narrower mode. +For example, if you specify a variable of type <code>V4SI</code> and your +architecture does not allow for this specific SIMD type, GCC +produces code that uses 4 <code>SIs</code>. +</p> +<p>The types defined in this manner can be used with a subset of normal C +operations. Currently, GCC allows using the following operators +on these types: <code>+, -, *, /, unary minus, ^, |, &, ~, %</code>. +</p> +<p>The operations behave like C++ <code>valarrays</code>. Addition is defined as +the addition of the corresponding elements of the operands. For +example, in the code below, each of the 4 elements in <var>a</var> is +added to the corresponding 4 elements in <var>b</var> and the resulting +vector is stored in <var>c</var>. +</p> +<div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); + +v4si a, b, c; + +c = a + b; +</pre></div> + +<p>Subtraction, multiplication, division, and the logical operations +operate in a similar manner. Likewise, the result of using the unary +minus or complement operators on a vector type is a vector whose +elements are the negative or complemented values of the corresponding +elements in the operand. +</p> +<p>It is possible to use shifting operators <code><<</code>, <code>>></code> on +integer-type vectors. The operation is defined as following: <code>{a0, +a1, …, an} >> {b0, b1, …, bn} == {a0 >> b0, a1 >> b1, +…, an >> bn}</code>. Vector operands must have the same number of +elements. +</p> +<p>For convenience, it is allowed to use a binary vector operation +where one operand is a scalar. In that case the compiler transforms +the scalar operand into a vector where each element is the scalar from +the operation. The transformation happens only if the scalar could be +safely converted to the vector-element type. +Consider the following code. +</p> +<div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); + +v4si a, b, c; +long l; + +a = b + 1; /* a = b + {1,1,1,1}; */ +a = 2 * b; /* a = {2,2,2,2} * b; */ + +a = l + a; /* Error, cannot convert long to int. */ +</pre></div> + +<p>Vectors can be subscripted as if the vector were an array with +the same number of elements and base type. Out of bound accesses +invoke undefined behavior at run time. Warnings for out of bound +accesses for vector subscription can be enabled with +<samp>-Warray-bounds</samp>. +</p> +<p>Vector comparison is supported with standard comparison +operators: <code>==, !=, <, <=, >, >=</code>. Comparison operands can be +vector expressions of integer-type or real-type. Comparison between +integer-type vectors and real-type vectors are not supported. The +result of the comparison is a vector of the same width and number of +elements as the comparison operands with a signed integral element +type. +</p> +<p>Vectors are compared element-wise producing 0 when comparison is false +and -1 (constant of the appropriate type where all bits are set) +otherwise. Consider the following example. +</p> +<div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); + +v4si a = {1,2,3,4}; +v4si b = {3,2,1,4}; +v4si c; + +c = a > b; /* The result would be {0, 0,-1, 0} */ +c = a == b; /* The result would be {0,-1, 0,-1} */ +</pre></div> + +<p>In C++, the ternary operator <code>?:</code> is available. <code>a?b:c</code>, where +<code>b</code> and <code>c</code> are vectors of the same type and <code>a</code> is an +integer vector with the same number of elements of the same size as <code>b</code> +and <code>c</code>, computes all three arguments and creates a vector +<code>{a[0]?b[0]:c[0], a[1]?b[1]:c[1], …}</code>. Note that unlike in +OpenCL, <code>a</code> is thus interpreted as <code>a != 0</code> and not <code>a < 0</code>. +As in the case of binary operations, this syntax is also accepted when +one of <code>b</code> or <code>c</code> is a scalar that is then transformed into a +vector. If both <code>b</code> and <code>c</code> are scalars and the type of +<code>true?b:c</code> has the same size as the element type of <code>a</code>, then +<code>b</code> and <code>c</code> are converted to a vector type whose elements have +this type and with the same number of elements as <code>a</code>. +</p> +<p>In C++, the logic operators <code>!, &&, ||</code> are available for vectors. +<code>!v</code> is equivalent to <code>v == 0</code>, <code>a && b</code> is equivalent to +<code>a!=0 & b!=0</code> and <code>a || b</code> is equivalent to <code>a!=0 | b!=0</code>. +For mixed operations between a scalar <code>s</code> and a vector <code>v</code>, +<code>s && v</code> is equivalent to <code>s?v!=0:0</code> (the evaluation is +short-circuit) and <code>v && s</code> is equivalent to <code>v!=0 & (s?-1:0)</code>. +</p> +<a name="index-_005f_005fbuiltin_005fshuffle"></a> +<p>Vector shuffling is available using functions +<code>__builtin_shuffle (vec, mask)</code> and +<code>__builtin_shuffle (vec0, vec1, mask)</code>. +Both functions construct a permutation of elements from one or two +vectors and return a vector of the same type as the input vector(s). +The <var>mask</var> is an integral vector with the same width (<var>W</var>) +and element count (<var>N</var>) as the output vector. +</p> +<p>The elements of the input vectors are numbered in memory ordering of +<var>vec0</var> beginning at 0 and <var>vec1</var> beginning at <var>N</var>. The +elements of <var>mask</var> are considered modulo <var>N</var> in the single-operand +case and modulo <em>2*<var>N</var></em> in the two-operand case. +</p> +<p>Consider the following example, +</p> +<div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); + +v4si a = {1,2,3,4}; +v4si b = {5,6,7,8}; +v4si mask1 = {0,1,1,3}; +v4si mask2 = {0,4,2,5}; +v4si res; + +res = __builtin_shuffle (a, mask1); /* res is {1,2,2,4} */ +res = __builtin_shuffle (a, b, mask2); /* res is {1,5,3,6} */ +</pre></div> + +<p>Note that <code>__builtin_shuffle</code> is intentionally semantically +compatible with the OpenCL <code>shuffle</code> and <code>shuffle2</code> functions. +</p> +<p>You can declare variables and use them in function calls and returns, as +well as in assignments and some casts. You can specify a vector type as +a return type for a function. Vector types can also be used as function +arguments. It is possible to cast from one vector type to another, +provided they are of the same size (in fact, you can also cast vectors +to and from other datatypes of the same size). +</p> +<p>You cannot operate between vectors of different lengths or different +signedness without a cast. +</p> +<a name="index-_005f_005fbuiltin_005fshufflevector"></a> +<p>Vector shuffling is available using the +<code>__builtin_shufflevector (vec1, vec2, index...)</code> +function. <var>vec1</var> and <var>vec2</var> must be expressions with +vector type with a compatible element type. The result of +<code>__builtin_shufflevector</code> is a vector with the same element type +as <var>vec1</var> and <var>vec2</var> but that has an element count equal to +the number of indices specified. +</p> +<p>The <var>index</var> arguments are a list of integers that specify the +elements indices of the first two vectors that should be extracted and +returned in a new vector. These element indices are numbered sequentially +starting with the first vector, continuing into the second vector. +An index of -1 can be used to indicate that the corresponding element in +the returned vector is a don’t care and can be freely chosen to optimized +the generated code sequence performing the shuffle operation. +</p> +<p>Consider the following example, +</p><div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); +typedef int v8si __attribute__ ((vector_size (32))); + +v8si a = {1,-2,3,-4,5,-6,7,-8}; +v4si b = __builtin_shufflevector (a, a, 0, 2, 4, 6); /* b is {1,3,5,7} */ +v4si c = {-2,-4,-6,-8}; +v8si d = __builtin_shufflevector (c, b, 4, 0, 5, 1, 6, 2, 7, 3); /* d is a */ +</pre></div> + +<a name="index-_005f_005fbuiltin_005fconvertvector"></a> +<p>Vector conversion is available using the +<code>__builtin_convertvector (vec, vectype)</code> +function. <var>vec</var> must be an expression with integral or floating +vector type and <var>vectype</var> an integral or floating vector type with the +same number of elements. The result has <var>vectype</var> type and value of +a C cast of every element of <var>vec</var> to the element type of <var>vectype</var>. +</p> +<p>Consider the following example, +</p><div class="smallexample"> +<pre class="smallexample">typedef int v4si __attribute__ ((vector_size (16))); +typedef float v4sf __attribute__ ((vector_size (16))); +typedef double v4df __attribute__ ((vector_size (32))); +typedef unsigned long long v4di __attribute__ ((vector_size (32))); + +v4si a = {1,-2,3,-4}; +v4sf b = {1.5f,-2.5f,3.f,7.f}; +v4di c = {1ULL,5ULL,0ULL,10ULL}; +v4sf d = __builtin_convertvector (a, v4sf); /* d is {1.f,-2.f,3.f,-4.f} */ +/* Equivalent of: + v4sf d = { (float)a[0], (float)a[1], (float)a[2], (float)a[3] }; */ +v4df e = __builtin_convertvector (a, v4df); /* e is {1.,-2.,3.,-4.} */ +v4df f = __builtin_convertvector (b, v4df); /* f is {1.5,-2.5,3.,7.} */ +v4si g = __builtin_convertvector (f, v4si); /* g is {1,-2,3,7} */ +v4si h = __builtin_convertvector (c, v4si); /* h is {1,5,0,10} */ +</pre></div> + +<a name="index-vector-types_002c-using-with-x86-intrinsics"></a> +<p>Sometimes it is desirable to write code using a mix of generic vector +operations (for clarity) and machine-specific vector intrinsics (to +access vector instructions that are not exposed via generic built-ins). +On x86, intrinsic functions for integer vectors typically use the same +vector type <code>__m128i</code> irrespective of how they interpret the vector, +making it necessary to cast their arguments and return values from/to +other vector types. In C, you can make use of a <code>union</code> type: +</p><div class="smallexample"> +<pre class="smallexample">#include <immintrin.h> + +typedef unsigned char u8x16 __attribute__ ((vector_size (16))); +typedef unsigned int u32x4 __attribute__ ((vector_size (16))); + +typedef union { + __m128i mm; + u8x16 u8; + u32x4 u32; +} v128; +</pre></div> + +<p>for variables that can be used with both built-in operators and x86 +intrinsics: +</p> +<div class="smallexample"> +<pre class="smallexample">v128 x, y = { 0 }; +memcpy (&x, ptr, sizeof x); +y.u8 += 0x80; +x.mm = _mm_adds_epu8 (x.mm, y.mm); +x.u32 &= 0xffffff; + +/* Instead of a variable, a compound literal may be used to pass the + return value of an intrinsic call to a function expecting the union: */ +v128 foo (v128); +x = foo ((v128) {_mm_adds_epu8 (x.mm, y.mm)}); +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Offsetof.html#Offsetof" accesskey="n" rel="next">Offsetof</a>, Previous: <a href="Return-Address.html#Return-Address" accesskey="p" rel="previous">Return Address</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |