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| <refentry> |
| <refentryinfo> |
| <keywordset> |
| <keyword>Specifying Attribute For Unrolling Loops</keyword> |
| </keywordset> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>Specifying Attribute For Unrolling Loops</refentrytitle> |
| |
| <refmiscinfo> |
| <copyright> |
| <year>2007-2013</year> |
| <holder>The Khronos Group Inc. |
| Permission is hereby granted, free of charge, to any person obtaining a |
| copy of this software and/or associated documentation files (the |
| "Materials"), to deal in the Materials without restriction, including |
| without limitation the rights to use, copy, modify, merge, publish, |
| distribute, sublicense, and/or sell copies of the Materials, and to |
| permit persons to whom the Materials are furnished to do so, subject to |
| the condition that this copyright notice and permission notice shall be included |
| in all copies or substantial portions of the Materials.</holder> |
| </copyright> |
| </refmiscinfo> |
| <manvolnum>3</manvolnum> |
| </refmeta> |
| |
| <!-- ================================ SYNOPSIS --> |
| |
| <refnamediv id="AttributesofBlocksandControl-Flow-Statements"> |
| <refname>Specifying Attribute For Unrolling Loops</refname> |
| |
| <refpurpose> |
| Specifying Attribute For Unrolling Loops. |
| </refpurpose> |
| </refnamediv> |
| |
| <!-- ALTERNATIVE SYNTAX SYNOPSIS (NON-FUNCTION) --> |
| |
| <refsect2 id="synopsis"> |
| <title> |
| </title> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint)) |
| </entry> |
| </row> |
| |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint(n))) |
| </entry> |
| </row> |
| |
| </tbody> |
| </tgroup> |
| </informaltable> |
| </refsect2> |
| |
| <!-- ================================ DESCRIPTION --> |
| |
| <refsect1 id="description"><title>Description</title> |
| <para> |
| The <code>__attribute__((opencl_unroll_hint))</code> |
| and <code>__attribute__((opencl_unroll_hint(n)))</code> |
| attribute qualifiers can be used to specify that a loop |
| (<code>for</code>, <code>while</code> and <code>do</code> loops) |
| can be unrolled. This attribute qualifier can be |
| used to specify full unrolling or partial unrolling |
| by a specified amount. This is a compiler hint |
| and the compiler may ignore this directive. |
| </para> |
| |
| <para> |
| <code>n</code> is the loop unrolling factor and must |
| be a positive integral compile time constant expression. |
| An unroll factor of 1 disables unrolling. If |
| <code>n</code> is not specified, the compiler determines the |
| unrolling factor for the loop. |
| </para> |
| |
| <para> |
| NOTE: The <code>__attribute__((opencl_unroll_hint(n)))</code> |
| attribute qualifier must |
| appear immediately before the loop to be affected. |
| </para> |
| </refsect1> |
| |
| <!-- ================================ EXAMPLE --> |
| <!-- DO NOT DELETE IN CASE AN EXAMPLE IS ADDED IN THE FUTURE --> |
| |
| <refsect2 id="example1"> |
| <title> |
| Examples |
| </title> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint(2))) |
| while (*s != 0) |
| *p++ = *s++; |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| This tells the compiler to unroll the above while loop by a factor of 2. |
| </para> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint)) |
| for (int i=0; i<2; i++) |
| { |
| … |
| } |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| In the example above, the compiler will determine how much to unroll the loop. |
| </para> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint(1))) |
| for (int i=0; i<32; i++) |
| { |
| … |
| } |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| The above is an example where the loop should not be unrolled. |
| </para> |
| |
| <para> |
| Below are some examples of invalid usage of |
| <code>__attribute__((opencl_unroll_hint(n)))</code>. |
| </para> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint(-1))) |
| while (…) |
| { |
| … |
| } |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| The above example is an invalid usage of the loop unroll |
| factor as the loop unroll factor is negative. |
| </para> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __attribute__((opencl_unroll_hint)) |
| if (…) |
| { |
| … |
| } |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| The above example is invalid because the unroll |
| attribute qualifier is used on a non-loop |
| construct. |
| </para> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| kernel void |
| my_kernel( … ) |
| { |
| int x; |
| __attribute__((opencl_unroll_hint(x)) |
| for (int i=0; i<x; i++) |
| { |
| … |
| } |
| } |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| |
| <para> |
| The above example is invalid because the loop unroll |
| factor is not a compile-time constant expression. |
| </para> |
| </refsect2> |
| |
| |
| <!-- ================================ SPECIFICATION --> |
| <!-- Set the "uri" attribute in the <olink /> element to the "named destination" for the PDF page |
| --> |
| <refsect1 id="specification"><title>Specification</title> |
| <para> |
| <imageobject> |
| <imagedata fileref="pdficon_small1.gif" format="gif" /> |
| </imageobject> |
| |
| <olink uri="attributes-loopUnroll">OpenCL Specification</olink> |
| </para> |
| </refsect1> |
| |
| <!-- ================================ ALSO SEE --> |
| |
| <refsect1 id="seealso"><title>Also see</title> |
| <para> |
| <citerefentry href="attribute"><refentrytitle>__attribute__</refentrytitle></citerefentry>, |
| <citerefentry href="attributes-types"><refentrytitle>Type Attributes</refentrytitle></citerefentry>, |
| <citerefentry href="attributes-variables"><refentrytitle>Variable Attributes</refentrytitle></citerefentry> |
| </para> |
| </refsect1> |
| |
| <!-- ============================== COPYRIGHT --> |
| <!-- Content included from copyright.inc.xsl --> |
| |
| <refsect3 id="Copyright"><title></title> |
| <imageobject> |
| <imagedata fileref="KhronosLogo.jpg" format="jpg" /> |
| </imageobject> |
| <para /> |
| </refsect3> |
| |
| <!-- 12-Dec-2013, rev. 19 --> |
| </refentry> |
| |