You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
58 lines
2.2 KiB
XML
58 lines
2.2 KiB
XML
7 years ago
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!--
|
||
|
|
Copyright (c) 2017 OpenPOWER Foundation
|
||
|
|
|
||
|
|
Licensed under the Apache License, Version 2.0 (the "License");
|
||
|
|
you may not use this file except in compliance with the License.
|
||
|
|
You may obtain a copy of the License at
|
||
|
|
|
||
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
||
|
|
|
||
|
|
Unless required by applicable law or agreed to in writing, software
|
||
|
|
distributed under the License is distributed on an "AS IS" BASIS,
|
||
|
|
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||
|
|
See the License for the specific language governing permissions and
|
||
|
|
limitations under the License.
|
||
|
|
|
||
|
|
-->
|
||
|
|
<section xmlns="http://docbook.org/ns/docbook"
|
||
|
|
xmlns:xi="http://www.w3.org/2001/XInclude"
|
||
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
|
|
version="5.0"
|
||
|
|
xml:id="sec_prefered_methods">
|
||
|
7 years ago
|
<title>Preferred methods</title>
|
||
|
7 years ago
|
|
||
|
|
<para>As we will see there are multiple ways to implement the logic of
|
||
|
|
these intrinsics. Some implementation methods are preferred because they allow
|
||
|
|
the compiler to select instructions and provided the most flexibility for
|
||
|
|
optimization across the whole sequence. Other methods may be required to
|
||
|
|
deliver a specific semantic or to deliver better optimization than the current
|
||
|
|
compiler is capable of. Some methods are more portable across multiple
|
||
|
|
compilers (GCC, LLVM, ...). All of this should be taken into consideration for
|
||
|
|
each intrinsic implementation. In general we should use the following list as a
|
||
|
|
guide to these decisions:</para>
|
||
|
|
|
||
|
7 years ago
|
<orderedlist spacing="compact">
|
||
|
7 years ago
|
<listitem>
|
||
|
|
<para>Use C vector arithmetic, logical, dereference, etc., operators in
|
||
|
|
preference to intrinsics.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>Use the bi-endian interfaces from Appendix A of the ABI in
|
||
|
|
preference to other intrinsics when available, as these are designed for
|
||
|
|
portability among compilers.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>Use other, less well documented intrinsics (such as
|
||
|
|
<literal>__builtin_vsx_*</literal>) when no better facility is available, in preference to
|
||
|
|
assembly.</para>
|
||
|
|
</listitem>
|
||
|
|
<listitem>
|
||
|
|
<para>If necessary, use inline assembly, but know what you're
|
||
|
|
doing.</para>
|
||
|
|
</listitem>
|
||
|
|
</orderedlist>
|
||
|
|
|
||
|
|
</section>
|
||
|
|
|