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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE appref SYSTEM "appref.dtd">
<appref>
<header>
<copyright>
<year>1997</year><year>2016</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
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.
</legalnotice>
<title>HiPE</title>
<prepared></prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date></date>
<rev></rev>
<file>hipe.xml</file>
</header>
<app>HiPE</app>
<appsummary>The HiPE Application</appsummary>
<description>
<p>
The normal way to native-compile an Erlang module using HiPE is to include the atom native
in the Erlang compiler options, as in:</p>
<pre>
1> <input>c(my_module, [native]).</input></pre>
<p>Options to the HiPE compiler are then passed as follows:</p>
<pre>
1> <input>c(my_module, [native,{hipe,Options}]).</input></pre>
<p>For on-line help in the Erlang shell, call <c>hipe:help()</c>.
Details on HiPE compiler options are given by <c>hipe:help_options()</c>.</p>
</description>
<section>
<title>Feature Limitations</title>
<p>
The HiPE compiler is in general compliant with the normal BEAM compiler,
with respect to semantic behavior. There are however features in the BEAM compiler
and the runtime system that have limited or no support for HiPE compiled modules.
</p>
<taglist>
<tag>Stack traces</tag>
<item><p>Stack traces returned from <seealso marker="erts:erlang#get_stacktrace/0">
<c>erlang:get_stacktrace/0</c></seealso> or as part of <c>'EXIT'</c> terms
can look incomplete if HiPE compiled functions are involved. Typically a stack trace
will contain only BEAM compiled functions or only HiPE compiled functions, depending
on where the exception was raised.</p>
<p>Source code line numbers in stack traces are also not supported by HiPE compiled functions.</p>
</item>
<tag>Tracing</tag>
<item><p>Erlang call trace is not supported by HiPE. Calling
<seealso marker="erts:erlang#trace_pattern/3"><c>erlang:trace_pattern({M,F,A}, ...)</c></seealso>
does not have any effect on HiPE compiled modules.</p>
</item>
<tag>NIFs</tag>
<item><p>Modules compiled with HiPE can not call <seealso marker="erts:erlang#load_nif-2">
<c>erlang:load_nif/2</c></seealso> to load NIFs.</p>
</item>
<tag>-on_load</tag>
<item><p>Modules compiled with HiPE can not use
<seealso marker="doc/reference_manual:code_loading#on_load"><c>-on_load()</c></seealso>
directives.</p>
</item>
</taglist>
</section>
<section>
<title>Performance Limitations</title>
<p>
The HiPE compiler does in general produce faster code than the
BEAM compiler. There are however some situation when HiPE
compiled code will perform worse than BEAM code.
</p>
<taglist>
<tag>Mode switches</tag>
<item><p>Every time a process changes from executing code in a
HiPE compiled module to a BEAM compiled module (or vice versa),
it will do a mode switch. This involves a certain amount of
CPU overhead which can have a negative net impact if the
process is switching back and forth without getting enough done in
each mode.</p>
</item>
<tag>Optimization for <c>receive</c> with unique references</tag>
<item>
<p>
The BEAM compiler can do an optimization when a receive
statement is only waiting for messages containing a reference
created before the receive. All messages that existed in the
queue when the reference was created will be bypassed, as they
cannot possibly contain the reference. HiPE currently has an
optimization similar this, but it is not guaranteed to
bypass all messages. In the worst case scenario it, cannot
bypass any messages at all.
</p>
<p>
An example of this is when <c>gen_server:call()</c> waits for
the reply message.
</p>
</item>
</taglist>
</section>
<section>
<title>Stability Issues</title>
<taglist>
<tag>Not yielding in <c>receive</c> statements</tag>
<item>
<p>HiPE will not yield in <c>receive</c> statements where
appropriate. If a process have lots of signals in its signal
queue and execute a HiPE compiled <c>receive</c> statement,
the scheduler thread performing the execution may be stuck
in the <c>receive</c> statement for a very long time. This
can in turn cause various severe issues such as for example
prevent the runtime system from being able to release
memory.
</p>
</item>
</taglist>
</section>
<section>
<title>SEE ALSO</title>
<p>
<seealso marker="stdlib:c">c(3)</seealso>,
<seealso marker="compiler:compile">compile(3)</seealso>
</p>
</section>
</appref>
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