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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>Modules compiled with HiPE have very limited support for runtime tracing
using <seealso marker="erts:erlang#trace_pattern/3"><c>erlang:trace_pattern/3</c></seealso>.</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 <c>receive</c> statement is <em>only</em> 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
does not implement this optimization.</p>
<p>An example of this is when
<c>gen_server:call()</c> waits for the reply message.</p>
</item>
<tag>Unused list comprehensions</tag>
<item><p>List comprehensions used only for their side effects,
will be optimized by BEAM to not produce the unused result
list. This optimization is not done by HiPE.</p>
<pre>
_ = [io:format("~p~n",[N]) || N <- lists:seq(1,10)],</pre>
</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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