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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 19. Profile Mode</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" C++ , library , profile "/><meta name="keywords" content=" ISO C++ , library "/><meta name="keywords" content=" ISO C++ , runtime , library "/><link rel="home" href="../index.html" title="The GNU C++ Library"/><link rel="up" href="extensions.html" title="Part III. Extensions"/><link rel="prev" href="bk01pt03ch18s05.html" title="Testing"/><link rel="next" href="bk01pt03ch19s02.html" title="Design"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 19. Profile Mode</th></tr><tr><td align="left"><a accesskey="p" href="bk01pt03ch18s05.html">Prev</a> </td><th width="60%" align="center">Part III.
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Extensions
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</th><td align="right"> <a accesskey="n" href="bk01pt03ch19s02.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 19. Profile Mode"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.profile_mode"/>Chapter 19. Profile Mode</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.intro">Intro</a></span></dt><dd><dl><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.using">Using the Profile Mode</a></span></dt><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.tuning">Tuning the Profile Mode</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s02.html">Design</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.wrapper">Wrapper Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.instrumentation">Instrumentation</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.rtlib">Run Time Behavior</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.analysis">Analysis and Diagnostics</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.cost-model">Cost Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.reports">Reports</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.testing">Testing</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s03.html">Extensions for Custom Containers</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s04.html">Empirical Cost Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html">Implementation Issues</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.stack">Stack Traces</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.symbols">Symbolization of Instruction Addresses</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.concurrency">Concurrency</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.stdlib-in-proflib">Using the Standard Library in the Instrumentation Implementation</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.malloc-hooks">Malloc Hooks</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.construction-destruction">Construction and Destruction of Global Objects</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s06.html">Developer Information</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s06.html#manual.ext.profile_mode.developer.bigpic">Big Picture</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s06.html#manual.ext.profile_mode.developer.howto">How To Add A Diagnostic</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s07.html">Diagnostics</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.template">Diagnostic Template</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.containers">Containers</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.hashtable_too_small">Hashtable Too Small</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.hashtable_too_large">Hashtable Too Large</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.inefficient_hash">Ineffi
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<span class="emphasis"><em>Goal: </em></span>Give performance improvement advice based on
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recognition of suboptimal usage patterns of the standard library.
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</p><p>
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<span class="emphasis"><em>Method: </em></span>Wrap the standard library code. Insert
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calls to an instrumentation library to record the internal state of
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various components at interesting entry/exit points to/from the standard
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library. Process trace, recognize suboptimal patterns, give advice.
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For details, see
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<a class="link" href="http://dx.doi.org/10.1109/CGO.2009.36">paper presented at
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CGO 2009</a>.
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</p><p>
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<span class="emphasis"><em>Strengths: </em></span>
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</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
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Unintrusive solution. The application code does not require any
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modification.
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</p></li><li class="listitem"><p> The advice is call context sensitive, thus capable of
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identifying precisely interesting dynamic performance behavior.
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</p></li><li class="listitem"><p>
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The overhead model is pay-per-view. When you turn off a diagnostic class
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at compile time, its overhead disappears.
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</p></li></ul></div><p>
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</p><p>
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<span class="emphasis"><em>Drawbacks: </em></span>
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</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
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You must recompile the application code with custom options.
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</p></li><li class="listitem"><p>You must run the application on representative input.
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The advice is input dependent.
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</p></li><li class="listitem"><p>
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The execution time will increase, in some cases by factors.
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</p></li></ul></div><p>
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</p><div class="section" title="Using the Profile Mode"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.using"/>Using the Profile Mode</h3></div></div></div><p>
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This is the anticipated common workflow for program <code class="code">foo.cc</code>:
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</p><pre class="programlisting">
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$ cat foo.cc
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#include <vector>
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int main() {
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vector<int> v;
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for (int k = 0; k < 1024; ++k) v.insert(v.begin(), k);
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}
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$ g++ -D_GLIBCXX_PROFILE foo.cc
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$ ./a.out
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$ cat libstdcxx-profile.txt
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vector-to-list: improvement = 5: call stack = 0x804842c ...
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: advice = change std::vector to std::list
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vector-size: improvement = 3: call stack = 0x804842c ...
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: advice = change initial container size from 0 to 1024
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</pre><p>
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</p><p>
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Anatomy of a warning:
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</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
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Warning id. This is a short descriptive string for the class
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that this warning belongs to. E.g., "vector-to-list".
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</p></li><li class="listitem"><p>
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Estimated improvement. This is an approximation of the benefit expected
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from implementing the change suggested by the warning. It is given on
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a log10 scale. Negative values mean that the alternative would actually
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do worse than the current choice.
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In the example above, 5 comes from the fact that the overhead of
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inserting at the beginning of a vector vs. a list is around 1024 * 1024 / 2,
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which is around 10e5. The improvement from setting the initial size to
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1024 is in the range of 10e3, since the overhead of dynamic resizing is
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linear in this case.
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</p></li><li class="listitem"><p>
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Call stack. Currently, the addresses are printed without
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symbol name or code location attribution.
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Users are expected to postprocess the output using, for instance, addr2line.
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</p></li><li class="listitem"><p>
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The warning message. For some warnings, this is static text, e.g.,
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"change vector to list". For other warnings, such as the one above,
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the message contains numeric advice, e.g., the suggested initial size
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of the vector.
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</p></li></ul></div><p>
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</p><p>Three files are generated. <code class="code">libstdcxx-profile.txt</code>
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contains human readable advice. <code class="code">libstdcxx-profile.raw</code>
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contains implementation specific data about each diagnostic.
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Their format is not documented. They are sufficient to generate
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all the advice given in <code class="code">libstdcxx-profile.txt</code>. The advantage
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of keeping this raw format is that traces from multiple executions can
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be aggregated simply by concatenating the raw traces. We intend to
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offer an external utility program that can issue advice from a trace.
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<code class="code">libstdcxx-profile.conf.out</code> lists the actual diagnostic
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parameters used. To alter parameters, edit this file and rename it to
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<code class="code">libstdcxx-profile.conf</code>.
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</p><p>Advice is given regardless whether the transformation is valid.
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For instance, we advise changing a map to an unordered_map even if the
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application semantics require that data be ordered.
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We believe such warnings can help users understand the performance
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behavior of their application better, which can lead to changes
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at a higher abstraction level.
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</p></div><div class="section" title="Tuning the Profile Mode"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.tuning"/>Tuning the Profile Mode</h3></div></div></div><p>Compile time switches and environment variables (see also file
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profiler.h). Unless specified otherwise, they can be set at compile time
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using -D_<name> or by setting variable <name>
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in the environment where the program is run, before starting execution.
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</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
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<code class="code">_GLIBCXX_PROFILE_NO_<diagnostic></code>:
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disable specific diagnostics.
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See section Diagnostics for possible values.
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(Environment variables not supported.)
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</p></li><li class="listitem"><p>
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<code class="code">_GLIBCXX_PROFILE_TRACE_PATH_ROOT</code>: set an alternative root
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path for the output files.
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</p></li><li class="listitem"><p>_GLIBCXX_PROFILE_MAX_WARN_COUNT: set it to the maximum
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number of warnings desired. The default value is 10.</p></li><li class="listitem"><p>
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<code class="code">_GLIBCXX_PROFILE_MAX_STACK_DEPTH</code>: if set to 0,
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the advice will
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be collected and reported for the program as a whole, and not for each
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call context.
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This could also be used in continuous regression tests, where you
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just need to know whether there is a regression or not.
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The default value is 32.
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</p></li><li class="listitem"><p>
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<code class="code">_GLIBCXX_PROFILE_MEM_PER_DIAGNOSTIC</code>:
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set a limit on how much memory to use for the accounting tables for each
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diagnostic type. When this limit is reached, new events are ignored
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until the memory usage decreases under the limit. Generally, this means
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that newly created containers will not be instrumented until some
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live containers are deleted. The default is 128 MB.
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</p></li><li class="listitem"><p>
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<code class="code">_GLIBCXX_PROFILE_NO_THREADS</code>:
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Make the library not use threads. If thread local storage (TLS) is not
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available, you will get a preprocessor error asking you to set
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-D_GLIBCXX_PROFILE_NO_THREADS if your program is single-threaded.
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Multithreaded execution without TLS is not supported.
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(Environment variable not supported.)
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</p></li><li class="listitem"><p>
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<code class="code">_GLIBCXX_HAVE_EXECINFO_H</code>:
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This name should be defined automatically at library configuration time.
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If your library was configured without <code class="code">execinfo.h</code>, but
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you have it in your include path, you can define it explicitly. Without
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it, advice is collected for the program as a whole, and not for each
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call context.
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(Environment variable not supported.)
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</p></li></ul></div><p>
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</p></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h2 class="title"><a id="profile_mode.biblio"/>Bibliography</h2></div></div></div><div class="biblioentry"><a id="id514403"/><p><span class="citetitle"><em class="citetitle">
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Perflint: A Context Sensitive Performance Advisor for C++ Programs
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</em>. </span><span class="author"><span class="firstname">Lixia</span> <span class="surname">Liu</span>. </span><span class="author"><span class="firstname">Silvius</span> <span class="surname">Rus</span>. </span><span class="copyright">Copyright © 2009 . </span><span class="publisher"><span class="publishername">
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Proceedings of the 2009 International Symposium on Code Generation
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and Optimization
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. </span></span></p></div></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="bk01pt03ch18s05.html">Prev</a> </td><td align="center"><a accesskey="u" href="extensions.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch19s02.html">Next</a></td></tr><tr><td align="left" valign="top">Testing </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Design</td></tr></table></div></body></html>
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