<table><tr><td style="">dfaure requested changes to this revision.<br />dfaure added inline comments.
</td><a style="text-decoration: none; padding: 4px 8px; margin: 0 8px 8px; float: right; color: #464C5C; font-weight: bold; border-radius: 3px; background-color: #F7F7F9; background-image: linear-gradient(to bottom,#fff,#f1f0f1); display: inline-block; border: 1px solid rgba(71,87,120,.2);" href="https://phabricator.kde.org/D26126">View Revision</a></tr></table><br /><div><strong>INLINE COMMENTS</strong><div><div style="margin: 6px 0 12px 0;"><div style="border: 1px solid #C7CCD9; border-radius: 3px;"><div style="padding: 0; background: #F7F7F7; border-color: #e3e4e8; border-style: solid; border-width: 0 0 1px 0; margin: 0;"><div style="color: #74777d; background: #eff2f4; padding: 6px 8px; overflow: hidden;"><a style="float: right; text-decoration: none;" href="https://phabricator.kde.org/D26126#inline-147537">View Inline</a><span style="color: #4b4d51; font-weight: bold;">kconfig_compiler.cpp:1020</span></div>
<div style="font: 11px/15px "Menlo", "Consolas", "Monaco", monospace; white-space: pre-wrap; clear: both; padding: 4px 0; margin: 0;"><div style="padding: 0 8px; margin: 0 4px; background: rgba(251, 175, 175, .7);"> <span class="bright"></span><span class="p"><span class="bright">}</span></span><span class="bright"> </span><span style="color: #aa4000"><span class="bright">else</span></span><span class="bright"> </span><span style="color: #aa4000"><span class="bright">if</span></span><span class="bright"> </span><span class="p"><span class="bright">(</span></span><span class="bright"></span><span class="n"><span class="bright">type</span></span><span class="bright"> </span><span style="color: #aa2211"><span class="bright">==</span></span> <span class="n">QLatin1String</span><span class="p">(</span><span style="color: #766510">"<span class="bright">font"</span></span><span class="bright"></span><span class="p"><span class="bright">))</span></span><span class="bright"> </span><span class="p"><span class="bright">{</span></span>
</div><div style="padding: 0 8px; margin: 0 4px; background: rgba(251, 175, 175, .7);"> <span class="bright"></span><span style="color: #aa4000"><span class="bright">return</span></span><span class="bright"> </span><span class="n"><span class="bright">QStringLiteral</span></span><span class="bright"></span><span class="p"><span class="bright">(</span></span><span class="bright"></span><span style="color: #766510"><span class="bright">"const QFont &"</span></span><span class="bright"></span><span class="p"><span class="bright">);</span></span>
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</div><div style="padding: 0 8px; margin: 0 4px; background: rgba(151, 234, 151, .6);"> <span class="bright"> </span> <span class="n">QLatin1String</span><span class="p">(</span><span style="color: #766510">"<span class="bright">double"</span></span><span class="bright"></span><span class="p"><span class="bright">)}</span></span>
</div><div style="padding: 0 8px; margin: 0 4px; background: rgba(151, 234, 151, .6);"> <span class="bright"></span><span class="p"><span class="bright">).</span></span><span class="bright"></span><span class="n"><span class="bright">contains</span></span><span class="bright"></span><span class="p"><span class="bright">(</span></span><span class="bright"></span><span class="n"><span class="bright">type</span></span><span class="bright"></span><span class="p"><span class="bright">))</span></span><span class="bright"> </span><span class="p"><span class="bright">{</span></span>
</div><div style="padding: 0 8px; margin: 0 4px; background: rgba(151, 234, 151, .6);"> <span class="bright"> </span><span style="color: #aa4000"><span class="bright">return</span></span><span class="bright"> </span><span class="n"><span class="bright">type</span></span><span class="bright"></span><span class="p"><span class="bright">;</span></span>
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<div style="margin: 8px 0; padding: 0 12px;"><p style="padding: 0; margin: 8px;">This linear search doesn't look like an optimization to me. It would be better to incorporate this into the map, so that a single search is performed, rather than two.</p></div></div><br /><div style="border: 1px solid #C7CCD9; border-radius: 3px;"><div style="padding: 0; background: #F7F7F7; border-color: #e3e4e8; border-style: solid; border-width: 0 0 1px 0; margin: 0;"><div style="color: #74777d; background: #eff2f4; padding: 6px 8px; overflow: hidden;"><a style="float: right; text-decoration: none;" href="https://phabricator.kde.org/D26126#inline-147473">View Inline</a><span style="color: #4b4d51; font-weight: bold;">ervin</span> wrote in <span style="color: #4b4d51; font-weight: bold;">kconfig_compiler.cpp:1024</span></div>
<div style="margin: 8px 0; padding: 0 12px; color: #74777D;"><p style="padding: 0; margin: 8px;">std::map looks like a bad idea here, either use QHash (preferred in massively based Qt code) or std::unordered_map.</p>
<p style="padding: 0; margin: 8px;">Also for both temporaries you pay the price of their allocation and deallocation at each call. Even a mutex used at each call would do better. ;-)</p></div></div>
<div style="margin: 8px 0; padding: 0 12px;"><p style="padding: 0; margin: 8px;">I'm not 100% sure about std::map vs QHash given the number of elements, this would need benchmarking.</p>
<p style="padding: 0; margin: 8px;">But I agree 100% that compiler-generated thread safety around a static is NOTHING compared to amount of nodes allocated to fill in a map or hash.</p>
<p style="padding: 0; margin: 8px;"><a href="https://phabricator.kde.org/p/tcanabrava/" style="
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padding: 0 4px;">@tcanabrava</a> Please have a look at <a href="https://gist.github.com/jboner/2841832" class="remarkup-link" target="_blank" rel="noreferrer">https://gist.github.com/jboner/2841832</a><br />
Locking an available mutex is 4 times faster than even fetching data from main memory (i.e. data which isn't yet in a CPU cache). This is many orders of magnitude faster than creating a filling a map or a hash full of QStrings. On top of that, compilers don't even generate a full-blown mutex for threadsafe statics, they generate a three-state atomic (a bit like Q_GLOBAL_STATIC does) (3 because not created, being created, already created).</p>
<p style="padding: 0; margin: 8px;">The most performant solution is to turn the input string into a QByteArray and then perform a binary search in a C array of const char* (no allocations, even the very first time).<br />
The most readable (but still good, unlike the current code in git) solution is a static map.</p></div></div></div></div></div><br /><div><strong>REPOSITORY</strong><div><div>R237 KConfig</div></div></div><br /><div><strong>REVISION DETAIL</strong><div><a href="https://phabricator.kde.org/D26126">https://phabricator.kde.org/D26126</a></div></div><br /><div><strong>To: </strong>tcanabrava, ervin, dfaure<br /><strong>Cc: </strong>dfaure, ervin, GB_2, apol, kde-frameworks-devel, LeGast00n, michaelh, ngraham, bruns<br /></div>