Hi,
this patch adds list of changes to IPA/LTO/FDO before I forget about them ;)
Honza
Index: changes.html
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RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-5/changes.html,v
retrieving revision 1.9
diff -c -p -r1.9 changes.html
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<h2 id="general">General Optimizer Improvements</h2>
<ul>
+ <li>Inter-procedural optimization improvements:
+ <ul>
+ <li>Devirtualization pass was significantly improved by adding
+ better support for speculative devirtualization and dynamic type
+ detection. About 50% of virtual calls in Firefox are speculatively
+ devirtualized during link-time optimization.
+ <li>New comdat localization pass lets linker to eliminate more dead code
+ in presence of C++ inline functions.</li>
+ <li>Virtual tables are now optimized. Local aliases are used to reduce
+ dynamic linking time of C++ virtual tables on ELF targets and
+ data alignment has been reduced to limit data segment bloat.</li>
+ <li>New <code>-fno-semantic-interposition</code> flag can be used
+ to improve code quality of shared libraries where interposition of
+ exported symbols is not allowed.</li>
+ <li>Write-only variables are now detected and optimized out.</li>
+ <li>With profile feedback the function inliner can now bypass
+ <code>--param inline-insns-auto</code> and <code>--param
+ inline-insns-single</code> limits for hot calls.</li>
+ <li>IPA reference pass was significantly sped up making it feasible
+ to enable <code>-fipa-reference</code> with
+ <code>-fprofile-generage</code>. This also solve bottleneck
+ seen when optimizing Chromium with link time optimization.</li>
+ <li>Symbol table and call-graph API was reworked to C++ and
+ simplified.</li>
+ </ul></li>
+ <li>Link-time optimization improvements:
+ <ul>
+ <li>New One Definition Rule based merging of C++ types implemented.
+ Type merging enables better devirtualization and alias analysis.
+ Streaming extra information needed to merge types adds about 2-6% of
+ memory size and object size increase. This can be controlled by
+ <code>-flto-odr-type-merging</code>.</li>
+ <li>GCC bootstrap now use slim LTO object files.</li>
+ <li>Memory usage and link times was improved. Tree merging was sped up,
+ memory usage of GIMPLE declarations and types was reduced, and,
+ support for on-demand streaming of variable constructors was
added.</li>
+ </ul></li>
+ <li>Feedback directed optimization improvements:
+ <ul>
+ <li>Profile precision was improved in presence of C++ inline and extern
+ inline functions.</li>
+ <li>New <code>gcov-tool</code> to manipulate profiles.</li>
+ <li>Profile is now more tolerant to source file changes (this can be
+ controlled by <code>--param profile-func-internal-id</code>).</li>
+ </ul></li>
<li>UndefinedBehaviorSanitizer gained a few new sanitization options:
<ul>
<li><code>-fsanitize=float-divide-by-zero</code>: detect floating-point
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*** 54,59 ****
--- 99,107 ----
<li>Full support for <a href="https://www.cilkplus.org/";>Cilk Plus</a>
has been added to the GCC compiler. Cilk Plus is an extension to
the C and C++ languages to support data and task parallelism.</li>
+ <li>New attribute <code>no_reorder</code> prevents reordering of selected
symbols.
+ This enables to link-time optimize Linux kernel without need to use
+ <code>-fno-toplevel-reorder</code> that disable several
optimizations.</li>
</ul>
<h3 id="c">C</h3>
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*** 90,95 ****
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<li>An implementation of <code>std::experimental::any</code>.</li>
<li>New random number distributions <code>logistic_distribution</code> and
<code>uniform_on_sphere_distribution</code> as extensions.</li>
+ <li>New One Definition Rule violation warning (controlled by
<code>-Wodr</code)
+ detects mismatches in type definitions and virtual table contents
+ during link-time optimization.</li>
+ <li>New warnings <code>-Wsuggest-final-types</code> and
+ <code>-Wsuggest-final-methods</code> helps developers
+ to annotate programs by <code>final</code> specifiers (or anonymous
+ namespaces) in the cases where code generation improves.
+ These warnings can be used at compile time, but they are more
+ useful in combination with link-time optimization.</li>
</ul>
<h3 id="fortran">Fortran</h3>
