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[WWWDOCS] Document IPA/LTO/FDO/i386 changes in GCC-4.9
- From: Jan Hubicka <hubicka at ucw dot cz>
- To: gcc-patches at gcc dot gnu dot org, gerald at pfeifer dot com
- Date: Mon, 18 Nov 2013 17:17:58 +0100
- Subject: [WWWDOCS] Document IPA/LTO/FDO/i386 changes in GCC-4.9
- Authentication-results: sourceware.org; auth=none
there was many changes in this area. The following are ones I can think of.
Please fell free to suggest more changes.
We probably should mention Teresa's splitting work once it is complete
and new micro-architectures targetd by x86 backend.
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.9/changes.html,v
retrieving revision 1.36
diff -u -r1.36 changes.html
--- changes.html 15 Nov 2013 15:40:00 -0000 1.36
+++ changes.html 18 Nov 2013 16:15:32 -0000
@@ -37,14 +37,52 @@
<li>AddressSanitizer, a fast memory error detector, is now available on ARM.
<li>UndefinedBehaviorSanitizer (ubsan), a fast undefined behavior detector,
has been added and can be enabled via <code>-fsanitize=undefined</code>.
Various computations will be instrumented to detect undefined behavior
at runtime. UndefinedBehaviorSanitizer is currently available for the C
and C++ languages.
+ <li>Link-time optimization (LTO) improvements:
+ <li>Type merging was rewritten. New implementation is significantly faster
+ and use less memory.
+ <li>Better partitioning algorithm resulting in less streaming during
+ <li>Early removal of virtual methods reduce size of object files and
+ improve link-time memory usage and compile time.</li>
+ <li>Functions are no longer pointlessly renamed.</li>
+ <li>Function bodies are now loaded on-demand and released early improving
+ overall memory usage at link-time.</li>
+ <li>C++ hidden keyed methods can now be optimized out.</li>
+ Memory usage of Firefox build with debug enabled was reduced from 15GB to
+ 3.5GB. Link time from 1700 seconds to 350 seconds.
+ <li>Inter-procedural optimization improvements:
+ <li>New type inheritance analysis module improving devirtualization.
+ Devirtualization now take into account anonymous name-spaces and the
+ C++11 <code>final</code> keyword.</li>
+ <li>New speculative devirtualization pass (controlled by
+ <li>Calls that was speculatively made direct are turned back to indirect
+ when doing so does not bring any noticeable benefits.</li>
+ <li>Local aliases are introduced for symbols that are known to be
+ semantically equivalent across shared libraries improving dynamic
+ linking times.</li>
+ <li>Feedback directed optimization improvements:
+ <li>Profiling of programs using C++ inline functions is now more reliable.</li>
+ <li>New time profiling determine typical order in which functions are executed.</li>
+ <li>New function reordering pass (controlled by
+ <code>-freorder-functions</code>) significantly reduces
+ startup time of large applications. Until binutils support is
+ completed, it is effective only with link time optimization.</li>
+ <li>Feedback driven indirect call removal and devirtualization now handle
+ cross-module calls when link-time optimization is enabled.</li>
<h2 id="languages">New Languages and Language specific improvements</h2>
@@ -325,9 +363,20 @@
- <li> GCC now supports the new Intel microarchitecture named Silvermont
+ <li>GCC now supports the new Intel microarchitecture named Silvermont
+ <li><code>-march=generic</code> has been retuned for better support of
+ Intel core and AMD Bulldozer architectures. Performance of AMD K7, K8,
+ Intel Pentium-M, and Pentium4 based CPUs is no longer considered important
+ for generic.
+ <li>Better inlining of <code>memcpy</code> and <code>memset</code>
+ that is avare of value ranges and produce shorter alignment prologues.
+ <li><code>-mno-accumulate-outgoing-args</code> is now honored when unwind
+ information is output. Argument accumulation is also now turned off
+ for portions of program optimized for size.</li>