Hi,
this patch adds some info on changes in IPA and LTO. Not sure if I missed
something important. Martin, perhaps you could add some example on new
devirutalization stuff?
Suggestions for less lame explanations are welcome :)
Honza
Index: changes.html
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RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.7/changes.html,v
retrieving revision 1.28
diff -c -3 -r1.28 changes.html
*** changes.html 12 Sep 2011 07:46:05 -0000 1.28
--- changes.html 21 Sep 2011 09:51:12 -0000
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*** 58,63 ****
--- 58,122 ----
was added to allow users to control the cutoff between doing switch
statements
as a series of if statements and using a jump table.
</li>
+ <li>Link-time optimization improvements:
+ <ul>
+ <li>Improved scalability and reduced memory usage. Link time
optimization
+ of Firefox now require 3GB of RAM on 64bit system, while over 8GB was
needed
+ previously. Linking time has been improved, too. The serial stage of
linking
+ Firefox binary has been sped up approximately by factor of 10.</li>
+ <li>Reduced size of object files and temporary storage used during
linktime.</li>
+ <li>Streaming performance has been improved.</li>
+ <li>Number of bug fixes, especially in symbol table handling and
merging.</li>
+ </ul>
+ <li>Interprocedural optimization improvements:
+ <li>Inliner heuristic can now take into account fact that after inlining
+ code will be optimized out because of known values (or properties) of
function parameters.
+ For example:
+ <pre>
+ void foo(int a)
+ {
+ if (a>10)
+ ... huge code ...
+ }
+ void bar (void)
+ {
+ foo (0);
+ }
+ </pre>
+ The call of <code>foo</code> will be inlined into <code>bar</code> even
when
+ optimizing for code size. Constructs based on
<code>__builtin_constant_p</code>
+ are now understood by inliner and code size estimates are evaulated a
lot
+ more realistically.</li>
+ <li>Representation of C++ virtual thunks and aliases has been
+ re-engineered. The aliases no longer pose optimization barriers and
calls to an
+ alias can be inlined and otherwise optimized.</li>
+ <li>Inter-procedural constant propagation pass has been rewritten. It
now performs
+ generic function specialization. For example when compiling the
following:
+ <pre>
+ void foo(bool flag)
+ {
+ if (flag)
+ ... do something ...
+ else
+ ... do something else ...
+ }
+ void bar (void)
+ {
+ foo (false);
+ foo (true);
+ foo (false);
+ foo (true);
+ foo (false);
+ foo (true);
+ }
+ </pre>
+ GCC will now produce two copies of <code>foo</code>. One with
<code>flag</code> being
+ <code>true</code>, while other with <code>flag</code> being
+ <code>false</code>. This leads to preformance improvements previusly
+ possibly only by inlining all calls. Cloning cause a lot less code size
+ growth.
+ <ul>
+ </ul>
</ul>
<h2>New Languages and Language specific improvements</h2>
