Hi,
it seems I have updated the patch for comments received but did not send
updated version to the ML. Here it is.
Honza
Index: changes.html
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of array bounds. In particular, it enables
<code>-fsanitize=bounds</code> as well as instrumentation of
flexible array member-like arrays.</li>
+ <li>Type-based alias analysis now disambiguates accesses to different
+ pointers. This improves precision of the alias oracle by about 20-30%
+ on higher-level C++ programs. Programs doing invalid type punning
+ of pointer types may now need <code>-fno-strict-aliasing</code>
+ to work correctly.</li>
+ <li>Alias analysis now correctly supports <code>weakref</code> and
+ <code>alias</code> attributes. This makes it possible to access
+ both a variable and its alias in one translation unit which is common
+ with link-time optimization.</li>
+ <li>Value range propagation now assumes that <code>this</code> pointer
+ of C++ member functions is non-<code>NULL</code>. This eliminates
+ common <code>NULL</code> pointer checks
+ but also breaks some non-conforming code-bases (such as Qt-5, Chromium,
+ KDevelop). As a temporary work-around
+ <code>-fno-delete-null-pointer-checks</code> can be used. Wrong
+ code can be identified by using <code>-fsanitize=undefined</code>.</li>
+ <li>Link-time optimization improvements:
+ <ul>
+ <li><code>warning</code> and <code>error</code> attributes are now
+ correctly preserved by declaration linking and thus
+ <code>-D_FORTIFY_SOURCE=2</code> is now supported with
<code>-flto</code>.</li>
+ <li><p>Type merging was fixed to handle C and Fortran interoperability
+ rules as defined by the Fortran 2008 language standard.</p>
+ <p>
+ As an exception, <code>CHARACTER(KIND=C_CHAR)</code> is not
inter-operable
+ with <code>char</code> in all cases because it is an array while
+ <code>char</code> is scalar.
+ <code>INTEGER(KIND=C_SIGNED_CHAR)</code> should be used instead.
+ In general, this inter-operability can not be implemented, for
+ example, on targets where function passing conventions of arrays
+ differs from scalars.</p>
+ <li>More type information is now preserved at link time reducing
+ the loss of accuracy of the type based alias analysis compared
+ to builds without link-time optimization.</li>
+ <li>Invalid type punning on global variables and declarations is now
+ reported with <code>-Wodr-type-mismatch</code>.</li>
+ <li>The size of LTO object files was reduced by about 11% (measured
+ by compiling Firefox 46.0).</li>
+ <li>Link-time parallelization (enabled using <code>-flto=n</code>)
+ was significantly improved by decreasing the size of streamed
+ data when partitioning programs. The size of streamed
+ IL while compiling Firefox 46.0 was reduced by 66%.</li>
+ <li><p>Linker plugin was extended to pass information about type of
+ binary produced to GCC back-end (that can be also manually controlled
+ by <code>-flinker-output</code>). This makes it possible to
+ properly confiugre code generator and support incremental
+ linking. Incremental linking of LTO objects by <code>gcc -r</code> is
+ now supported on plugin-enabled setups.</p>
+ <p>There are two ways to perform incremental linking:
+ <ol>
+ <li>Linking by <code>ld -r</code> will result in object file
+ with all sections from individual object files mechanically merged.
+ This delays the actual linking to the time final binary is produced
+ and thus permits whole program optimization. Linking such object
+ file is however slower.
+ <li>Linking by <code>gcc -r</code> will lead to link time
optimization
+ and produce final binary into the object file. Linking such object
+ file is fast but avoids any benefirts from whole program
optimization.</li>
+ </ol>
+ GCC 7 will support incremental link-time optimization with <code>gcc
-r</code>.
+ </ul></li>
+ <li>Inter-procedural optimization improvements:
+ <ul>
+ <li>Basic jump threading is now performed before profile construction
+ and inline analysis, resulting in more realistic size and time
estimates
+ that drive the heuristics of the of inliner and function cloning
passes.</li>
+ <li>Function cloning now more aggressively eliminates unused function
+ parameters.</li>
+ </ul></li>
</ul>
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