Hi!
The following patch attempts to document in similar style to last years
new C++23/26 papers and DRs implemented in GCC 15 (for
the papers I've used https://gcc.gnu.org/projects/cxx-status.html
as source, for DRs skimmed gcc-cvs commits with /DRs/ and left out those
that just committed a testcase for something that was already working),
C2Y papers (again, scanned gcc-cvs, dunno if I've handled everything)
and for C23 just mentioned #embed, unsequenced/reproduceable and
__STDC_VERSION__ bump.
Martin's aliasing/type compatibility changes are missing (dunno how to
word those) and we need to document that C switched to -std=gnu23 by
default.
In addition to that I went through all my r15- commits and tried to
find user visible stuff that should be documented (left out
__builtin_operator_{new,delete} as I think that is meant to be used
primarily just in libstdc++ headers).
Ok for wwwdocs?
--- a/htdocs/gcc-15/changes.html
+++ b/htdocs/gcc-15/changes.html
@@ -32,6 +32,13 @@ a work-in-progress.</p>
<li>Support for Nios II targets, which was marked obsolete in GCC 14,
has now been removed entirely.
</li>
+ <li><code>{0}</code> initializer in C or C++ for unions no longer
+ guarantees clearing of the whole union (except for static storage
+ duration initialization), it just initializes the first
+ union member to zero. If initialization of the whole union including
+ padding bits is desirable, use <code>{}</code> (valid in C23 or C++)
+ or use <code>-fzero-init-padding-bits=unions</code> option to restore
+ old GCC behavior.</li>
</ul>
@@ -92,13 +99,153 @@ a work-in-progress.</p>
<h3 id="c-family">C family</h3>
<ul>
- <li>A <a
href="https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#index-musttail-statement-attribute";>
- <code>musttail</code> statement attribute</a> was added to enforce
tail calls.</li>
+ <li>A <a
href="https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#index-musttail-statement-attribute";>
+ <code>musttail</code> statement attribute</a> was added to enforce
tail calls.</li>
+ <li><a
href="https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html";>Extended</a> inline
assembler statements
+ can now be used with some limitations outside of functions as well, new
+ constraints have been for defining symbols or using symbols inside of
inline
+ assembler and a new generic operand modifier has been added to allow
+ printing those regardless of PIC. For example:
+<pre>
+struct S { int a, b, c; };
+extern foo (void);
+extern char var;
+int var2;
+asm (".text; %cc0: mov %cc2, %%r0; .previous;"
+ ".rodata: %cc1: .byte %3; .previous" : :
+ ":" (foo), /* Tell compiler asm defines foo function. */
+ ":" (&var), /* Tell compiler asm defines var variable. */
+ "-s" (var2), /* Tell compiler asm uses var2 variable. */
+ /* "s" would work too but might not work with -fpic. */
+ "i" (sizeof (struct S))); /* It is possible to pass constants to toplevel
asm. */
+</pre>
+ </li>
+ <li>The <code>"redzone"</code> clobber is now allowed in inline
+ assembler statements to describe that the assembler can overwrite
+ memory in the stack red zone (e.g. on x86-64 or PowerPC).</li>
+ <li>The <a
href="https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-nonnull_005fif_005fnonzero-function-attribute";>
+ nonnull_if_nonzero</a> function attribute has been added to describe
+ functions where some pointer parameter may be <code>NULL</code> only
+ if some other parameter is zero.</li>
+ <li>The <a
href="https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wtrailing-whitespace_003d";>
+ <code>-Wtrailing-whitespace=</code></a> and
+ <a
href="https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wleading-whitespace_003d";>
+ <code>-Wleading-whitespace=</code></a> options have been added to
+ diagnose certain whitespace characters at the end of source lines or
+ whitespace characters at the start of source lines violating certain
+ indentation styles.</li>
+ <li>The <a
href="https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wheader-guard";>
+ <code>-Wheader-guard</code></a> warning has been added and enabled
+ in <code>-Wall</code> to warn about some inconsistencies in header
+ file guarding macros.</li>
+</ul>
+
+<h3 id="c">C</h3>
+
+<ul>
+ <li>Some more C23 features have been implemented:
+ <ul>
+ <li><code>#embed</code> preprocessing directive support
+ (as an extension enabled in C++ as well).</li>
+ <li>Support for <code>unsequenced</code> and <code>reproducible</code>
+ attributes.</li>
+ <li><code>__STDC_VERSION__</code> predefined macro value changed
+ for <code>-std=c23</code> or <code>-std=gnu23</code> to
+ <code>202311L</code>.</li>
+ </ul>
+ </li>
+ <li>Some new features from the upcoming C2Y revision of the ISO C
+ standard are supported with <code>-std=c2y</code>
+ and <code>-std=gnu2y</code>. Some of these features are also
+ supported as extensions when compiling for older language versions.
+ <ul>
+ <li>Generic selection expression with a type operand.</li>
+ <li>Support <code>++</code> and <code>--</code> on complex values.</li>
+ <li>Accessing byte arrays.</li>
+ <li><code>alignof</code> of an incomplete array type.</li>
+ <li>Obsolete implicitly octal literals and add delimited escape
+ sequences (just partially implemented, support for new syntax added
+ but nothing deprecated yet).</li>
+ <li>Named loops.</li>
+ <li>More Modern Bit Utilities (addition of
+ <code>__builtin_stdc_rotate_left</code> and
+ <code>__builtin_stdc_rotate_right</code> builtins for use in future
+ C library <code><stdbit.h></code> headers).</li>
+ <li>Case range expressions.</li>
+ <li><code>if</code> declarations.</li>
+ <li>Introduce complex literals.</li>
+ <li>Abs Without Undefined Behavior (addition of builtins for
+ use in future C library <code><stdlib.h></code> headers).</li>
+ </ul>
+ </li>
</ul>
<h3 id="cxx">C++</h3>
<ul>
+ <li>Several C++26 features have been implemented:
+ <ul>
+ <li><a href="https://wg21.link/P2558R2";>P2558R2</a>, Add @, $, and ` to
the basic
+ character set (<a href="https://gcc.gnu.org/PR110343";>PR110343</a>)
+ </li>
+ <li><a href="https://wg21.link/P2662R3";>P2662R3</a>, Pack indexing
+ (<a href="https://gcc.gnu.org/PR113798";>PR113798</a>)
+ </li>
+ <li><a href="https://wg21.link/P0609R3";>P0609R3</a>, Attributes for
structured
+ bindings (<a href="https://gcc.gnu.org/PR114456";>PR114456</a>)
+ </li>
+ <li><a href="https://wg21.link/P2573R2";>P2573R2</a>,
+ <code>= delete("reason");</code> (<a
href="https://gcc.gnu.org/PR114458";>PR114458</a>)
+ </li>
+ <li><a href="https://wg21.link/P2893R3";>P2893R3</a>, Variadic friends
+ (<a href="https://gcc.gnu.org/PR114459";>PR114459</a>)
+ </li>
+ <li><a href="https://wg21.link/P3034R1";>P3034R1</a>, Disallow module
declarations
+ to be macros (<a href="https://gcc.gnu.org/PR114461";>PR114461</a>)
+ </li>
+ <li><a href="https://wg21.link/P2747R2";>P2747R2</a>,
<code>constexpr</code>
+ placement new (<a href="https://gcc.gnu.org/PR115744";>PR115744</a>)
+ </li>
+ <li><a href="https://wg21.link/P0963R3";>P0963R3</a>, Structured binding
declaration
+ as a condition (<a href="https://gcc.gnu.org/PR115745";>PR115745</a>)
+ </li>
+ <li><a href="https://wg21.link/P3144R2";>P3144R2</a>, Deleting a pointer
to an
+ incomplete type should be ill-formed
+ (<a href="https://gcc.gnu.org/PR115747";>PR115747</a>)
+ </li>
+ <li><a href="https://wg21.link/P3176R0";>P3176R0</a>, Oxford variadic
comma
+ (<a href="https://gcc.gnu.org/PR117786";>PR117786</a>)
+ </li>
+ <li><a href="https://wg21.link/P2865R5";>P2865R5</a>, Removing deprecated
array
+ comparisons (<a href="https://gcc.gnu.org/PR117788";>PR117788</a>)
+ </li>
+ </ul>
+ </li>
+ <li>Several C++23 features have been implemented:
+ <ul>
+ <li><a href="https://wg21.link/P2615R1";>P2615R1</a>, Meaningful exports
+ (<a href="https://gcc.gnu.org/PR107688";>PR107688</a>)
+ </li>
+ <li><a href="https://wg21.link/P2718R0";>P2718R0</a>, Wording for P2644R1
+ Fix for Range-based for Loop
+ (<a href="https://gcc.gnu.org/PR107637";>PR107637</a>)
+ </li>
+ </ul>
+ </li>
+ <li>Several C++ Defect Reports have been resolved, e.g.:
+ <ul>
+ <li><a href="https://wg21.link/cwg882";>DR 882</a>,
+ Defining main as deleted</li>
+ <li><a href="https://wg21.link/cwg2387";>DR 2387</a>,
+ Linkage of const-qualified variable template</li>
+ <li><a href="https://wg21.link/cwg2521";>DR 2521</a>,
+ User-defined literals and reserved identifiers</li>
+ <li><a href="https://wg21.link/cwg2627";>DR 2627</a>,
+ Bit-fields and narrowing conversions</li>
+ <li><a href="https://wg21.link/cwg2918";>DR 2918</a>,
+ Consideration of constraints for address of overloaded function</li>
+ </ul>
+ </li>
<li>Inline assembler statements now support
<a
href="https://gcc.gnu.org/onlinedocs/gcc/asm-constexprs.html";><code>constexpr</code>
generated strings</a>,
analoguous to <code>static_assert</code>.</li>
@@ -108,6 +255,14 @@ a work-in-progress.</p>
<code>this->non_existent</code>, is now proactively diagnosed
when parsing a template.
</li>
+ <li>The <a
href="https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-fassume-sane-operators-new-delete";>
+ <code>-fassume-sane-operators-new-delete</code></a> option has been
+ added and enabled by default. This option allows control over some
+ optimizations around calls to replaceable global operators new and
+ delete. If a program overrides those replaceable global operators and
+ the replaced definitions read or modify global state visible to the
+ rest of the program, programs might need to be compiled with
+ <code>-fno-assume-sane-operators-new-delete</code>.
</ul>
<h4 id="libstdcxx">Runtime Library (libstdc++)</h4>
@@ -149,6 +304,10 @@ a work-in-progress.</p>
longer permitted by default and are rejected at run-time unless
-std=legacy
is used when compiling the main program unit. See Fortran 2023
constraint C1302.
</li>
+ <li>The Fortran module <code>*.mod</code> format generated by GCC 15 is
+ incompatible with the module format generated by GCC 8 - 14, but GCC
+ 15 can for compatibility still read GCC 8 - 14 created module
+ files.</li>
</ul>
<!-- <h3 id="go">Go</h3> -->
Jakub
