GCC 6.1 发布，新增功能特性
发表于2016-04-28
GCC 6.1 发布了，该版本较之前GCC5 新怎了大量的功能特性，默认采用C++14为新的标准，替代了之前的C++98。OpenMP 4.5规范将在本版本中被支持。此外，GCC 6.1 增强了对 C++17 的试验性支持；大大改进了诊断特性，包括位置，位置范围，拼写错误标识符建议，选项名字等等改进；新增了修复提示和一些警告提示。
完整发布说明，可以在这里查看。C/C++ 语言主要改进记录如下：
一、C family
· Version 4.5 of the OpenMP specification is now supported in the C and C++ compilers.
· The C and C++ compilers now support attributes on enumerators. For instance, it is now possible to mark enumerators as deprecated:enum { newval, oldval __attribute__ ((deprecated ("too old")))};
· Source locations for the C and C++ compilers are now tracked as ranges, rather than just points, making it easier to identify the subexpression of interest within a complicated expression. For example:test.cc: In function 'int test(int, int, foo, int, int)': test.cc:5:16: error: no match for 'operator*' (operand types are 'int' and 'foo') return p + q * r * s + t; ~~^~~ In addition, there is now initial support for precise diagnostic locations within strings:format-strings.c:3:14: warning: field width specifier '*' expects a matching 'int' argument [-Wformat=] printf("%*d"); ^
· Diagnostics can now contain "fix-it hints", which are displayed in context underneath the relevant source code. For example:fixits.c: In function 'bad_deref': fixits.c:11:13: error: 'ptr' is a pointer; did you mean to use '->'? return ptr.x; ^ ->
· The C and C++ compilers now offer suggestions for misspelled field names:spellcheck-fields.cc:52:13: error: 'struct s' has no member named 'colour'; did you mean 'color'? return ptr->colour; ^~~~~~
· New command-line options have been added for the C and C++ compilers:
○ -Wshift-negative-value warns about left shifting a negative value.
○ -Wshift-overflow warns about left shift overflows. This warning is enabled by default. -Wshift-overflow=2 also warns about left-shifting 1 into the sign bit.
○ -Wtautological-compare warns if a self-comparison always evaluates to true or false. This warning is enabled by -Wall.
○ -Wnull-dereference warns if the compiler detects paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. This option is only active when -fdelete-null-pointer-checks is active, which is enabled by optimizations in most targets. The precision of the warnings depends on the optimization options used.
○ -Wduplicated-cond warns about duplicated conditions in an if-else-if chain.
○ -Wmisleading-indentation warns about places where the indentation of the code gives a misleading idea of the block structure of the code to a human reader. For example, given CVE-2014-1266:sslKeyExchange.c: In function 'SSLVerifySignedServerKeyExchange': sslKeyExchange.c:629:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation] if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0) ^~ sslKeyExchange.c:631:5: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if' goto fail; ^~~~ This warning is enabled by -Wall.
· The C and C++ compilers now emit saner error messages if merge-conflict markers are present in a source file.test.c:3:1: error: version control conflict marker in file <<<<<<< HEAD ^~~~~~~
二、C
· It is possible to disable warnings when an initialized field of a structure or a union with side effects is being overridden when using designated initializers via a new warning option -Woverride-init-side-effects.
· A new type attribute scalar_storage_order applying to structures and unions has been introduced. It specifies the storage order (aka endianness) in memory of scalar fields in structures or unions.
三、C++
· The default mode has been changed to -std=gnu++14.
· C++ Concepts are now supported when compiling with -fconcepts.
· -flifetime-dse is more aggressive in dead-store elimination in situations where a memory store to a location precedes a constructor to the memory location.
· G++ now supports C++17 fold expressions, u8 character literals, extended static_assert, and nested namespace definitions.
· G++ now allows constant evaluation for all non-type template arguments.
· G++ now supports C++ Transactional Memory when compiling with -fgnu-tm.
四、Runtime Library (libstdc++)
· Extensions to the C++ Library to support mathematical special functions (ISO/IEC 29124:2010), thanks to Edward Smith-Rowland.
· Experimental support for C++17, including the following new features:
○ std::uncaught_exceptions function (this is also available for -std=gnu++NN modes);
○ new member functions try_emplace and insert_or_assign for unique_key maps;
○ non-member functions std::size, std::empty, and std::data for accessing containers and arrays;
○ std::invoke;
○ std::shared_mutex;
○ std::void_t and std::bool_constant metaprogramming utilities.
Thanks to Ville Voutilainen for contributing many of the C++17 features.
· An experimental implementation of the File System TS.
· Experimental support for most features of the second version of the Library Fundamentals TS. This includes polymorphic memory resources and array support in shared_ptr, thanks to Fan You.
· Some assertions checked by Debug Mode can now also be enabled by _GLIBCXX_ASSERTIONS. The subset of checks enabled by the new macro have less run-time overhead than the full _GLIBCXX_DEBUG checks and don't affect the library ABI, so can be enabled per-translation unit.
· Timed mutex types are supported on more targets, including Darwin.
· Improved std::locale support for DragonFly and FreeBSD, thanks to John Marino and Andreas Tobler.
五、libgccjit
· The driver code is now run in-process within libgccjit, providing a small speed-up of the compilation process.
· The API has gained entrypoints for
○ timing how long was spent in different parts of code,
○ creating switch statements,
○ allowing unreachable basic blocks in a function, and
○ adding arbitrary command-line options to a compilation.