This page is a "brief" summary of some of the huge number of improvementsin GCC 8.You may also want to check out ourPorting to GCC 8 page and thefull GCC documentation.
-std=gnu17 instead of-std=gnu11.-gcoff no longer does anything.std::atomic<void*> and types likestd::atomic<R(*)()> has been deprecated.std::copy_exception function was removed.std::make_exception_ptr should be used instead.Support for thepowerpc*-*-*spe* target ports which have been recently unmaintained and untested in GCC has been declared obsolete in GCC 8 asannounced. Unless there is activity to revive them, the next release of GCC will have their sources permanentlyremoved.
malloc attribute, and the corresponding warning option-Wsuggest-attribute=malloc emits a diagnostic for functions which can be annotated with themalloc attribute.cold attribute.Newly thenoreturn attribute does not imply all effects ofcold to differentiate betweenexit (whichisnoreturn) andabort (which is in additionnot executed in valid runs).-freorder-blocks-and-partition, a pass splitting functionbodies into hot and cold regions, is now enabled by default at-O2and higher for x86 and x86-64.-fcf-protection=[full|branch|return|none] is introduced to perform code instrumentation to increase program security by checking that target addresses of control-flow transfer instructions (such as indirect function call, function return, indirect jump) are valid. Currently the instrumentation is supported on x86 GNU/Linux targets only. See the user guide for further information about the option syntax and section "New Targets and Target Specific Improvements" for IA-32/x86-64 for more details.-gcolumn-info option is now enabled by default. It includes column information in addition to just filenames and line numbers in DWARF debugging information.-floop-nest-optimize has been overhauled. It's still considered experimental and may not result in any runtime improvements.-floop-unroll-and-jam performs outer loop unrolling and fusing of the inner loop copies.-floop-interchange exchanges loops in a loop nest to improve data locality. Both passes are enabled by default at-O3 and above.-ftree-loop-distribution has been improved and enabled by default at-O3 and above. It supports loop nest distribution in some restricted scenarios; it also supports cancellable innermost loop distribution with loop versioning under run-time alias checks.-fstack-clash-protection causes the compiler to insert probes whenever stack space is allocated statically or dynamically to reliably detect stack overflows and thus mitigate the attack vector that relies on jumping over a stack guard page as provided by the operating system.GCC unroll has been implemented in the C family of languages, as well as Fortran and Ada, so as to make it possible for the user to have a finer-grained control over the loop unrolling optimization.noreturn attribute on the second declaration below is mutually exclusive with themalloc attribute on the first, it is ignored and a warning is issued.> void* __attribute__ ((malloc)) f (unsigned); void* __attribute__ ((noreturn)) f (unsigned);warning:ignoring attribute 'noreturn' because it conflicts with attribute 'malloc' [-Wattributes]
gcov tool can distinguish functions that begin on a same line in a source file. This can be a different template instantiation or a class constructor:File 'ins.C'Lines executed:100.00% of 8Creating 'ins.C.gcov' -: 0:Source:ins.C -: 0:Graph:ins.gcno -: 0:Data:ins.gcda -: 0:Runs:1 -: 0:Programs:1 -: 1:template<class T> -: 2:class Foo -: 3:{ -: 4: public: 2: 5: Foo(): b (1000) {}------------------Foo<char>::Foo(): 1: 5: Foo(): b (1000) {}------------------Foo<int>::Foo(): 1: 5: Foo(): b (1000) {}------------------ 2: 6: void inc () { b++; }------------------Foo<char>::inc(): 1: 6: void inc () { b++; }------------------Foo<int>::inc(): 1: 6: void inc () { b++; }------------------ -: 7: -: 8: private: -: 9: int b; -: 10:}; -: 11: 1: 12:int main(int argc, char **argv) -: 13:{ 1: 14: Foo<int> a; 1: 15: Foo<char> b; -: 16: 1: 17: a.inc (); 1: 18: b.inc (); 1: 19:}gcov tool has more accurate numbers for execution of lines in a source file.gcov tool can use TERM colors to provide more readable output.-fsanitize=pointer-compare and-fsanitize=pointer-subtract, which warn about subtraction (or comparison) of pointers that point to a different memory object:intmain (){ /* Heap allocated memory. */ char *heap1 = (char *)__builtin_malloc (42); char *heap2 = (char *)__builtin_malloc (42); if (heap1 > heap2) return 1; return 0;}==17465==ERROR: AddressSanitizer: invalid-pointer-pair: 0x604000000010 0x604000000050 #0 0x40070f in main /tmp/pointer-compare.c:7 #1 0x7ffff6a72a86 in __libc_start_main (/lib64/libc.so.6+0x21a86) #2 0x400629 in _start (/tmp/a.out+0x400629)0x604000000010 is located 0 bytes inside of 42-byte region [0x604000000010,0x60400000003a)allocated by thread T0 here: #0 0x7ffff6efb390 in __interceptor_malloc ../../../../libsanitizer/asan/asan_malloc_linux.cc:86 #1 0x4006ea in main /tmp/pointer-compare.c:5 #2 0x7ffff6a72a86 in __libc_start_main (/lib64/libc.so.6+0x21a86)0x604000000050 is located 0 bytes inside of 42-byte region [0x604000000050,0x60400000007a)allocated by thread T0 here: #0 0x7ffff6efb390 in __interceptor_malloc ../../../../libsanitizer/asan/asan_malloc_linux.cc:86 #1 0x4006f8 in main /tmp/pointer-compare.c:6 #2 0x7ffff6a72a86 in __libc_start_main (/lib64/libc.so.6+0x21a86)SUMMARY: AddressSanitizer: invalid-pointer-pair /tmp/pointer-compare.c:7 in main-fsanitize=undefined:-fsanitize=builtin which diagnoses at run time invalid arguments to__builtin_clz or__builtin_ctz prefixed builtins, and-fsanitize=pointer-overflow which performs cheap run time tests for pointer wrapping.no_sanitize can be applied to functions to instruct the compiler not to do sanitization of the options provided as arguments to the attribute. Acceptable values forno_sanitize match those acceptable by the-fsanitize command-line option.void __attribute__ ((no_sanitize ("alignment", "object-size")))f () { /* Do something. */; }In this release cycle, the focus for the BRIGFE was on stabilization and performance improvements. Also a couple of completely new features were added.
-Wmultistatement-macros warns about unsafe macros expanding to multiple statements used as a body of a statement such asif,else,while,switch, orfor.-Wstringop-truncation warns for calls to bounded string manipulation functions such asstrncat,strncpy, andstpncpy that might either truncate the copied string or leave the destination unchanged. For example, the following call tostrncat is diagnosed because it appends just three of the four characters from the source string.void append (char *buf, size_t bufsize){ strncat (buf, ".txt", 3);}warning:'strncat' output truncated copying 3 bytes from a string of length 4 [-Wstringop-truncation] Similarly, in the following example, the call tostrncpy specifies the size of the destination buffer as the bound. If the length of the source string is equal to or greater than this size the result of the copy will not be NUL-terminated. Therefore, the call is also diagnosed. To avoid the warning, specifysizeof buf - 1 as the bound and set the last element of the buffer to NUL.void copy (const char *s){ char buf[80]; strncpy (buf, s, sizeof buf); …}warning:'strncpy' specified bound 80 equals destination size [-Wstringop-truncation] The-Wstringop-truncation option is included in-Wall.strncat,strncpy, orstpncpy as a macro in a system header as some implementations do, suppresses the warning.-Wif-not-aligned controls warnings issued in response to invalid uses of objects declared with attributewarn_if_not_aligned.-Wif-not-aligned option is included in-Wall.-Wmissing-attributes warns when a declaration of a function is missing one or more attributes that a related function is declared with and whose absence may adversely affect the correctness or efficiency of generated code. For example, in C++, the warning is issued when an explicit specialization of a primary template declared with attributealloc_align,alloc_size,assume_aligned,format,format_arg,malloc, ornonnull is declared without it. Attributesdeprecated,error, andwarning suppress the warning.-Wmissing-attributes option is included in-Wall.-Wpacked-not-aligned warns when astruct orunion declared with attributepacked defines a member with an explicitly specified alignment greater than 1. Such a member will wind up under-aligned. For example, a warning will be issued for the definition ofstruct A in the following:struct __attribute__ ((aligned (8)))S8 { char a[8]; };struct __attribute__ ((packed)) A{ struct S8 s8;};warning:alignment 1 of 'struct S' is less than 8 [-Wpacked-not-aligned] The-Wpacked-not-aligned option is included in-Wall.-Wcast-function-type warns when a function pointeris cast to an incompatible function pointer. This warning is enabledby-Wextra.-Wsizeof-pointer-div warns for suspicious divisionsof the size of a pointer by the size of the elements it points to,which looks like the usual way to compute the array size butwon't work out correctly with pointers.This warning is enabled by-Wall.-Wcast-align=strict warns whenever a pointer is castsuch that the required alignment of the target is increased. Forexample, warn if achar * is cast to anint *regardless of the target machine.-fprofile-abs-path creates absolute path names in the.gcno files. This allowsgcov to find thecorrect sources in projects where compilations occur with differentworking directories.-fno-strict-overflow is now mapped to-fwrapv -fwrapv-pointer and signed integer overflow is now undefined by default at all optimization levels. Using-fsanitize=signed-integer-overflow is now the preferred way to audit code,-Wstrict-overflow is deprecated.-Warray-bounds option has been improved to detect more instances of out-of-bounds array indices and pointer offsets. For example, negative or excessive indices into flexible array members and string literals are detected.-Wrestrict option introduced in GCC 7 has been enhanced to detect many more instances of overlapping accesses to objects viarestrict-qualified arguments to standard memory and string manipulation functions such asmemcpy andstrcpy. For example, thestrcpy call in the function below attempts to truncate the string by replacing its initial characters with the last four. However, because the function writes the terminating NUL intoa[4], the copies overlap and the call is diagnosed.void f (void){ char a[] = "abcd1234"; strcpy (a, a + 4); …}warning:'strcpy' accessing 5 bytes at offsets 0 and 4 overlaps 1 byte at offset 4 [-Wrestrict] The-Wrestrict option is included in-Wall.-Wformat-overflow and-Wformat-truncation options. The warnings detect more instances of buffer overflow and truncation than in GCC 7 and are better at avoiding certain kinds of false positives.$ gcc arg-type-mismatch.ccarg-type-mismatch.cc: In function 'int caller(int, int, float)':arg-type-mismatch.cc:5:24:error:invalid conversion from 'int' to 'const char*' [-fpermissive] return callee(first,second, third);^~~~~~arg-type-mismatch.cc:1:40:note: initializing argument 2 of 'int callee(int, const char*, float)' extern int callee(int one,const char *two, float three);~~~~~~~~~~~~^~~
#include directives for various headers in the C and C++ standard libraries.$ gcc incomplete.cincomplete.c: In function 'test':incomplete.c:3:10:error:'NULL' undeclared (first use in this function) returnNULL;^~~~incomplete.c:3:10:note:'NULL' is defined in header '<stddef.h>'; did you forget to '#include <stddef.h>'?incomplete.c:1:1:+#include <stddef.h> const char *test(void)incomplete.c:3:10: returnNULL;^~~~incomplete.c:3:10:note:each undeclared identifier is reported only once for each function it appears in
$ gcc incomplete.ccincomplete.cc:1:6:error:'string' in namespace 'std' does not name a type std::string s("hello world");^~~~~~incomplete.cc:1:1:note:'std::string' is defined in header '<string>'; did you forget to '#include <string>'?+#include <string>std::string s("hello world");^~~
$ gcc t.ct.c: In function 'test':t.c:3:12:error:expected ';' before '}' token return 42^;}~
$ gcc unclosed.cunclosed.c: In function 'log_when_out_of_range':unclosed.c:12:50:error:expected ')' before '{' token && (temperature < MIN || temperature > MAX){^~)unclosed.c:11:6:note:to match this '(' if(logging_enabled && check_range ()^or highlighting it directly if it's on the same line:
$ gcc unclosed-2.cunclosed-2.c: In function 'test':unclosed-2.c:8:45:error:expected ')' before '{' token if(temperature < MIN || temperature > MAX{~^~)They will also emit fix-it hints.
-std=c17, to select support for the 2018 edition of the ISO C standard (__STDC_VERSION__ == 201710L), and-std=gnu17, for C17 with GNU extensions.-std=gnu17.-fabi-version=12) has a couple of corrections to the calling convention, which changes the ABI for some uncommon code:-fabi-version=13).-Wabi=11 (or-Wabi=12 in GCC 8.2 for the third issue); if these changes are problematic for your project, the GCC 7 ABI can be selected with-fabi-version=11.alignof operator has been corrected to match C_Alignof (minimum alignment) rather than GNU__alignof__ (preferred alignment); on ia32 targets this means thatalignof(double) is now 4 rather than 8. Code that wants the preferred alignment should use__alignof__ instead.-Wclass-memaccess warns when objects of non-trivial class types are manipulated in potentially unsafe ways by raw memory functions such asmemcpy, orrealloc. The warning helps detect calls that bypass user-defined constructors or copy-assignment operators, corrupt virtual table pointers, data members ofconst-qualified types or references, or member pointers. The warning also detects calls that would bypass access controls to data members. For example, a call such as:memcpy (&std::cout, &std::cerr, sizeof std::cout);results in
warning:'void* memcpy(void*, const void*, long unsigned int)' writing to an object of type 'std::ostream' {aka'class std::basic_ostream<char>'} with no trivial copy-assignment [-Wclass-memaccess]The
-Wclass-memaccess option is included in-Wall.-std=c++2a or-std=gnu++2a flags, including designated initializers, default member initializers for bit-fields,__VA_OPT__ (except that#__VA_OPT__ is unsupported), lambda[=, this] captures, etc. For a full list of new features, seethe C++ status page.$ gcc accessor.ccaccessor.cc: In function 'void test(foo*)':accessor.cc:12:12:error:'double foo::m_ratio' is private within this context if (ptr->m_ratio >= 0.5)^~~~~~~accessor.cc:7:10:note:declared private here doublem_ratio;^~~~~~~accessor.cc:12:12:note:field 'double foo::m_ratio' can be accessed via 'double foo::get_ratio() const' if (ptr->m_ratio >= 0.5)^~~~~~~get_ratio()
#include directives):$ gcc ordering.ccordering.cc:2:24:error:expected ';' at end of member declaration virtual void clone()const OVERRIDE { }^~~~~;ordering.cc:2:30:error:'OVERRIDE' does not name a type virtual void clone() constOVERRIDE { }^~~~~~~~ordering.cc:2:30:note:the macro 'OVERRIDE' had not yet been definedIn file included fromordering.cc:5:c++11-compat.h:2:note:it was later defined here #define OVERRIDE override
-Wold-style-cast diagnostic can now emit fix-it hints telling you when you can use astatic_cast,const_cast, orreinterpret_cast.$ gcc -c old-style-cast-fixits.cc -Wold-style-castold-style-cast-fixits.cc: In function 'void test(void*)':old-style-cast-fixits.cc:5:19:warning:use of old-style cast to 'struct foo*' [-Wold-style-cast] foo *f = (foo *)ptr;^~~----------static_cast<foo *> (ptr)
extern "C" linkage specifications, the C++ compiler will now display the location of the start of theextern "C".$ gcc -c extern-c.ccextern-c.cc:3:1:error:template with C linkagetemplate <typename T> void test (void);^~~~~~~~In file included fromextern-c.cc:1:unclosed.h:1:1:note:'extern "C"' linkage started hereextern "C" {^~~~~~~~~~extern-c.cc:3:39:error:expected '}' at end of input template <typename T> void test (void);^In file included fromextern-c.cc:1:unclosed.h:1:12:note:to match this '{' extern "C"{^
[...] instead:$ gcc templates.cctemplates.cc: In function 'void test()':templates.cc:9:8:error:could not convert 'vector<double>()' from 'vector<double>' to 'vector<int>' fn_1(vector<double> ());^~~~~~~~~~~~~~~~~templates.cc:10:8:error:could not convert 'map<int, double>()' from 'map<[...],double>' to 'map<[...],int>' fn_2(map<int, double>());^~~~~~~~~~~~~~~~~~Those
[...] elided parameters can be seen using-fno-elide-type:$ gcc templates.cc -fno-elide-typetemplates.cc: In function 'void test()':templates.cc:9:8:error:could not convert 'vector<double>()' from 'vector<double>' to 'vector<int>' fn_1(vector<double> ());^~~~~~~~~~~~~~~~~templates.cc:10:8:error:could not convert 'map<int, double>()' from 'map<int,double>' to 'map<int,int>' fn_2(map<int, double>());^~~~~~~~~~~~~~~~~~The C++ compiler has also gained an option
-fdiagnostics-show-template-tree which visualizes such mismatching templates in a hierarchical form:$ gcc templates-2.cc -fdiagnostics-show-template-treetemplates-2.cc: In function 'void test()':templates-2.cc:9:8:error:could not convert 'vector<double>()' from 'vector<double>' to 'vector<int>' vector< [double !=int]> fn_1(vector<double> ());^~~~~~~~~~~~~~~~~templates-2.cc:10:8:error:could not convert 'map<map<int, vector<double> >, vector<double> >()' from 'map<map<[...],vector<double>>,vector<double>>' to 'map<map<[...],vector<float>>,vector<float>>' map< map< [...], vector< [double !=float]>>, vector< [double !=float]>> fn_2(map<map<int, vector<double>>, vector<double>> ());^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~which again works with
-fno-elide-type:$ gcc templates-2.cc -fdiagnostics-show-template-tree -fno-elide-typetemplates-2.cc: In function 'void test()':templates-2.cc:9:8:error:could not convert 'vector<double>()' from 'vector<double>' to 'vector<int>' vector< [double !=int]> fn_1(vector<double> ());^~~~~~~~~~~~~~~~~templates-2.cc:10:8:error:could not convert 'map<map<int, vector<double> >, vector<double> >()' from 'map<map<int,vector<double>>,vector<double>>' to 'map<map<int,vector<float>>,vector<float>>' map< map< int, vector< [double !=float]>>, vector< [double !=float]>> fn_2(map<map<int, vector<double>>, vector<double>> ());^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Wreturn-type warnings are enabled by default for C++.std::filesystem implementation.std::char_traits<char> andstd::char_traits<wchar_t> are usable in constant expressions.std::to_chars andstd::from_chars (for integers only, not for floating point types).std::to_address (thanks to Glen Fernandes) andstd::endian.std::random_device::entropy() accesses the kernel's entropy count for the random device, if known (thanks to Xi Ruoyao).std::experimental::source_location.std::vector, detecting out-of-range accesses to the unused capacity of a vector.__gnu_cxx::airy_ai and__gnu_cxx::airy_bi added to the Mathematical Special Functions.-fc-prototypes to write C prototypes forBIND(C) procedures and variables.-fmax-stack-var-size is honored if given together with-Ofast,-fstack-arrays is no longer set in that case.-fdefault-real-16 and-fdefault-real-10 to control the default kind ofREAL variables.-Wdo-subscript, enabled by-Wextra, warns about this even if the compiler can not prove that the code will be executed.FORALL andDO CONCURRENT statements with multiple indices. This behavior be controlled with the new flag-ffrontend-loop-interchange, which is enabled with optimization by default. The-Wfrontend-loop-interchange option warns about such occurrences.-std=legacy option can be used to still compile such code.RECL= argument toOPEN andINQUIRE statements now allows 64-bit integers, making records larger than 2GiB possible.GFORTRAN_DEFAULT_RECL environment variable no longer has any effect. The record length for preconnected units is now larger than any practical limit, same as for sequential access units opened without an explicitRECL= specifier.HUGE(0) elements are now possible on 64-bit targets. Note that this changes the procedure call ABI for all procedures with character arguments on 64-bit targets, as the type of the hidden character length argument has changed. The hidden character length argument is now of typeINTEGER(C_SIZE_T).The libgccjit API gained four new entry points:
The C code generated bygcc_jit_context_dump_reproducer_to_fileis now easier-to-read.
-march=armv8.4-a option.+dotprod architecture extension. E.g.-march=armv8.2-a+dotprod.+crypto extension has now been split into two extensions for finer grained control:+aes which contains the Armv8-A AES crytographic instructions.+sha2 which contains the Armv8-A SHA2 and SHA1 cryptographic instructions.+crypto will now enable these two extensions.+fp16fml architectural extension on Armv8.2-A and Armv8.3-A. On Armv8.4-A the instructions can be enabled by specifying+fp16.+sha3 New SHA3 and SHA2 instructions from Armv8.4-A. This implies+sha2.+sm4 New SM3 and SM4 instructions from Armv8.4-A.+sve architecture extension (for example,-march=armv8.2-a+sve). By default, the generated code works with all vector lengths, but it can be made specific toN-bit vectors using-msve-vector-bits=N.cortex-a75).cortex-a55).cortex-a75.cortex-a55).-mcpu or-mtune options, for example:-mcpu=cortex-a75 or-mtune=cortex-a75 or as arguments to the equivalent target attributes and pragmas.aux variable attributes.uncached type qualifier.sjli instruction.-G command-line option.-mrf16 command-line option.-mlpc-width command-line option to control the width of thelp_count register.-mfpu option now takes a new option setting of-mfpu=auto. When set to this the floating-point and SIMD settings are derived from the settings of the-mcpu or-march options. The internal CPU configurations have been updated with information about the permitted floating-point configurations supported. See the user guide for further information about the extended option syntax for controlling architectural extensions via the-march option.-mfpu=auto is now the default setting unless the compiler has been configured with an explicit--with-fpu option.-march and-mcpu options now accept optional extensions to the architecture or CPU option, allowing the user to enable or disable any such extensions supported by that architecture or CPU such as (but not limited to) floating-point and AdvancedSIMD. For example: the option-mcpu=cortex-a53+nofp will generate code for the Cortex-A53 processor with no floating-point support. This, in combination with the new-mfpu=auto option, provides a straightforward way of specifying a valid build target through a single-mcpu or-march option. The-mtune option accepts the same arguments as-mcpu but only the CPU name has an effect on tuning. The architecture extensions do not have any effect. For details of what extensions a particular architecture or CPU option supports please refer to thedocumentation.-mstructure-size-boundary option has been deprecated and will be removed in a future release.-mbe32 can be used to force the linker to produce legacy BE32 format images. There is no change of behavior for Armv6-M and other Armv7 or later targets: these already defaulted to BE8 format. This change brings GCC into alignment with other compilers for the ARM architecture.-march=armv8-r option.-march=armv8.3-a option.-march=armv8.4-a option.+dotprod architecture extension. E.g.-march=armv8.2-a+dotprod.#pragma GCC target ("arch=..."),#pragma GCC target ("+extension"),__attribute__((target("arch=..."))) or__attribute__((target("+extension"))).+fp16fml architectural extension on Armv8.2-A and Armv8.3-A. On Armv8.4-A the instructions can be enabled by specifying+fp16.cortex-a75).cortex-a55).cortex-a75.cortex-a55).cortex-r52).-mcpu or-mtune options, for example:-mcpu=cortex-a75 or-mtune=cortex-r52 or as arguments to the equivalent target attributes and pragmas.ATtiny212, ATtiny214, ATtiny412, ATtiny414, ATtiny416, ATtiny417, ATtiny814, ATtiny816, ATtiny817, ATtiny1614, ATtiny1616, ATtiny1617, ATtiny3214, ATtiny3216, ATtiny3217The new devices are listed under
-mmcu=avrxmega3.PROGMEM and__flashare not needed any more (as opposed to other AVR families for whichread-only data will be located in RAM except special, non-standardfeatures are used to locate and access such data). This requiresthat the compiler is used with Binutils 2.29 or newer so thatread-only data will be located in flash memory.-mshort-calls is supported.This option is used internally for multilib selection of theavrxmega3 variants. It isnot an optimization option. Do not set it by hand.__gcc_isr which is supported and resolved by the GNU assembler.__gcc_isr pseudo-instruction will be resolved bythe assembler, inline assembly is transparent to the process.This means that when inline assembly uses an instruction likeINC that clobbers the condition code,then the assembler will detect this and generate an appropriateISR prologue / epilogue chunk to save / restore SREG as needed.-mno-gas-isr-prologuesdisables the generation of the__gcc_isr pseudoinstruction. Any non-naked ISR will save and restoreSREG,tmp_reg andzero_reg, no matterwhether the respective register is clobbered or used.-O0 and-Og. It is explicitlyenabled by means of option-mgas-isr-prologues.no_gccisr. It can be usedto disable__gcc_isr pseudo instruction generationfor individual ISRs.main; the effect is the same as if attributeOS_task was specified formain. This optimization can be switched off by the new command-line option-mno-main-is-OS_task.naked function attribute.znver1 and Intel Core based CPUs.-march=cannonlake. The switch enables the AVX512VBMI, AVX512IFMA and SHA ISA extensions.-march=icelake. The switch enables the AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ ISA extensions.-fcf-protection option.-mext-perf,-mext-perf2, and-mext-string have been added for performance extension instructions.-mgprel-sec= and-mr0rel-sec= have been added.powerpcspe port. The separate port is deprecated and might be removed in a future release.-mpaired,powerpc*-*-linux*paired*) is deprecated and will be removed in a future release.-mxilinx-fpu,powerpc-xilinx-eabi*) is deprecated and will be removed in a future release.-maltivec=be) is deprecated and will be removed in a future release.--enable-mingw-wildcard or--disable-mingw-wildcard to force a specific behavior for GCC itself with regards to supporting the wildcard character. Prior versions of GCC would follow the configuration of the MinGW runtime. This behavior can still be obtained by not using the above options or by using--enable-mingw-wildcard=platform.break-on-diagnostic command, providing an easy way to trigger a breakpoint whenever a diagnostic is emitted.This is thelistof problem reports (PRs) from GCC's bug tracking system that areknown to be fixed in the 8.1 release. This list might not becomplete (that is, it is possible that some PRs that have been fixedare not listed here).
This is thelistof problem reports (PRs) from GCC's bug tracking system that areknown to be fixed in the 8.2 release. This list might not becomplete (that is, it is possible that some PRs that have been fixedare not listed here).
-fabi-version=13 and makes it the default, ABI incompatibilities between GCC 8.1 and 8.2 can be reported with-Wabi=12. SeeC++ changes for more details.-mtune=native performance regressionPR84413 on Intel Skylake processors has been fixed.This is thelistof problem reports (PRs) from GCC's bug tracking system that areknown to be fixed in the 8.3 release. This list might not becomplete (that is, it is possible that some PRs that have been fixedare not listed here).
-mms-bitfields option is specified, or__attribute__((ms_struct)) is used-mhitachi option is specified, or__attribute__((renesas)) is usedThis is thelistof problem reports (PRs) from GCC's bug tracking system that areknown to be fixed in the 8.4 release. This list might not becomplete (that is, it is possible that some PRs that have been fixedare not listed here).
This is thelistof problem reports (PRs) from GCC's bug tracking system that areknown to be fixed in the 8.5 release. This list might not becomplete (that is, it is possible that some PRs that have been fixedare not listed here).
-moutline-atomics has been added to aid deployment of the Large System Extensions (LSE) on GNU/Linux systems built with a baseline architecture targeting Armv8-A. When the option is specified code is emitted to detect the presence of LSE instructions at run time and use them for standard atomic operations. For more information please refer to the documentation.Copyright (C)Free Software Foundation, Inc.Verbatim copying and distribution of this entire article ispermitted in any medium, provided this notice is preserved.
These pages aremaintained by the GCC team.Last modified 2025-01-31.