This page is a "brief" summary of some of the huge number of improvements in GCC 8. You may also want to check out our Porting to GCC 8 page and the full GCC documentation.
-gcoff no longer
      does anything.std::atomic<void*>
    and types like std::atomic<R(*)()>
    has been deprecated.std::copy_exception function was
    removed. std::make_exception_ptr should be used instead.
  Support for the powerpc*-*-*spe* target ports which have
    been recently unmaintained and untested in GCC has been declared
    obsolete in GCC 8 as announced
    here.
    Unless there is activity to revive them, the
    next release of GCC will have their sources permanently
    removed.
malloc attribute, and the corresponding warning option
      -Wsuggest-attribute=malloc emits a diagnostic for
      functions which can be annotated with the malloc
      attribute.cold attribute.
	Newly the noreturn attribute does not imply all effects of
	cold to differentiate between exit (which
	is noreturn) and abort (which is in addition
	not executed in valid runs).-freorder-blocks-and-partition, a pass splitting function
	bodies into hot and cold regions, is now enabled by default at -O2
	and 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 the malloc
    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 8
Creating '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:
  
int
main ()
{
  /* 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.
  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 as if, else,
	  while, switch, or for.-Wstringop-truncation
	  warns for calls to bounded string manipulation functions such as
	  strncat, strncpy, and stpncpy
	  that might either truncate the copied string or leave the destination
	  unchanged.  For example, the following call to strncat
	  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 to strncpy
	  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, specify
	  sizeof 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,
	  or stpncpy 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 attribute
	  warn_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 attribute
	  alloc_align, alloc_size,
	  assume_aligned, format,
	  format_arg, malloc, or nonnull
	  is declared without it. Attributes deprecated,
	  error, and warning suppress the warning.
	  -Wmissing-attributes option is included in
	  -Wall.-Wpacked-not-aligned warns
	  when a struct or union declared with
	  attribute packed 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 of struct 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 pointer
	is cast to an incompatible function pointer.  This warning is enabled
	by -Wextra.-Wsizeof-pointer-div warns for suspicious divisions
	of 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 but
	won't work out correctly with pointers.
	This warning is enabled by -Wall.-Wcast-align=strict warns whenever a pointer is cast
	such that the required alignment of the target is increased.  For
	example, warn if a char * is cast to an int *
	regardless of the target machine.-fprofile-abs-path creates absolute path names in the
	.gcno files.  This allows gcov to find the
	correct sources in projects where compilations occur with different
	working 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 via restrict-qualified arguments to
      standard memory and string manipulation functions such as
      memcpy and strcpy.  For example,
      the strcpy 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 into
      a[4], the copies overlap and the call is diagnosed.
	void f (void)
	{
	    char a[] = "abcd1234";
	    strcpy (a, a + 4);
	    …
	}
      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.cc arg-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.c incomplete.c: In function 'test': incomplete.c:3:10: error: 'NULL' undeclared (first use in this function) return NULL; ^~~~ 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: return NULL; ^~~~ incomplete.c:3:10: note: each undeclared identifier is reported only once for each function it appears in
$ gcc incomplete.cc incomplete.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.c t.c: In function 'test': t.c:3:12: error: expected ';' before '}' token return 42 ^ ; } ~
$ gcc unclosed.c unclosed.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.c unclosed-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.
alignof operator has been corrected
    to match C _Alignof (minimum alignment) rather than
    GNU __alignof__ (preferred alignment); on ia32 targets this
    means that alignof(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 as memcpy, or
      realloc.  The warning helps detect calls that bypass
      user-defined constructors or copy-assignment operators, corrupt
      virtual table pointers, data members of const-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,
    see the C++
    status page.
  $ gcc accessor.cc accessor.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 double m_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.cc ordering.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() const OVERRIDE { } ^~~~~~~~ ordering.cc:2:30: note: the macro 'OVERRIDE' had not yet been defined In file included from ordering.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 a static_cast,
    const_cast, or reinterpret_cast.
$ gcc -c old-style-cast-fixits.cc -Wold-style-cast old-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 the extern "C".
$ gcc -c extern-c.cc extern-c.cc:3:1: error: template with C linkage template <typename T> void test (void); ^~~~~~~~ In file included from extern-c.cc:1: unclosed.h:1:1: note: 'extern "C"' linkage started here extern "C" { ^~~~~~~~~~ extern-c.cc:3:39: error: expected '}' at end of input template <typename T> void test (void); ^ In file included from extern-c.cc:1: unclosed.h:1:12: note: to match this '{' extern "C" { ^
[...] instead:
$ gcc templates.cc templates.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-type templates.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-tree templates-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-type templates-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> and
        std::char_traits<wchar_t> are usable in constant
        expressions.std::to_chars and std::from_chars (for
      integers only, not for floating point types).std::to_address (thanks to Glen Fernandes)
    and std::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 for
    BIND(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 of REAL variables.
  -Wdo-subscript,
    enabled by -Wextra, warns about this even if the compiler can
    not prove that the code will be executed.
  FORALL and DO
    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 to OPEN
    and INQUIRE 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 explicit RECL= 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 type INTEGER(C_SIZE_T).
  The libgccjit API gained four new entry points:
The C code generated by gcc_jit_context_dump_reproducer_to_file is 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 to N-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 lp_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 the
    documentation.
  -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 __flash
	are not needed any more (as opposed to other AVR families for which
	read-only data will be located in RAM except special, non-standard
	features are used to locate and access such data). This requires
	that the compiler is used with Binutils 2.29 or newer so that
	read-only data will be
	  located in flash memory.-mshort-calls is supported.
	This option is used internally for multilib selection of the
	avrxmega3 variants. It is
	not 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 by
	the assembler, inline assembly is transparent to the process.
	This means that when inline assembly uses an instruction like
	INC that clobbers the condition code,
	then the assembler will detect this and generate an appropriate
	ISR prologue / epilogue chunk to save / restore SREG as needed.-mno-gas-isr-prologues
	disables the generation of the __gcc_isr pseudo
	instruction. Any non-naked ISR will save and restore SREG,
	tmp_reg and zero_reg, no matter
	whether the respective register is clobbered or used.-O0 and -Og. It is explicitly
	enabled by means of option -mgas-isr-prologues.no_gccisr. It can be used
	to disable __gcc_isr pseudo instruction generation
	for individual ISRs.main;
    the effect is the same as if attribute OS_task was
    specified for main.  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.-mibt, -mshstk,
    -mcet options. One of these options has to accompany the
    -fcf-protection option to enable code instrumentation for
    control-flow protection. 
  -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.
  Copyright (C) Free Software Foundation, Inc. Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.
These pages are maintained by the GCC team. Last modified 2018-04-27.