* Long Long:: Double-word integers---@code{long long int}.
* Complex:: Data types for complex numbers.
* Floating Types:: Additional Floating Types.
+* Half-Precision:: Half-Precision Floating Point.
* Decimal Float:: Decimal Floating Types.
* Hex Floats:: Hexadecimal floating-point constants.
* Fixed-Point:: Fixed-Point Types.
@end smallexample
Not all targets support additional floating point types. @code{__float80}
-is supported on i386, x86_64 and ia64 targets and target @code{__float128}
-is supported on x86_64 and ia64 targets.
+and @code{__float128} types are supported on i386, x86_64 and ia64 targets.
+
+@node Half-Precision
+@section Half-Precision Floating Point
+@cindex half-precision floating point
+@cindex @code{__fp16} data type
+
+On ARM targets, GCC supports half-precision (16-bit) floating point via
+the @code{__fp16} type. You must enable this type explicitly
+with the @option{-mfp16-format} command-line option in order to use it.
+
+ARM supports two incompatible representations for half-precision
+floating-point values. You must choose one of the representations and
+use it consistently in your program.
+
+Specifying @option{-mfp16-format=ieee} selects the IEEE 754-2008 format.
+This format can represent normalized values in the range of @math{2^{-14}} to 65504.
+There are 11 bits of significand precision, approximately 3
+decimal digits.
+
+Specifying @option{-mfp16-format=alternative} selects the ARM
+alternative format. This representation is similar to the IEEE
+format, but does not support infinities or NaNs. Instead, the range
+of exponents is extended, so that this format can represent normalized
+values in the range of @math{2^{-14}} to 131008.
+
+The @code{__fp16} type is a storage format only. For purposes
+of arithmetic and other operations, @code{__fp16} values in C or C++
+expressions are automatically promoted to @code{float}. In addition,
+you cannot declare a function with a return value or parameters
+of type @code{__fp16}.
+
+Note that conversions from @code{double} to @code{__fp16}
+involve an intermediate conversion to @code{float}. Because
+of rounding, this can sometimes produce a different result than a
+direct conversion.
+
+ARM provides hardware support for conversions between
+@code{__fp16} and @code{float} values
+as an extension to VFP and NEON (Advanced SIMD). GCC generates
+code using the instructions provided by this extension if you compile
+with the options @option{-mfpu=neon-fp16 -mfloat-abi=softfp},
+in addition to the @option{-mfp16-format} option to select
+a half-precision format.
+
+Language-level support for the @code{__fp16} data type is
+independent of whether GCC generates code using hardware floating-point
+instructions. In cases where hardware support is not specified, GCC
+implements conversions between @code{__fp16} and @code{float} values
+as library calls.
@node Decimal Float
@section Decimal Floating Types
@itemize @bullet
@item
-Pragma @code{FLOAT_CONST_DECIMAL64} is not supported, nor is the @samp{d}
-suffix for literal constants of type @code{double}.
-
-@item
When the value of a decimal floating type cannot be represented in the
integer type to which it is being converted, the result is undefined
rather than the result value specified by the draft technical report.
These attributes are not currently implemented for Objective-C@.
@item deprecated
+@itemx deprecated (@var{msg})
@cindex @code{deprecated} attribute.
The @code{deprecated} attribute results in a warning if the function
is used anywhere in the source file. This is useful when identifying
int (*fn_ptr)() = old_fn;
@end smallexample
-results in a warning on line 3 but not line 2.
+results in a warning on line 3 but not line 2. The optional msg
+argument, which must be a string, will be printed in the warning if
+present.
The @code{deprecated} attribute can also be used for variables and
types (@pxref{Variable Attributes}, @pxref{Type Attributes}.)
+@item disinterrupt
+@cindex @code{disinterrupt} attribute
+On MeP targets, this attribute causes the compiler to emit
+instructions to disable interrupts for the duration of the given
+function.
+
@item dllexport
@cindex @code{__declspec(dllexport)}
On Microsoft Windows targets and Symbian OS targets the
another affect---it can cause the vtable and run-time type information
for a class to be exported. This happens when the class has a
dllimport'ed constructor or a non-inline, non-pure virtual function
-and, for either of those two conditions, the class also has a inline
+and, for either of those two conditions, the class also has an inline
constructor or destructor and has a key function that is defined in
the current translation unit.
instead of using @code{rts}. The board-specific return routine simulates
the @code{rtc}.
+On MeP targets this causes the compiler to use a calling convention
+which assumes the called function is too far away for the built-in
+addressing modes.
+
@item fastcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{fastcall} attribute causes the compiler to
@item interrupt
@cindex interrupt handler functions
-Use this attribute on the ARM, AVR, CRX, M32C, M32R/D, m68k,
+Use this attribute on the ARM, AVR, CRX, M32C, M32R/D, m68k, MeP, MIPS
and Xstormy16 ports to indicate that the specified function is an
interrupt handler. The compiler will generate function entry and exit
sequences suitable for use in an interrupt handler when this attribute
On ARMv7-M the interrupt type is ignored, and the attribute means the function
may be called with a word aligned stack pointer.
+On MIPS targets, you can use the following attributes to modify the behavior
+of an interrupt handler:
+@table @code
+@item use_shadow_register_set
+@cindex @code{use_shadow_register_set} attribute
+Assume that the handler uses a shadow register set, instead of
+the main general-purpose registers.
+
+@item keep_interrupts_masked
+@cindex @code{keep_interrupts_masked} attribute
+Keep interrupts masked for the whole function. Without this attribute,
+GCC tries to reenable interrupts for as much of the function as it can.
+
+@item use_debug_exception_return
+@cindex @code{use_debug_exception_return} attribute
+Return using the @code{deret} instruction. Interrupt handlers that don't
+have this attribute return using @code{eret} instead.
+@end table
+
+You can use any combination of these attributes, as shown below:
+@smallexample
+void __attribute__ ((interrupt)) v0 ();
+void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
+void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
+void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
+void __attribute__ ((interrupt, use_shadow_register_set,
+ keep_interrupts_masked)) v4 ();
+void __attribute__ ((interrupt, use_shadow_register_set,
+ use_debug_exception_return)) v5 ();
+void __attribute__ ((interrupt, keep_interrupts_masked,
+ use_debug_exception_return)) v6 ();
+void __attribute__ ((interrupt, use_shadow_register_set,
+ keep_interrupts_masked,
+ use_debug_exception_return)) v7 ();
+@end smallexample
+
@item interrupt_handler
@cindex interrupt handler functions on the Blackfin, m68k, H8/300 and SH processors
Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to
This attribute can be used to cancel the effect of the @option{-mlong-calls}
option.
+On MeP targets this attribute causes the compiler to assume the called
+function is close enough to use the normal calling convention,
+overriding the @code{-mtf} command line option.
+
@item nesting
@cindex Allow nesting in an interrupt handler on the Blackfin processor.
Use this attribute together with @code{interrupt_handler},
If both the template and enclosing class have explicit visibility, the
visibility from the template is used.
+@item vliw
+@cindex @code{vliw} attribute
+On MeP, the @code{vliw} attribute tells the compiler to emit
+instructions in VLIW mode instead of core mode. Note that this
+attribute is not allowed unless a VLIW coprocessor has been configured
+and enabled through command line options.
+
@item warn_unused_result
@cindex @code{warn_unused_result} attribute
The @code{warn_unused_result} attribute causes a warning to be emitted
that may be unused but which is compiled with @option{-Wall}. It would
not normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
-contained within an @code{#ifdef} conditional. GNU C++ does not permit
-such placement of attribute lists, as it is permissible for a
-declaration, which could begin with an attribute list, to be labelled in
-C++. Declarations cannot be labelled in C90 or C99, so the ambiguity
-does not arise there.
+contained within an @code{#ifdef} conditional. GNU C++ only permits
+attributes on labels if the attribute specifier is immediately
+followed by a semicolon (i.e., the label applies to an empty
+statement). If the semicolon is missing, C++ label attributes are
+ambiguous, as it is permissible for a declaration, which could begin
+with an attribute list, to be labelled in C++. Declarations cannot be
+labelled in C90 or C99, so the ambiguity does not arise there.
An attribute specifier list may appear as part of a @code{struct},
@code{union} or @code{enum} specifier. It may go either immediately
@option{-fno-common} and @option{-fcommon} flags respectively.
@item deprecated
+@itemx deprecated (@var{msg})
@cindex @code{deprecated} attribute
The @code{deprecated} attribute results in a warning if the variable
is used anywhere in the source file. This is useful when identifying
int new_fn () @{ return old_var; @}
@end smallexample
-results in a warning on line 3 but not line 2.
+results in a warning on line 3 but not line 2. The optional msg
+argument, which must be a string, will be printed in the warning if
+present.
The @code{deprecated} attribute can also be used for functions and
types (@pxref{Function Attributes}, @pxref{Type Attributes}.)
addresses).
@end table
+@anchor{MeP Variable Attributes}
+@subsection MeP Variable Attributes
+
+The MeP target has a number of addressing modes and busses. The
+@code{near} space spans the standard memory space's first 16 megabytes
+(24 bits). The @code{far} space spans the entire 32-bit memory space.
+The @code{based} space is a 128 byte region in the memory space which
+is addressed relative to the @code{$tp} register. The @code{tiny}
+space is a 65536 byte region relative to the @code{$gp} register. In
+addition to these memory regions, the MeP target has a separate 16-bit
+control bus which is specified with @code{cb} attributes.
+
+@table @code
+
+@item based
+Any variable with the @code{based} attribute will be assigned to the
+@code{.based} section, and will be accessed with relative to the
+@code{$tp} register.
+
+@item tiny
+Likewise, the @code{tiny} attribute assigned variables to the
+@code{.tiny} section, relative to the @code{$gp} register.
+
+@item near
+Variables with the @code{near} attribute are assumed to have addresses
+that fit in a 24-bit addressing mode. This is the default for large
+variables (@code{-mtiny=4} is the default) but this attribute can
+override @code{-mtiny=} for small variables, or override @code{-ml}.
+
+@item far
+Variables with the @code{far} attribute are addressed using a full
+32-bit address. Since this covers the entire memory space, this
+allows modules to make no assumptions about where variables might be
+stored.
+
+@item io
+@item io (@var{addr})
+Variables with the @code{io} attribute are used to address
+memory-mapped peripherals. If an address is specified, the variable
+is assigned that address, else it is not assigned an address (it is
+assumed some other module will assign an address). Example:
+
+@example
+int timer_count __attribute__((io(0x123)));
+@end example
+
+@item cb
+@item cb (@var{addr})
+Variables with the @code{cb} attribute are used to access the control
+bus, using special instructions. @code{addr} indicates the control bus
+address. Example:
+
+@example
+int cpu_clock __attribute__((cb(0x123)));
+@end example
+
+@end table
+
@anchor{i386 Variable Attributes}
@subsection i386 Variable Attributes
@};
@end smallexample
-You may only specify this attribute on the definition of a @code{enum},
+You may only specify this attribute on the definition of an @code{enum},
@code{struct} or @code{union}, not on a @code{typedef} which does not
also define the enumerated type, structure or union.
nontrivial bookkeeping functions.
@item deprecated
+@itemx deprecated (@var{msg})
The @code{deprecated} attribute results in a warning if the type
is used anywhere in the source file. This is useful when identifying
types that are expected to be removed in a future version of a program.
results in a warning on line 2 and 3 but not lines 4, 5, or 6. No
warning is issued for line 4 because T2 is not explicitly
deprecated. Line 5 has no warning because T3 is explicitly
-deprecated. Similarly for line 6.
+deprecated. Similarly for line 6. The optional msg
+argument, which must be a string, will be printed in the warning if
+present.
The @code{deprecated} attribute can also be used for functions and
variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.)
@code{__attribute__} instead of @code{__declspec} if you prefer, but
most Symbian OS code uses @code{__declspec}.)
+@anchor{MeP Type Attributes}
+@subsection MeP Type Attributes
+
+Many of the MeP variable attributes may be applied to types as well.
+Specifically, the @code{based}, @code{tiny}, @code{near}, and
+@code{far} attributes may be applied to either. The @code{io} and
+@code{cb} attributes may not be applied to types.
+
@anchor{i386 Type Attributes}
@subsection i386 Type Attributes
The types defined in this manner can be used with a subset of normal C
operations. Currently, GCC will allow using the following operators
-on these types: @code{+, -, *, /, unary minus, ^, |, &, ~}@.
+on these types: @code{+, -, *, /, unary minus, ^, |, &, ~, %}@.
The operations behave like C++ @code{valarrays}. Addition is defined as
the addition of the corresponding elements of the operands. For
constant expression, including the case where
@code{__builtin_constant_p} returns 1 because @var{EXPRESSION} can be
folded to a constant but @var{EXPRESSION} contains operands that would
-not otherwize be permitted in a static initializer (for example,
+not otherwise be permitted in a static initializer (for example,
@code{0 && foo ()}). GCC must be more conservative about evaluating the
built-in in this case, because it has no opportunity to perform
optimization.
you should not rely on any particular implementation.
@end deftypefn
+@deftypefn {Built-in Function} void __builtin_unreachable (void)
+If control flow reaches the point of the @code{__builtin_unreachable},
+the program is undefined. It is useful in situations where the
+compiler cannot deduce the unreachability of the code.
+
+One such case is immediately following an @code{asm} statement that
+will either never terminate, or one that transfers control elsewhere
+and never returns. In this example, without the
+@code{__builtin_unreachable}, GCC would issue a warning that control
+reaches the end of a non-void function. It would also generate code
+to return after the @code{asm}.
+
+@smallexample
+int f (int c, int v)
+@{
+ if (c)
+ @{
+ return v;
+ @}
+ else
+ @{
+ asm("jmp error_handler");
+ __builtin_unreachable ();
+ @}
+@}
+@end smallexample
+
+Because the @code{asm} statement unconditionally transfers control out
+of the function, control will never reach the end of the function
+body. The @code{__builtin_unreachable} is in fact unreachable and
+communicates this fact to the compiler.
+
+Another use for @code{__builtin_unreachable} is following a call a
+function that never returns but that is not declared
+@code{__attribute__((noreturn))}, as in this example:
+
+@smallexample
+void function_that_never_returns (void);
+
+int g (int c)
+@{
+ if (c)
+ @{
+ return 1;
+ @}
+ else
+ @{
+ function_that_never_returns ();
+ __builtin_unreachable ();
+ @}
+@}
+@end smallexample
+
+@end deftypefn
+
@deftypefn {Built-in Function} void __builtin___clear_cache (char *@var{begin}, char *@var{end})
This function is used to flush the processor's instruction cache for
the region of memory between @var{begin} inclusive and @var{end}
@item unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)
Generates the @code{crc32l} machine instruction.
@item unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long)
+Generates the @code{crc32q} machine instruction.
@end table
The following built-in functions are changed to generate new SSE4.2
@menu
* ARM Pragmas::
* M32C Pragmas::
+* MeP Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
@end table
+@node MeP Pragmas
+@subsection MeP Pragmas
+
+@table @code
+
+@item custom io_volatile (on|off)
+@cindex pragma, custom io_volatile
+Overrides the command line option @code{-mio-volatile} for the current
+file. Note that for compatibility with future GCC releases, this
+option should only be used once before any @code{io} variables in each
+file.
+
+@item GCC coprocessor available @var{registers}
+@cindex pragma, coprocessor available
+Specifies which coprocessor registers are available to the register
+allocator. @var{registers} may be a single register, register range
+separated by ellipses, or comma-separated list of those. Example:
+
+@example
+#pragma GCC coprocessor available $c0...$c10, $c28
+@end example
+
+@item GCC coprocessor call_saved @var{registers}
+@cindex pragma, coprocessor call_saved
+Specifies which coprocessor registers are to be saved and restored by
+any function using them. @var{registers} may be a single register,
+register range separated by ellipses, or comma-separated list of
+those. Example:
+
+@example
+#pragma GCC coprocessor call_saved $c4...$c6, $c31
+@end example
+
+@item GCC coprocessor subclass '(A|B|C|D)' = @var{registers}
+@cindex pragma, coprocessor subclass
+Creates and defines a register class. These register classes can be
+used by inline @code{asm} constructs. @var{registers} may be a single
+register, register range separated by ellipses, or comma-separated
+list of those. Example:
+
+@example
+#pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6
+
+asm ("cpfoo %0" : "=B" (x));
+@end example
+
+@item GCC disinterrupt @var{name} , @var{name} @dots{}
+@cindex pragma, disinterrupt
+For the named functions, the compiler adds code to disable interrupts
+for the duration of those functions. Any functions so named, which
+are not encountered in the source, cause a warning that the pragma was
+not used. Examples:
+
+@example
+#pragma disinterrupt foo
+#pragma disinterrupt bar, grill
+int foo () { @dots{} }
+@end example
+
+@item GCC call @var{name} , @var{name} @dots{}
+@cindex pragma, call
+For the named functions, the compiler always uses a register-indirect
+call model when calling the named functions. Examples:
+
+@example
+extern int foo ();
+#pragma call foo
+@end example
+
+@end table
+
+
@node RS/6000 and PowerPC Pragmas
@subsection RS/6000 and PowerPC Pragmas
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