When a function value’s mode is
BLKmode (and in some other
cases), the value is not returned according to
TARGET_FUNCTION_VALUE (see Scalar Return). Instead, the
caller passes the address of a block of memory in which the value
should be stored. This address is called the structure value
This section describes how to control returning structure values in memory.
This target hook should return a nonzero value to say to return the
function value in memory, just as large structures are always returned.
Here type will be the data type of the value, and fntype
will be the type of the function doing the returning, or
Note that values of mode
BLKmode must be explicitly handled
by this function. Also, the option -fpcc-struct-return
takes effect regardless of this macro. On most systems, it is
possible to leave the hook undefined; this causes a default
definition to be used, whose value is the constant 1 for
values, and 0 otherwise.
Do not use this hook to indicate that structures and unions should always
be returned in memory. You should instead use
to indicate this.
Define this macro to be 1 if all structure and union return values must be
in memory. Since this results in slower code, this should be defined
only if needed for compatibility with other compilers or with an ABI.
If you define this macro to be 0, then the conventions used for structure
and union return values are decided by the
If not defined, this defaults to the value 1.
This target hook should return the location of the structure value
address (normally a
reg), or 0 if the address is
passed as an “invisible” first argument. Note that fndecl may
NULL, for libcalls. You do not need to define this target
hook if the address is always passed as an “invisible” first
On some architectures the place where the structure value address
is found by the called function is not the same place that the
caller put it. This can be due to register windows, or it could
be because the function prologue moves it to a different place.
2 when the location is needed in
the context of the called function, and
0 in the context of
If incoming is nonzero and the address is to be found on the
stack, return a
mem which refers to the frame pointer. If
2, the result is being used to fetch the
structure value address at the beginning of a function. If you need
to emit adjusting code, you should do it at this point.
Define this macro if the usual system convention on the target machine for returning structures and unions is for the called function to return the address of a static variable containing the value.
Do not define this if the usual system convention is for the caller to pass an address to the subroutine.
This macro has effect in -fpcc-struct-return mode, but it does nothing when you use -freg-struct-return mode.
This target hook returns the mode to be used when accessing raw return
__builtin_return. Define this macro if the value
in reg_raw_mode is not correct.
This target hook returns the mode to be used when accessing raw argument
__builtin_apply_args. Define this macro if the value
in reg_raw_mode is not correct.
This target hook returns true if the type is an empty record. The default
is to return
This target hook warns about the change in empty class parameter passing ABI.