Description
Variables inside a kernel function not declared with an
address space qualifier, all variables inside non-kernel functions, and all function
arguments are in the __private or private
address space.
Notes
General information about address space qualifiers
OpenCL implements the following disjoint named address
spaces: __global,
__local, __constant, and
__private. The address space qualifier may be used in variable
declarations to specify the region of memory that is used to allocate the object. The
C syntax for type qualifiers is extended in OpenCL
to include an address space name as a valid type qualifier.
If the type of an object is qualified by an address
space name, the object is allocated in the
specified address name; otherwise, the object is
allocated in the generic address space.
The address space names without the __ prefix i.e. global,
local, constant
and private
may be substituted for the corresponding address
space names with the __ prefix.
The address space name for arguments to a function
in a program, or local variables of a function
is __private. All function
arguments shall be in the __private address space.
The address space for a variable at program scope
or a static variable inside a function can either
be __global or
__constant, but defaults to
__global if not specified.
OpenCL 2.0 adds support for an unnamed generic
address space. Pointers that are declared
without pointing to a named address space point to the
generic address space. Before
referring to the region pointed to, the pointer
must be associated with a named address space.
Functions may be written with arguments and return values that point to the
generic address space.
kernel function arguments declared to be a pointer or
an array of a type must point to one of
the named address spaces __global,
__local or __constant.
The named address spaces are a subset of the generic
address space except for the constant
address space.
A pointer to address space A can only be assigned to
a pointer to the same address space A or a
pointer to the generic address
space. Casting a pointer to address space A to a pointer to
address space B is illegal if A and B are named
address spaces and A is not the same as B.
The __global, __constant,
__local,
__private, __generic,
global,
constant, local, and
private names are reserved for use as address space
qualifiers and shall not be used otherwise.
The __generic and generic
names are reserved for future use.
The size of pointers to different address spaces
may differ. It is not correct to assume
that, for example, sizeof(__global int *)
always equals sizeof(__local int *).
Example
General qualifier examples follow:
| // declares a pointer p in the private address space that // points to an object in address space global global int *p; void foo (...) { // declares an array of 4 floats in the private address space float x[4]; ... } |
Example:
| private int f() { ... } // should generate an error local int *f() { ... } // allowed local int * private f() { ... }; // should generate an error. |
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