The SUIF library includes a structure to record various parameters of
the target machine. The back-end of the compiler may be either a code
generator for a specific processor or the system's C compiler, using the
SUIF-to-C translator. Thus, the target machine parameters include
fields that deal both with hardware requirements and with details of the
back-end C compiler. These parameters are stored in the target
machine_params structure. The front-end is responsible for
setting the target parameters, but they are then saved in the SUIF files
and passed along to all subsequent passes of the compiler.
The first fields in the machine_params structure deal with the
addressing in the underlying hardware. The is_big_endian field
specifies the byte order, and the addressable_size field
specifies the size in bits of the smallest addressable unit. Since most
machines are byte-addressable, the addressable_size is usually
set to eight.
Next, the sizes and alignments for various C types are specified. The
possible C types are listed in the C_types enumeration:
C_char
C_short
C_int
C_long
C_longlong
C_float
C_double
C_longdouble
C_ptr
The size and align fields of the machine_params
structure are arrays containing the size and alignment for each C type.
Both are specified in bits (not bytes). Some C compilers require
additional alignment restrictions for arrays and structures. The
array_align and struct_align fields contain these
alignment requirements in bits. Note that these do not replace the
alignment restrictions for the components of an array or structure; the
most restrictive alignments must always be maintained.
The remaining fields are only applicable to the back-end C compiler.
The char_is_signed field specifies if the default char
type is signed. This is just to allow the SUIF-to-C translator to avoid
cluttering up the C code by explicitly putting signed or
unsigned in every declaration of a char type. When two
pointers are subtracted in C, the result type is implementation defined.
The ptr_diff_type field in machine_params specifies the
type produced by such pointer subtractions for use in SUIF-to-C.