Re: What is the simplest CPU GCC is ported for?



Steve Calfee <stevecalfee@xxxxxxxxxxx> posted:

"[..]

GCC in its bones believes in 8 bit bytes, words being some multiple of
bytes etc. There are lots of built in assumptions based on the cpu
architectures in existance now. I think it would be hard to port to a
bit addressable cpu.

[..]"

Maybe. In a later post in this thread you said you wanted 32 bit
support so I do not know whether you want to support "a bit
addressable" CPU as well, or whether that was merely an auxiliary
comment.

The 1750a configuration which used to be in GCC but had been removed
many version numbers ago from the versions maintained by the Free
Software Foundation (as someone supporting a GCC configuration for the
MIL-STD-1750A processor was being paid by providing support directly
to customers instead of telling them to download GCC for gratis from
the FSF) contained "#define BITS_PER_UNIT 16". "#define
BITS_PER_UNIT 32" is in gcc-4.1.1/gcc/config/c4x/c4x.h

From
info gccint
:"[..]

Here is a table of machine modes. The term "byte" below refers to an
object of `BITS_PER_UNIT' bits (*note Storage Layout::).

[..]

The global variables `byte_mode' and `word_mode' contain modes whose
classes are `MODE_INT' and whose bitsizes are either `BITS_PER_UNIT'
or
`BITS_PER_WORD', respectively. [..]

-- Macro: BITS_PER_UNIT
Define this macro to be the number of bits in an addressable
storage unit (byte). If you do not define this macro the default
is 8.

-- Macro: BITS_PER_WORD
Number of bits in a word. If you do not define this macro, the
default is `BITS_PER_UNIT * UNITS_PER_WORD'.

[..]"
.