Re: i370 port

["Paul Edwards" <mutazilah at gmail dot com>]

> > I then found out that even with old versions of the machine definition,
> > I can have the warning removed by simply not defining CONST_INT
> > in the PREDICATE_CODES, even though it is allowed when the
> > function is called.  ie it seems to have no effect on the code
> > generation, but succeeds in eliminating the warning, and without
> > needing to define an extra constraint for non-constant situations.
>
> Actually PREDICATE_CODES does have to match the predicate definitions.
> If it does not, you can run into subtle bugs, as the code in genrecog.c
> that generates the finite state automaton matching an RTX pattern
> against the .md insn definitions *does* make use of PREDICATE_CODES;
> for example, it will assume that two predicates with disjoint sets
> of PREDICATE_CODES can never both match the same RTX.
>
> This may or may not lead to visible differences when compiling simple
> test cases, but I'd expect effects to be visible in more complex
> scenarios.

Thanks Ulrich.  When I went back to this I found that I had
misdiagnosed - actually the r_or_s didn't allow constants after
all.  It was only const_rtx that it allowed.  So the machine definition
no longer has any warnings and all looks good.

That's with 3.2.3.

With 3.4.6 I have now managed to get an MVS load module,
unoptimized (I already know that optimized doesn't work), to
compile a hello world program successfully, although it abends
at the end of that and I haven't investigated that yet.

So the theoretical EBCDIC support is less theoretical now.
I "needed" to change the parameter search algorithm to stop
being binary search though.

GCC 4 complained (on my Linux system) that I didn't have
various things (gimp etc) installed, which means I would need
that other software to be ported too, which is not a project
I want to work on at the moment.  However, at least it means
that i have successfully merged all the GCCMVS changes
to 3.2.3 in with the (last available) 3.4.6 development, which
was a precursor to any GCC 4 port anyway.  I'll see over time
how GCC 3.4.6 pans out.

Until then, back at GCC 3.2.3, I have a "need" to make the entry
point 0 in my MVS modules.

Currently I generate this:

        COPY  PDPTOP
        CSECT
* X-var bytes
        ENTRY BYTES
* Program data area
        DS    0F
BYTES    EQU   *
        DC    F'258'
* Program text area
LC0      EQU   *
        DC    C'bytes is %d'
        DC    X'15'
        DC    X'0'
        DS    0F
        DC    C'GCCMVS!!'
        EXTRN @@CRT0
        ENTRY @@MAIN
@@MAIN   DS    0H
        USING *,15
        L     15,=V(@@CRT0)
        BR    15
        DROP  15
        LTORG
* X-func main prologue
MAIN     PDPPRLG CINDEX=0,FRAME=96,BASER=12,ENTRY=YES
...
* Function main page table
        DS    0F
PGT0     EQU   *
        DC    A(PG0)
        END   @@MAIN

for a main program.  In order to get the entry point to 0, I need to move 
that
@@MAIN function to the top of the file.

But I only really want that function if this is a main program.  I have 
found
somewhere where I can add some code to see if the function "main" is
being compiled, and set a global variable.

Unfortunately, the place that happens (c-decl) isn't called until after all
the data has been written out!

I looked at the documentation:

http://gcc.gnu.org/onlinedocs/gcc-3.2.3/gccint/Assembler-Format.html#Assembler%20Format

but maybe I'm looking in the wrong place.  Any ideas?

And I have another question - where is the code for __asm__?

Currently that is generating garbage for me:

unsigned int bytes = 258;

__asm__("? :");

int main(void)

BYTES    EQU   *
        DC    F'258'
        o@z
* Program text area

when done in cross-compiler mode, and need to find out where
the literal is being translated (or more likely - failing to be
translated in the first instance).  Any idea where that is?

And final thing - the interest in the __asm__ comes from the hope
that in the generated 370 assembler, it would be possible to have
the C code interspersed to whatever extent possible.  The plan was
to basically somehow get every line of C code, e.g. "int main(void)"
above, and automatically generate an:
__asm__("int main void)");

although I'm not sure what to do about this:

int main(void)
__asm__("? :");
{

which gives a syntax error.  Any idea how to get the mixed
C/assembler when I'm running with the "-S" option and don't
have the luxury of calling the normal "as" which would
normally handle that?

Thanks.  Paul.