Argument passing

[Michael P. Hayes]

Ivo Janssen writes:
 > Hello,
 > 
 > I have the following problem:
 > My 16 processor does not have a multiply. So I wrote an 
 > emulator-function which does repeated adds, named __mulqi3.
 > QI because 16bit=1 storage unit. int is also 16 bit. (QI)
 > The compiler is supposed to pass args in "r0", "r1" to "r4".
 > The rest via stack.
 > 
 > But when I do int a=12; int b=34; c=a*b;
 > the compiler puts 12 in "r10", 34 in "r6" and expects the return value 
 > in "r3", instead of "r0". And, it calles __mulsi3. So it is expecting 
 > 4-word values, instead of 1word values (remember, word=16bit).
 > 
 > How can I instruct the compiler to use __mulqi3 with exactly 1 word (=1 
 > register) wide arguments?

I have had similar problems with porting the TMS320C[34]x DSPs where
BITS_PER_UNIT = 32 and BITS_PER_WORD = 32.  I had to patch optabs.c to
get the libcalls to work.  Unfortunately, libgcc2 is broken for
processors where BITS_PER_UNIT != 8.


Index: optabs.c
===================================================================
RCS file: /usr/local/src/cvsroot/gnu/gcc/optabs.c,v
retrieving revision 1.1.1.1
retrieving revision 1.2.2.1
diff -c -r1.1.1.1 -r1.2.2.1
*** optabs.c	1997/07/09 02:21:49	1.1.1.1
--- optabs.c	1997/09/18 03:20:13	1.2.2.1
***************
*** 3965,3971 ****
      register char *opname;
      register int suffix;
  {
!   init_libfuncs (optable, SImode, TImode, opname, suffix);
  }
  
  /* Initialize the libfunc fields of an entire group of entries in some
--- 3965,3971 ----
      register char *opname;
      register int suffix;
  {
!   init_libfuncs (optable, QImode, TImode, opname, suffix);
  }
  
  /* Initialize the libfunc fields of an entire group of entries in some
***************
*** 3979,3985 ****
      register char *opname;
      register int suffix;
  {
!   init_libfuncs (optable, SFmode, TFmode, opname, suffix);
  }
  
  /* Initialize the libfunc fields of an entire group of entries in some
--- 3979,3985 ----
      register char *opname;
      register int suffix;
  {
!   init_libfuncs (optable, QFmode, TFmode, opname, suffix);
  }
  
  /* Initialize the libfunc fields of an entire group of entries in some