Re: [RFA] sh-tdep.c (sh_use_struct_convention): Restructure and fix

[Corinna Vinschen <vinschen@redhat.com>]

On Fri, Oct 10, 2003 at 09:29:29AM +0200, Corinna Vinschen wrote:
> And even though I have to admit, that I'm not 100% sure (perhaps
> I miss a case) I think the implementation should match at least 99%
> of the description. 
> 
> The difference between the old and the new code is given by allowing
> 4 byte structs (erm, aggregates) with more than one element, but a size
> of 4 byte for the first element.  This sounds somewhat weird, but that's
> exactly the case if the 4 byte agregate is a bitfield or contains a
> bitfield.  So the change in this patch solves exactly these bitfields
> as return type problem.

...and I just found out what this patch does *not* cover.  It does
not cover the case of bitfields of size 1 or 2 bytes :-(

I rewrote the implementation of sh_use_struct_convention and tested it
again.  Below is the entire implementation instead of the patch.  I think
this is easier to read.  I also tried to match the comments even better
to the actual code.  Is that ok to check in?

Btw., this time, there *are* tests missing.  The testsuite doesn't check
for returning bitfield types of size 1 and 2 bytes.  I'm going to add
two tests to call-rt-st.exp which I hope to submit at least Monday.

Corinna

========== SNIP ===========
static int
sh_use_struct_convention (int gcc_p, struct type *type)
{
  int len = TYPE_LENGTH (type);
  int nelem = TYPE_NFIELDS (type);

  /* Non-power of 2 length types and types bigger than 8 bytes (which don't
     fit in two registers anyway) use struct convention.  */
  if (len != 1 && len != 2 && len != 4 && len != 8)
    return 1;

  /* Scalar types and aggregate types with exactly one field are aligned
     by definition.  They are returned in registers.  */
  if (nelem <= 1)
    return 0;

  /* If the first field in the aggregate has the same length as the entire
     aggregate type, the type is returned in registers.  */
  if (TYPE_LENGTH (TYPE_FIELD_TYPE (type, 0)) == len)
    return 0;

  /* If the size of the aggregate is 8 bytes and the first field is
     of size 4 bytes its alignment is equal to long long's alignment,
     so it's returned in registers.  */
  if (len == 8 && TYPE_LENGTH (TYPE_FIELD_TYPE (type, 0)) == 4)
    return 0;

  /* Otherwise use struct convention.  */
  return 1;
}
========== SNAP ===========


-- 
Corinna Vinschen
Cygwin Developer
Red Hat, Inc.