Re: [RFC] Enable saliasing for structs with arrays

[Richard Guenther <rguenther at suse dot de>]

On Tue, 19 Jul 2005, Zdenek Dvorak wrote:

> Hello,
> 
> > > This simple patch enables structure aliasing for structs containing
> > > arrays (_not_ enabling subvars for the arrays).  Unfortunately, the
> > > patch breaks bootstrap due to IVOPTs and friends.  This is sad, as
> > > it may even help for better alias analysis for GCCs tree structure.
> > > 
> > > Maybe some IVOPTs folks can help out here.
> 
> tree-ssa-loop-ivopts.c:copy_ref_info does not handle the subvars at all,
> currently. I will check what I can do.

For TARGET_MEM_REFs being nice to me (i.e. have a TMR_SYMBOL) I was
able to fix the aliasing issues.  But now, f.i. for the testcase

static union {
  char buf[100];
  double foo;
} u2;

extern void foobar (char *);
main ()
{
  int off2, len;
  char *p;
  for (len = 1; len < 100; len++)
    {
      u2.buf[off2 + len] = '\0';
      foobar (u2.buf + off2);
    }

  return 0;
}

we generate TARGET_MEM_REFs with neither TMR_SYMBOL, nor TMR_TAG for
'u2.buf[off2 + len] = '\0';' -- this sucks.  TARGET_MEM_REFs would
fit nicely with subvars and aliasing, if they only always had all
necessary information filled in.

Richard.