Re: [PATCH], V4, patch #9 [part of patch #4.2], Add prefixed address offset checks

[Michael Meissner <meissner at linux dot ibm dot com>]

On Wed, Oct 09, 2019 at 04:56:48PM -0500, Segher Boessenkool wrote:
> Hi!
> 
> On Fri, Oct 04, 2019 at 08:29:11AM -0400, Michael Meissner wrote:
> > @@ -8651,6 +8675,11 @@ rs6000_legitimate_address_p (machine_mod
> >        && mode_supports_pre_incdec_p (mode)
> >        && legitimate_indirect_address_p (XEXP (x, 0), reg_ok_strict))
> >      return 1;
> > +
> > +  /* Handle prefixed addresses (PC-relative or 34-bit offset).  */
> > +  if (address_is_prefixed (x, mode, NON_PREFIXED_DEFAULT))
> > +    return 1;
> 
> Is this correct?  Are addresses with a larger offset always legitimate?
> I don't see why that would be the case.
> 
> The rest of the patch looks good, thanks.

As far as I know, with the exception of SDmode (which is not allowed to have an
offset) all other modes that use D*-form addresses would work with a prefixed
instruction, assuming the offset fits in the 34-bit field.

The function address_to_insn_form, which is called by address_is_prefixed,
checks if the offset is 34-bits or less, whether the mode is SDmode, etc. are
all valid.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797