Re: Register numbers in RTL dumps (was Re: [PATCH 0/9] RFC: selftests based on RTL dumps)

[David Malcolm <dmalcolm at redhat dot com>]

On Tue, 2016-09-20 at 09:20 -0600, Jeff Law wrote:
> On 09/20/2016 08:34 AM, Bernd Schmidt wrote:
> > On 09/20/2016 04:32 PM, David Malcolm wrote:
> > > 
> > > To summarize so far: you want every pseudo to have its regno
> > > dumped
> > > with a 'p' prefix, and renumber them on dump (and then on load).
> > > OK.
> > 
> > Renumbering is not helpful because it interferes with the view you
> > have
> > in the debugger. So, IMO just a prefix, and maybe
> Yea, I guess it does since we want the numbers in the dump to be the 
> same that we used to access the arrays.  So prefixing in the dump
> with 
> adjustment of the number in the reader.

To check I understand: am I right in thinking you want:
(A) the numbers in the dump to be unmodified when dumping, so that we
can easily look up values in arrays without confusion, and
(B) regnums in the dump gain a 'p' prefix for values >=
 FIRST_PSEUDO_REGISTER, so that humans and parsers can easily see when
the regs are pseudos, and that
(C) the parser will detect if a 'p'-prefixed regno actually has the
same number as a hard reg (which can happen e.g. when a .md file
changes, or when sharing .rtl dumps between targets), and remap the
values on load accordingly

?

(in which case we do need the regno_remapper class, or something like
it)

> > 
> > >   (reg/f:DI v1 virtual-stack-vars)
> > 
> > this.
> Doesn't the same apply to the number of virtual stack regs?  Those
> are 
> in the same array as pseudos.  So ISTM we prefix in the dump, but do 
> adjustment of the number in the reader?

Presumably we could use "v" rather than "p" as the prefix for the first
5 pseudos (up to LAST_VIRTUAL_REGISTER), doing any adjustment at load
time, rather than at dump time.  So the above example would look like:

   (reg/f:DI v82 virtual-stack-vars)

i.e. the 82 for x86_64's virtual-stack-vars would be prefixed with a
'v', and the loader would adjust it to be the current target's value
for VIRTUAL_STACK_VARS_REGNUM.

Do you like the idea of prefixing regnums of hardregs with 'h'? (so
that all regnos get a one-char prefix) e.g.
  (reg/i:SI h0 ax)
  (reg/i:SF h21 xmm0)


Dave