Re: [PATCH] IRA: Don't create new regs for debug insns (PR80429)

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Apr 18, 2017 at 09:30:19AM +0000, Segher Boessenkool wrote:
> In split_live_ranges_for_shrink_wrap IRA also splits regs that are
> only used in debug insns, leading to -fcompare-debug failures.
> 
> Bootstrapped and tested on powerpc64-linux {-m32,-m64}.  This happens
> on at least GCC 5, so not a regression; but it is trivial and obvious,
> is it okay for trunk anyway?

I think the first question here is if it is beneficial to replace the
regs in DEBUG_INSNs or not.  If it is beneficial, then it of course
has to be changed such that it never does
newreg = ira_create_new_reg (dest);
just because it sees DEBUG_INSN uses, but otherwise it should do what it
does now.

So one option is e.g. to split that loop into two, one doing analysis,
i.e. that newreg = ira_create_new_reg (dest);, but not
validate_change (uin, DF_REF_REAL_LOC (use), newreg, true);
and this loop would also ignore DEBUG_INSN_P.
And the other loop, with the same content, just without that newreg = ...
and with the validate_change, as whole guarded with if (newreg),
replacing stuff on all insns.

Or another way to write this is have the loop as currently is, with
  if (DEBUG_INSN_P (uin) && (!newreg || debug_insns_seen_p))
    {
      debug_insns_seen_p = true;
      continue;
    }
and then another loop done only if (debug_insns_seen_p && newreg)
that would only adjust DEBUG_INSNs.

	Jakub