[PATCH, GCC, stage1] Fallback to copy-prop if constant-prop not possible

[Steven Bosscher]

On Fri, Mar 20, 2015 at 11:27 AM, Thomas Preud'homme wrote:
> Sorry, I missed the parenthesis. REG_P needs indeed to be kept. I'd be
> tempted to use !HARD_REGISTER_P instead since REG_P is already
> checked but I don't mind either way.

I put the cprop_reg_p check there instead of !HARD_REGISTER_P because
I like to be able to quickly find all places where a similar check is
performed. The check is whether the reg is something that copy
propagation can handle, and that is what I added cprop_reg_p for.
(Note that cprop can _currently_ handle only pseudos but there is no
reason why a limited set of hard regs can't be handled also, e.g. the
flag registers like in targetm.fixed_condition_code_regs).

In this case, the result is that REG_P is checked twice.
But then again, cprop_reg_p will be inlined and the double check optimized away.

Anyway, I guess we've bikeshedded long enough over this patch as it is
:-) Let's post a final form and declare it OK for stage1.

As for PSEUDO_REG_P: If it were up to me, I'd like to have in rtl.h:

static bool
hard_register_p (rtx x)
{
  return (REG_P (x) && HARD_REGISTER_NUM_P (REGNO (x)));
}

static bool
pseudo_register_p (rtx x)
{
  return (REG_P (x) && !HARD_REGISTER_NUM_P (REGNO (x)));
}

and do away with all the FIRST_PSEUDO_REGISTER tests. But I've
proposed this in the past and there was opposition. Perhaps when we
introduce a rtx_reg class...

Ciao!
Steven