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

["Thomas Preud'homme" <thomas dot preudhomme at arm dot com>]

> From: Jeff Law [mailto:law@redhat.com]
> Sent: Friday, April 24, 2015 10:59 AM
> 

Hi Jeff,

> > +
> > +static bool
> > +cprop_reg_p (const_rtx x)
> > +{
> > +  return REG_P (x) && !HARD_REGISTER_P (x);
> > +}
> How about instead this move to a more visible location (perhaps a macro
> in regs.h or an inline function).  Then as a followup, change the
> various places that have this sequence to use that common definition
> that exist outside of cprop.c.

According to Steven this was proposed in the past but was refused (see
end of [1]).

[1] https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01066.html

> 
> > @@ -1191,7 +1192,7 @@ do_local_cprop (rtx x, rtx_insn *insn)
> >     /* Rule out USE instructions and ASM statements as we don't want
> to
> >        change the hard registers mentioned.  */
> >     if (REG_P (x)
> > -      && (REGNO (x) >= FIRST_PSEUDO_REGISTER
> > +      && (cprop_reg_p (x)
> >             || (GET_CODE (PATTERN (insn)) != USE
> >   	      && asm_noperands (PATTERN (insn)) < 0)))
> Isn't the REG_P test now redundant?

I made the same mistake when reviewing that change and indeed it's not.
Note the opening parenthesis before cprop_reg_p that contains a bitwise
OR expression. So in the case where cprop_reg_p is false, REG_P still
needs to be true.

We could keep a check on FIRST_PSEUDO_REGISTER but the intent (checking
that the register is suitable for propagation) is clearer now, as pointed out by
Steven to me.

> 
> OK for the trunk with those changes.
> 
> jeff

Given the above I intent to keep the REG_P in the second excerpt and will
wait for your input about moving cprop_reg_p to rtl.h

Best regards,

Thomas