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

[Jeff Law <law@redhat.com>]

On 04/23/2015 09:10 PM, Thomas Preud'homme wrote:
>> 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
Missed that message.  Given we've already gone round and round on it, 
let go with the patch as-is and deal with hard_register_p and 
pseudo_register_p independently.  No idea who objected to that, seems 
like a no-brainer to me.

>
>>
>>> @@ -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.
Ah.  Nevermind then.

So revised review is "ok for the trunk" :-)

jeff