[PATCH] PR middle-end/103059: reload: Also accept ASHIFT with indexed addressing

[Jeff Law]

On 11/4/2021 6:18 PM, Maciej W. Rozycki wrote:
> On Thu, 4 Nov 2021, Jeff Law wrote:
>
>> Sometimes the language we're using in email is not as crisp as it should be.  So
>> just to be clear, the canonicalization I'm referring to is only in effect within
>> a MEM.  It does not apply to address calculations that happen outside a MEM.  I
>> think that is consistent with Richard's comments.
>   Ah, OK then.
>
>>> and then reload substitutes (reg/v:SI 154 [ n_ctrs ]) with the inner MEM
>>> as it fails to reload the pseudo and just uses its memory location.
>> OK.  So what I still don't see is why  we would need to re-recognize.   You're
>> changing code that I thought was only applicable when we were reloading an
>> address inside a MEM and if we're inside a MEM, then we shouldn't be seeing an
>> ASHIFT.   We're replacing the argument of the ASHIFT.
>   Well, the context of this code (around and including hunk #1) is:
>
>        else if (insn_extra_address_constraint
> 	       (lookup_constraint (constraints[i])))
> 	{
> 	  address_operand_reloaded[i]
> 	    = find_reloads_address (recog_data.operand_mode[i], (rtx*) 0,
> 				    recog_data.operand[i],
> 				    recog_data.operand_loc[i],
> 				    i, operand_type[i], ind_levels, insn);
>
> 	  /* If we now have a simple operand where we used to have a
> 	     PLUS or MULT, re-recognize and try again.  */
> 	  if ((OBJECT_P (*recog_data.operand_loc[i])
> 	       || GET_CODE (*recog_data.operand_loc[i]) == SUBREG)
> 	      && (GET_CODE (recog_data.operand[i]) == MULT
> 		  || GET_CODE (recog_data.operand[i]) == PLUS))
> 	    {
> 	      INSN_CODE (insn) = -1;
> 	      retval = find_reloads (insn, replace, ind_levels, live_known,
> 				     reload_reg_p);
> 	      return retval;
> 	    }
>
> so the body of the conditional is specifically executed for an address and
> not a MEM; in this particular case matched with the plain "p" constraint.
>
>   MEMs are handled with the next conditional right below.
Ah!  Thanks for the clarification.  We're digging deep into history 
here.  I always thought this code was re-recognizing inside a MEM, but 
as you note, it's actually handling stuff outside the MEM, such as  a 
'p' constraint, which is an address, but being outside a MEMS means its 
not subject to the mult-by-power-of-2 canonicalization.

So I think the first hunk is fine.  There's two others that twiddle 
find_reloads_address_1, which I think can only be reached from 
find_reloads_address.  The comment at the front would indicate it's only 
called where AD is inside a MEM.

Are we getting into find_reloads_address_1 in any case where the RTL is 
not an address inside a MEM?

jeff