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

["Maciej W. Rozycki" <macro@embecosm.com>]

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.

> So, overall, I'm still confused as to why the patch has any effect at all.

 Does the explanation above clear your confusion?

  Maciej