Re: Bug in reload_cse_move2add()

[amylaar at cambridge dot redhat dot com]

[Apologies if this appears twice - I've sent a similar message yesterday, but
 it seems to have been lost.]

In article <ork88fju0g.fsf@guarana.lsd.ic.unicamp.br> you wrote:
: Here's a patch that arranges for us to record the original offset when
: we copy from a register, so that we can tell by how much it has
: changed when we attempt to optimize away a new copy.  I see this
: infrastructure may enable a number of additional optimizations, by
: simply updating reg_offset without touching reg_set_luid when a
: register is inc/decremented and its reg_offset is already a CONST_INT,
: but I'll leave them for a separate patch, some other day (if I had
: posted this yesterday, I'd have said for the next millennium, but it's
: too late now :-)

If you just want to fix the bug, it should be sufficient to update the luid,
like this:

Index: reload1.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/reload1.c,v
retrieving revision 1.248
diff -p -r1.248 reload1.c
*** reload1.c	2001/01/02 00:59:52	1.248
--- reload1.c	2001/01/03 18:54:58
*************** move2add_note_store (dst, set, data)
*** 9149,9159 ****
  	      {
  		if (REGNO (src0) != regno
  		    || reg_offset[regno] != const0_rtx)
! 		  {
! 		    reg_base_reg[regno] = REGNO (src0);
! 		    reg_set_luid[regno] = move2add_luid;
! 		  }
  
  		reg_offset[regno] = XEXP (src, 1);
  		break;
  	      }
--- 9149,9157 ----
  	      {
  		if (REGNO (src0) != regno
  		    || reg_offset[regno] != const0_rtx)
! 		  reg_base_reg[regno] = REGNO (src0);
  
+ 		reg_set_luid[regno] = move2add_luid;
  		reg_offset[regno] = XEXP (src, 1);
  		break;
  	      }

OTOH, if you want to optimize these cases better, you can canonocalize the
reg_base_reg / reg_offset entries to refer to the earliest register.  This
gives some additional optimization opportunities, and doesn't need an extra
array:

Index: reload1.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/reload1.c,v
retrieving revision 1.248
diff -p -r1.248 reload1.c
*** reload1.c	2001/01/02 00:59:52	1.248
--- reload1.c	2001/01/03 19:43:12
*************** reload_cse_move2add (first)
*** 9011,9017 ****
  				  ...
  				  (set (REGX) (plus (REGX) (CONST_INT B-A)))  */
  	      else if (GET_CODE (src) == REG
! 		       && reg_base_reg[regno] == (int) REGNO (src)
  		       && reg_set_luid[regno] > reg_set_luid[REGNO (src)])
  		{
  		  rtx next = next_nonnote_insn (insn);
--- 9011,9020 ----
  				  ...
  				  (set (REGX) (plus (REGX) (CONST_INT B-A)))  */
  	      else if (GET_CODE (src) == REG
! 		       && (reg_base_reg[regno] == (int) REGNO (src)
! 			   || (GET_CODE (reg_offset[REGNO (src)]) == CONST_INT
! 			       && (reg_base_reg[regno]
! 				   == reg_base_reg[REGNO (src)]))
  		       && reg_set_luid[regno] > reg_set_luid[REGNO (src)])
  		{
  		  rtx next = next_nonnote_insn (insn);
*************** reload_cse_move2add (first)
*** 9026,9034 ****
--- 9029,9041 ----
  		      && GET_CODE (XEXP (SET_SRC (set), 1)) == CONST_INT)
  		    {
  		      rtx src3 = XEXP (SET_SRC (set), 1);
+ 		      rtx src_offset = 
+ 			(reg_base_reg[regno] == (int) REGNO (src)
+ 			 ? const0_rtx : reg_offset[REGNO (src)])
  		      rtx new_src
  			= gen_mode_int (GET_MODE (reg),
  					INTVAL (src3)
+ 					+ INTVAL (src_offset)
  					- INTVAL (reg_offset[regno]));
  		      int success = 0;
  
*************** move2add_note_store (dst, set, data)
*** 9147,9160 ****
  
  	    if (GET_CODE (src0) == REG)
  	      {
! 		if (REGNO (src0) != regno
! 		    || reg_offset[regno] != const0_rtx)
  		  {
! 		    reg_base_reg[regno] = REGNO (src0);
! 		    reg_set_luid[regno] = move2add_luid;
  		  }
  
! 		reg_offset[regno] = XEXP (src, 1);
  		break;
  	      }
  
--- 9154,9171 ----
  
  	    if (GET_CODE (src0) == REG)
  	      {
! 		int srcno = REGNO (src0);
! 		rtx offset = XEXP (src, 1);
! 
! 		if (GET_CODE (reg_offset[srcno]) == CONST_INT)
  		  {
! 		    offset = plus_constant (offset, INTVAL (reg_offset[srcno]));
! 		    srcno = reg_base_reg[srcno];
  		  }
  
! 		reg_base_reg[regno] = srcno;
! 		reg_offset[regno] = offset;
! 		reg_set_luid[regno] = move2add_luid;
  		break;
  	      }