[3.0] Re: egcs/gcc ChangeLog config/i386/i386.md

[Richard Henderson]

On Thu, Oct 04, 2001 at 02:20:39PM -0000, hubicka@gcc.gnu.org wrote:
> 	* i386.c (setcc peep2): Do not use clobber of flags.

This severely pessimizes the PII core.

The "xor reg,reg" is special in that it sets a "register clear"
flag that avoids a partial register stall with the subsequent
setcc.  Unfortunately, "mov $0,reg" does not have the same effect.

I think the following is in order.  Bootstrapped on i686-linux
with -march=k6 in BOOT_CFLAGS.

Ok, Mark?


r~


	* i386.md (movsi_xor): Export.
	(setcc peep2): Use it when available.

Index: i386.md
===================================================================
RCS file: /cvs/gcc/gcc/gcc/config/i386/i386.md,v
retrieving revision 1.204.2.17
diff -c -p -d -r1.204.2.17 i386.md
*** i386.md	2001/10/04 14:20:33	1.204.2.17
--- i386.md	2001/10/05 18:08:47
***************
*** 1581,1587 ****
    [(set_attr "type" "pop")
     (set_attr "mode" "SI")])
  
! (define_insn "*movsi_xor"
    [(set (match_operand:SI 0 "register_operand" "=r")
  	(match_operand:SI 1 "const0_operand" "i"))
     (clobber (reg:CC 17))]
--- 1581,1587 ----
    [(set_attr "type" "pop")
     (set_attr "mode" "SI")])
  
! (define_insn "movsi_xor"
    [(set (match_operand:SI 0 "register_operand" "=r")
  	(match_operand:SI 1 "const0_operand" "i"))
     (clobber (reg:CC 17))]
***************
*** 9606,9617 ****
  	(zero_extend (match_dup 1)))]
    "peep2_reg_dead_p (3, operands[1])
     && ! reg_overlap_mentioned_p (operands[3], operands[0])"
!   [(set (match_dup 3) (const_int 0))
!    (set (match_dup 4) (match_dup 0))
     (set (strict_low_part (match_dup 5))
  	(match_dup 2))]
!   "operands[4] = gen_rtx_REG (GET_MODE (operands[0]), 17);
!    operands[5] = gen_rtx_REG (QImode, REGNO (operands[3]));")
  
  ;; Call instructions.
  
--- 9606,9623 ----
  	(zero_extend (match_dup 1)))]
    "peep2_reg_dead_p (3, operands[1])
     && ! reg_overlap_mentioned_p (operands[3], operands[0])"
!   [(set (match_dup 4) (match_dup 0))
     (set (strict_low_part (match_dup 5))
  	(match_dup 2))]
!   "
! {
!   operands[4] = gen_rtx_REG (GET_MODE (operands[0]), 17);
!   operands[5] = gen_rtx_REG (QImode, REGNO (operands[3]));
!   if (HAVE_movsi_xor)
!     emit_insn (gen_movsi_xor (operands[3], const0_rtx));
!   else
!     emit_insn (gen_movsi (operands[3], const0_rtx));
! }")
  
  ;; Call instructions.