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From: "steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/43597] Move and compare with 0 can be combined Date: Wed, 31 Mar 2010 14:59:00 -0000 [thread overview] Message-ID: <20100331145910.21175.qmail@sourceware.org> (raw) In-Reply-To: <bug-43597-17659@http.gcc.gnu.org/bugzilla/> ------- Comment #2 from steven at gcc dot gnu dot org 2010-03-31 14:59 ------- In .final, the insns look like this: @(insn:TI 9 7 8 t.c:8 (set (reg:CC 24 cc) @ (compare:CC (reg:SI 0 r0 [orig:134 f ] [134]) @ (const_int 0 [0x0]))) 220 {*arm_cmpsi_insn} (expr_list:REG_DEAD (reg:SI 0 r0 [orig:134 f ] [134]) @ (nil))) cmp r0, #0 @ 9 *arm_cmpsi_insn/1 [length = 4] @(insn 8 9 10 t.c:7 (set (reg/v:SI 5 r5 [orig:134 f ] [134]) @ (reg:SI 0 r0)) 658 {*thumb2_movsi_insn} (nil)) mov r5, r0 @ 8 *thumb2_movsi_insn/1 [length = 4] This, AFAICT, would match with the pattern and constraints of movsi_compare0: ;; If copying one reg to another we can set the condition codes according to ;; its value. Such a move is common after a return from subroutine and the ;; result is being tested against zero. (define_insn "*movsi_compare0" [(set (reg:CC CC_REGNUM) (compare:CC (match_operand:SI 1 "s_register_operand" "0,r") (const_int 0))) (set (match_operand:SI 0 "s_register_operand" "=r,r") (match_dup 1))] "TARGET_32BIT" "@ cmp%?\\t%0, #0 sub%.\\t%0, %1, #0" [(set_attr "conds" "set")] ) But this insns can probably only be formed in the .combine pass, since (to the best of my knowledge) we don't construct multiple-set insns in any other pass. In the .combine pass, the two insns look like this (obviously reversed, as you could already suspect from the insns numbers 9 and 8 above): (insn 8 7 9 2 t.c:7 (set (reg/v:SI 134 [ f ]) (reg:SI 0 r0)) 658 {*thumb2_movsi_insn} (expr_list:REG_DEAD (reg:SI 0 r0) (nil))) (insn 9 8 10 2 t.c:8 (set (reg:CC 24 cc) (compare:CC (reg/v:SI 134 [ f ]) (const_int 0 [0x0]))) 220 {*arm_cmpsi_insn} (nil)) But combine does not even try to combine these two insns: ------------ ... insn_cost 24: 0 Trying 9 -> 10: Failed to match this instruction: (set (pc) (if_then_else (lt (reg/v:SI 134 [ f ]) (const_int 0 [0x0])) (label_ref:SI 29) (pc))) foo4 ... ------------ -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43597
next prev parent reply other threads:[~2010-03-31 14:59 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-03-31 7:50 [Bug target/43597] New: " carrot at google dot com 2010-03-31 7:51 ` [Bug target/43597] " carrot at google dot com 2010-03-31 9:01 ` steven at gcc dot gnu dot org 2010-03-31 9:08 ` ramana at gcc dot gnu dot org 2010-03-31 14:59 ` steven at gcc dot gnu dot org [this message] 2010-03-31 15:16 ` steven at gcc dot gnu dot org 2010-03-31 22:50 ` steven at gcc dot gnu dot org 2010-03-31 22:51 ` steven at gcc dot gnu dot org 2010-04-17 17:15 ` rearnsha at gcc dot gnu dot org 2010-04-22 12:26 ` carrot at google dot com [not found] <bug-43597-4@http.gcc.gnu.org/bugzilla/> 2011-08-17 11:45 ` vries at gcc dot gnu.org 2011-08-17 13:05 ` vries at gcc dot gnu.org
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