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From: "amodra at bigpond dot net dot au" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/16800] PowerPC - Unnecessary rldicl Date: Wed, 24 Nov 2004 07:00:00 -0000 [thread overview] Message-ID: <20041124070017.9553.qmail@sourceware.org> (raw) In-Reply-To: <20040728170038.16800.steinmtz@us.ibm.com> ------- Additional Comments From amodra at bigpond dot net dot au 2004-11-24 07:00 ------- I believe this problem is caused by rs6000_rtx_costs. The two following insns are successfully combined: (insn 20 19 21 0 (set (reg:DI 126) (eq:DI (reg:CCFP 125) (const_int 0 [0x0]))) 410 {*rs6000.md:11408} (insn_list:REG_DEP_TRUE 19 (nil)) (expr_list:REG_DEAD (reg:CCFP 125) (nil))) (insn 21 20 22 0 (set (reg:SI 124) (subreg:SI (reg:DI 126) 4)) 280 {*movsi_internal1} (insn_list:REG_DEP_TRUE 20 (nil)) (expr_list:REG_DEAD (reg:DI 126) (nil))) to (insn 21 20 22 0 (set (reg:SI 124) (eq:SI (reg:CCFP 125) (const_int 0 [0x0]))) 409 {*rs6000.md:11376} (insn_list:REG_DEP_TRUE 20 (nil)) (expr_list:REG_DEAD (reg:DI 126) (nil))) Following that, the new insn 21 and (insn 22 21 23 0 (set (reg:DI 121) (zero_extend:DI (reg:SI 124))) 24 {*rs6000.md:379} (insn_list:REG_DEP_TRUE 21 (nil)) (expr_list:REG_DEAD (reg:SI 124) (nil))) is a combine candidate, with a good result pattern of (set (reg:DI 121) (eq:DI (reg:CCFP 125) (const_int 0 [0x0]))) However, rs6000_rtx_costs decides this patten is more expensive than the previous two instructions. rejecting combination of insns 21 and 22 original costs 12 + 4 = 16 replacement cost 20 Code in question is as follows. I don't understand why these particular comparisons have been singled out, or why the mode == Pmode test. This contributes 12 case EQ: case GTU: case LTU: if (mode == Pmode) { switch (outer_code) { case SET: *total = COSTS_N_INSNS (3); break; The (const_int 0) contributes 8! This is because outer_code is EQ, which doesn't match anything in the rather long set of outer_code tests for CONST_INT. An obvious fix is to handle EQ and other comparisons here. -- What |Removed |Added ---------------------------------------------------------------------------- CC| |dje at gcc dot gnu dot org Last reconfirmed|2004-08-02 01:02:22 |2004-11-24 07:00:16 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16800
next prev parent reply other threads:[~2004-11-24 7:00 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2004-07-28 17:01 [Bug other/16800] New: " gcc-bugzilla at gcc dot gnu dot org 2004-07-28 17:39 ` [Bug target/16800] " bangerth at dealii dot org 2004-08-02 1:02 ` pinskia at gcc dot gnu dot org 2004-11-01 0:27 ` pinskia at gcc dot gnu dot org 2004-11-22 22:28 ` steinmtz at us dot ibm dot com 2004-11-24 7:00 ` amodra at bigpond dot net dot au [this message] 2004-11-24 9:41 ` amodra at bigpond dot net dot au 2004-11-24 15:22 ` dje at watson dot ibm dot com 2004-11-27 23:01 ` cvs-commit at gcc dot gnu dot org 2004-11-28 0:07 ` pinskia at gcc dot gnu dot org
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