------- 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
