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* [Bug rtl-optimization/19702] New: suboptimal multiple branch comparison code produced
@ 2005-01-30 1:53 yuri at tsoft dot com
2005-01-30 2:03 ` [Bug middle-end/19702] " pinskia at gcc dot gnu dot org
2005-01-31 14:28 ` kazu at cs dot umass dot edu
0 siblings, 2 replies; 3+ messages in thread
From: yuri at tsoft dot com @ 2005-01-30 1:53 UTC (permalink / raw)
To: gcc-bugs
When two comparisons immediately follow each other that compare same numbers but
branch twice based on 3 possible comparison outcomes actual comparison is
performed twice in asm code. One comparision suffices.
Also if second branches are strongly disadvantaged even pre-jxx mov for each
branch should be moved outside of the main body of the function.
Yuri (yuri at ONLYtsoftLOWER CASEcomMATTERS)
-- begin code --
int f(int k) {
if (k < 300)
return (10);
if (k > 300)
return (-10);
return (0);
}
int main() { f(299); }
-- end code --
obtained assembly log:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 8b 55 08 mov 0x8(%ebp),%edx
6: 81 fa 2b 01 00 00 cmp $0x12b,%edx
c: b8 0a 00 00 00 mov $0xa,%eax
11: 7e 0f jle 22 <_Z1fi+0x22>
13: 81 fa 2c 01 00 00 cmp $0x12c,%edx
19: b8 f6 ff ff ff mov $0xfffffff6,%eax
1e: 7f 02 jg 22 <_Z1fi+0x22>
20: 31 c0 xor %eax,%eax
22: c9 leave
23: c3 ret
expected assembly log:
: 55 push %ebp
: 89 e5 mov %esp,%ebp
: 8b 55 08 mov 0x8(%ebp),%edx
: 81 fa 2b 01 00 00 cmp $0x12b,%edx
: b8 0a 00 00 00 mov $0xa,%eax
: 7e 0f jle 22 <_Z1fi+ret>
: b8 f6 ff ff ff mov $0xfffffff6,%eax
: 7f 02 je 22 <_Z1fi+ret>
: 31 c0 xor %eax,%eax
ret: c9 leave
: c3 ret
--
Summary: suboptimal multiple branch comparison code produced
Product: gcc
Version: 3.4.2
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: yuri at tsoft dot com
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19702
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/19702] suboptimal multiple branch comparison code produced
2005-01-30 1:53 [Bug rtl-optimization/19702] New: suboptimal multiple branch comparison code produced yuri at tsoft dot com
@ 2005-01-30 2:03 ` pinskia at gcc dot gnu dot org
2005-01-31 14:28 ` kazu at cs dot umass dot edu
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-01-30 2:03 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-01-30 02:03 -------
Confirmed.
The problem is that fold changes "k < 300" to "k <= 299".
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Component|rtl-optimization |middle-end
Ever Confirmed| |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2005-01-30 02:03:14
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19702
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/19702] suboptimal multiple branch comparison code produced
2005-01-30 1:53 [Bug rtl-optimization/19702] New: suboptimal multiple branch comparison code produced yuri at tsoft dot com
2005-01-30 2:03 ` [Bug middle-end/19702] " pinskia at gcc dot gnu dot org
@ 2005-01-31 14:28 ` kazu at cs dot umass dot edu
1 sibling, 0 replies; 3+ messages in thread
From: kazu at cs dot umass dot edu @ 2005-01-31 14:28 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From kazu at cs dot umass dot edu 2005-01-31 14:28 -------
*** This bug has been marked as a duplicate of 14483 ***
--
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |DUPLICATE
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19702
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2005-01-31 14:28 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2005-01-30 1:53 [Bug rtl-optimization/19702] New: suboptimal multiple branch comparison code produced yuri at tsoft dot com
2005-01-30 2:03 ` [Bug middle-end/19702] " pinskia at gcc dot gnu dot org
2005-01-31 14:28 ` kazu at cs dot umass dot edu
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