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* [Bug target/18154] New: Inefficient max/min code for PowerPC
@ 2004-10-26 4:18 dje at gcc dot gnu dot org
2004-10-26 4:25 ` [Bug target/18154] " pinskia at gcc dot gnu dot org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: dje at gcc dot gnu dot org @ 2004-10-26 4:18 UTC (permalink / raw)
To: gcc-bugs
int min(int a, int b) {
if (a < b)
return a;
else
return b;
}
should produce
rlwinm r2,r3,1,31,31
subfc r0,r4,r3
rlwinm r0,r4,1,31,31
subfe r0,r2,r0
andc r2,r4,r0
and r0,r3,r0
or r3,r0,r2
blr
but instead produces a branch sequence
mr r0,r3
mr r3,r4
cmpw cr7,r0,r4
bgelr- cr7
mr r3,r0
blr
with unnecessary dependencies.
--
Summary: Inefficient max/min code for PowerPC
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dje at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: *-*-*
GCC host triplet: powerpc-*-*
GCC target triplet: *-*-*
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
@ 2004-10-26 4:25 ` pinskia at gcc dot gnu dot org
2004-10-26 20:06 ` dje at gcc dot gnu dot org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-10-26 4:25 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-10-26 04:25 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed| |1
Last reconfirmed|0000-00-00 00:00:00 |2004-10-26 04:25:17
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
2004-10-26 4:25 ` [Bug target/18154] " pinskia at gcc dot gnu dot org
@ 2004-10-26 20:06 ` dje at gcc dot gnu dot org
2004-10-26 21:25 ` dje at gcc dot gnu dot org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: dje at gcc dot gnu dot org @ 2004-10-26 20:06 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From dje at gcc dot gnu dot org 2004-10-26 20:06 -------
XLC chooses the straight-line code sequence versus compare and branch based on
a cost model. This should not be a uniform change in behavior for PowerPC.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
2004-10-26 4:25 ` [Bug target/18154] " pinskia at gcc dot gnu dot org
2004-10-26 20:06 ` dje at gcc dot gnu dot org
@ 2004-10-26 21:25 ` dje at gcc dot gnu dot org
2004-10-27 23:45 ` geoffk at gcc dot gnu dot org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: dje at gcc dot gnu dot org @ 2004-10-26 21:25 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From dje at gcc dot gnu dot org 2004-10-26 21:25 -------
Also, do not enable when optimizing for size.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
` (2 preceding siblings ...)
2004-10-26 21:25 ` dje at gcc dot gnu dot org
@ 2004-10-27 23:45 ` geoffk at gcc dot gnu dot org
2004-10-27 23:52 ` pinskia at gcc dot gnu dot org
2005-04-24 14:31 ` pinskia at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: geoffk at gcc dot gnu dot org @ 2004-10-27 23:45 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From geoffk at gcc dot gnu dot org 2004-10-27 23:45 -------
I'm not sure that subfc/subfe is going to be cheaper than a compare and a branch, even if the branch is
mispredicted half the time. Do you have timing results?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
` (3 preceding siblings ...)
2004-10-27 23:45 ` geoffk at gcc dot gnu dot org
@ 2004-10-27 23:52 ` pinskia at gcc dot gnu dot org
2005-04-24 14:31 ` pinskia at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-10-27 23:52 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-10-27 23:52 -------
I should note when I was doing SPEC work, using subfc/subfe did not help SPEC at all (I tried to change
the source and also rs6000.md).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/18154] Inefficient max/min code for PowerPC
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
` (4 preceding siblings ...)
2004-10-27 23:52 ` pinskia at gcc dot gnu dot org
@ 2005-04-24 14:31 ` pinskia at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-04-24 14:31 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-04-24 14:31 -------
On the mainline, we now produce:
cmpw cr7,r3,r4
blelr- cr7
mr r3,r4
blr
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2005-04-24 14:31 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2004-10-26 4:18 [Bug target/18154] New: Inefficient max/min code for PowerPC dje at gcc dot gnu dot org
2004-10-26 4:25 ` [Bug target/18154] " pinskia at gcc dot gnu dot org
2004-10-26 20:06 ` dje at gcc dot gnu dot org
2004-10-26 21:25 ` dje at gcc dot gnu dot org
2004-10-27 23:45 ` geoffk at gcc dot gnu dot org
2004-10-27 23:52 ` pinskia at gcc dot gnu dot org
2005-04-24 14:31 ` pinskia at gcc dot gnu dot org
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