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* [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code
@ 2005-10-28 16:15 tobi at gcc dot gnu dot org
2005-10-28 18:01 ` [Bug tree-optimization/24568] " pinskia at gcc dot gnu dot org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: tobi at gcc dot gnu dot org @ 2005-10-28 16:15 UTC (permalink / raw)
To: gcc-bugs
xgcc (GCC) 4.1.0 20051020 (experimental)
can't optimize the following code (from <http://thedailywtf.com>):
int convertToMinutes(long milliDiff)
{
int negative = 0;
int minutesDiff = -1;
if (milliDiff < 0)
{
negative = 1;
milliDiff = -milliDiff; // Make positive (is easier)
}
if (milliDiff == 0) // Watch out for exceptional value 0
minutesDiff = 0;
else
minutesDiff = (int) (milliDiff / 1000) / 60;
if (negative) minutesDiff = -minutesDiff; // Make it negative again
return minutesDiff;
}
The code should simplify to
int convertToMinutes (long i)
{
return i / 60000;
}
But the final tree dump contains the complete logic even in the case of high
optimization levels.
An interesting peculiarity from the assembly:
.file "milli.c"
.text
.p2align 4,,15
.globl convertToMinutes
.type convertToMinutes, @function
convertToMinutes:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl %esi, 4(%esp)
movl 8(%ebp), %esi
movl %ebx, (%esp)
xorl %ebx, %ebx
testl %esi, %esi
js .L12 ;;;;; jump from here
.L4:
xorl %ecx, %ecx
testl %esi, %esi
je .L7
movl $1172812403, %eax
imull %esi
movl %esi, %eax
sarl $31, %eax
movl %edx, %ecx
sarl $14, %ecx
subl %eax, %ecx
.L7:
testl %ebx, %ebx
je .L8
negl %ecx
.L8:
movl (%esp), %ebx
movl %ecx, %eax
movl 4(%esp), %esi
movl %ebp, %esp
popl %ebp
ret
.p2align 4,,7
.L12: ;;;;;;;;;;; all the way down here, probably out of the prefetch buffer
negl %esi
movl $1, %ebx
jmp .L4
.size convertToMinutes, .-convertToMinutes
.ident "GCC: (GNU) 4.1.0 20051020 (experimental)"
.section .note.GNU-stack,"",@progbits
--
Summary: Missed optimization: trivialization of silly code
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: tobi at gcc dot gnu dot org
GCC target triplet: i686-pc-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
@ 2005-10-28 18:01 ` pinskia at gcc dot gnu dot org
2005-10-28 18:06 ` pinskia at gcc dot gnu dot org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:01 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gcc dot gnu dot org 2005-10-28 18:01 -------
There is a couple of different bugs in the is code snipit really. Let me file
new bugs for each of them.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
2005-10-28 18:01 ` [Bug tree-optimization/24568] " pinskia at gcc dot gnu dot org
@ 2005-10-28 18:06 ` pinskia at gcc dot gnu dot org
2005-10-28 18:10 ` pinskia at gcc dot gnu dot org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:06 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pinskia at gcc dot gnu dot org 2005-10-28 18:05 -------
(In reply to comment #1)
> There is a couple of different bugs in the is code snipit really. Let me file
> new bugs for each of them.
PR 24574 is the first issue which seems like it could happen in really code
(though not as much as one thinks).
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |24574
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
2005-10-28 18:01 ` [Bug tree-optimization/24568] " pinskia at gcc dot gnu dot org
2005-10-28 18:06 ` pinskia at gcc dot gnu dot org
@ 2005-10-28 18:10 ` pinskia at gcc dot gnu dot org
2005-10-28 18:11 ` pinskia at gcc dot gnu dot org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:10 UTC (permalink / raw)
To: gcc-bugs
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (2 preceding siblings ...)
2005-10-28 18:10 ` pinskia at gcc dot gnu dot org
@ 2005-10-28 18:11 ` pinskia at gcc dot gnu dot org
2005-10-28 18:15 ` pinskia at gcc dot gnu dot org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:11 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from pinskia at gcc dot gnu dot org 2005-10-28 18:11 -------
(In reply to comment #2)
> PR 24574 is the first issue which seems like it could happen in really code
> (though not as much as one thinks).
That was for the inner if.
I have to see how to reduce the outer ones.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (3 preceding siblings ...)
2005-10-28 18:11 ` pinskia at gcc dot gnu dot org
@ 2005-10-28 18:15 ` pinskia at gcc dot gnu dot org
2005-10-28 18:18 ` pinskia at gcc dot gnu dot org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:15 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from pinskia at gcc dot gnu dot org 2005-10-28 18:15 -------
Another issue is PR 24575:
-(-a/10) is not converted into a/10.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |24575
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (4 preceding siblings ...)
2005-10-28 18:15 ` pinskia at gcc dot gnu dot org
@ 2005-10-28 18:18 ` pinskia at gcc dot gnu dot org
2005-10-28 18:20 ` [Bug tree-optimization/24568] [meta-bugs] " pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:18 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from pinskia at gcc dot gnu dot org 2005-10-28 18:18 -------
Last but not least is:
int f(int i)
{
if (i < 0) return i/10;
return i/10;
}
int f2(int i)
{
return i/10;
}
Which is converted at the rtl level but not at the tree level (I think there is
a bug about this already).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] [meta-bugs] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (5 preceding siblings ...)
2005-10-28 18:18 ` pinskia at gcc dot gnu dot org
@ 2005-10-28 18:20 ` pinskia at gcc dot gnu dot org
2005-10-28 18:21 ` pinskia at gcc dot gnu dot org
2007-03-29 12:29 ` [Bug tree-optimization/24568] [meta-bug] " steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:20 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from pinskia at gcc dot gnu dot org 2005-10-28 18:19 -------
Confirmed, I am changing this into a meta-bug because there are three different
issues that this bug depends on now.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2005-10-28 18:19:55
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] [meta-bugs] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (6 preceding siblings ...)
2005-10-28 18:20 ` [Bug tree-optimization/24568] [meta-bugs] " pinskia at gcc dot gnu dot org
@ 2005-10-28 18:21 ` pinskia at gcc dot gnu dot org
2007-03-29 12:29 ` [Bug tree-optimization/24568] [meta-bug] " steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-10-28 18:21 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from pinskia at gcc dot gnu dot org 2005-10-28 18:21 -------
Oh, for PR 24575 to do anything useful in this case, we need to a tree based
combiner.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |15459
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/24568] [meta-bug] Missed optimization: trivialization of silly code
2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
` (7 preceding siblings ...)
2005-10-28 18:21 ` pinskia at gcc dot gnu dot org
@ 2007-03-29 12:29 ` steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: steven at gcc dot gnu dot org @ 2007-03-29 12:29 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from steven at gcc dot gnu dot org 2007-03-29 13:29 -------
For the original test case, our current output before expand (i.e. the
final_cleanup dump) on hosts where sizeof(long)==sizeof(int) is this:
;; Function convertToMinutes (convertToMinutes)
convertToMinutes (milliDiff)
{
int minutesDiff.24;
int minutesDiff;
<bb 2>:
if (milliDiff < 0) goto <L0>; else goto <L1>;
<L0>:;
minutesDiff = -milliDiff / 60000;
minutesDiff.24 = -minutesDiff;
goto <bb 7> (<L6>);
<L1>:;
if (milliDiff == 0) goto <L13>; else goto <L3>;
<L13>:;
minutesDiff.24 = 0;
goto <bb 7> (<L6>);
Invalid sum of outgoing probabilities 0.0%
Invalid sum of incoming frequencies 2000, should be 0
<L3>:;
minutesDiff.24 = milliDiff / 60000;
Invalid sum of incoming frequencies 8000, should be 10000
<L6>:;
return minutesDiff.24;
}
Note that on hosts where sizeof(long) != sizeof(int), you can't optimize the
original test case to i/60000.
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2006-02-26 19:10:03 |2007-03-29 13:29:35
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24568
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2007-03-29 12:29 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
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2005-10-28 16:15 [Bug tree-optimization/24568] New: Missed optimization: trivialization of silly code tobi at gcc dot gnu dot org
2005-10-28 18:01 ` [Bug tree-optimization/24568] " pinskia at gcc dot gnu dot org
2005-10-28 18:06 ` pinskia at gcc dot gnu dot org
2005-10-28 18:10 ` pinskia at gcc dot gnu dot org
2005-10-28 18:11 ` pinskia at gcc dot gnu dot org
2005-10-28 18:15 ` pinskia at gcc dot gnu dot org
2005-10-28 18:18 ` pinskia at gcc dot gnu dot org
2005-10-28 18:20 ` [Bug tree-optimization/24568] [meta-bugs] " pinskia at gcc dot gnu dot org
2005-10-28 18:21 ` pinskia at gcc dot gnu dot org
2007-03-29 12:29 ` [Bug tree-optimization/24568] [meta-bug] " steven at gcc dot gnu dot org
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