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* [Bug tree-optimization/34160] New: Useful loop invariant motion missing
@ 2007-11-20 12:05 amonakov at gmail dot com
2007-11-20 12:06 ` [Bug tree-optimization/34160] " amonakov at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: amonakov at gmail dot com @ 2007-11-20 12:05 UTC (permalink / raw)
To: gcc-bugs
int main()
{
static int i, n;
static double a[200], b[200];
... (more variables and control flow)
for (i = 0; i < n; i++)
a[i] = b[i];
...
}
Tree-level optimisations do not pull out loads of i and n and store to i out of
loop. As a result, GCC generates five memory accesses on ia64 for each
iteration (4.3.0 20071112):
.L9:
.mii
nop 0
sxt4 r14 = r16
nop 0
.mmi
ld4 r15 = [r32]
ld4 r58 = [r33]
nop 0
;;
.mii
shladd r14 = r14, 3, r0
adds r16 = 1, r15
;;
add r15 = r35, r14
.mmi
add r14 = r34, r14
st4 [r32] = r16
cmp4.lt p6, p7 = r16, r58
;;
.mmi
nop 0
ldfd f6 = [r15]
nop 0
;;
.mib
stfd [r14] = f6
nop 0
(p6) br.cond.dptk .L9
On x86_64 situation is better (4.3.0 20070930), but not good:
.L13:
movslq %eax,%rdx
movq b.3894(,%rdx,8), %rax
movq %rax, x.3895(,%rdx,8)
leal 1(%rcx), %eax
cmpl %eax, %edi
movl %eax, %ecx
movl %eax, i.3912(%rip)
jg .L13
but the optimization happened on RTL level, as final_cleanup dump reads:
<bb 13>:
# MPT.140_429 = VDEF <MPT.140_645>
x[i.265] = b[i.265];
# VUSE <MPT.140_429>
i.23 = i;
i.265 = i.23 + 1;
# MPT.140_430 = VDEF <MPT.140_429>
i = i.265;
# VUSE <MPT.140_430>
n.274 = n;
if (n.274 > i.265)
goto <bb 13>;
else
goto <bb 14>;
--
Summary: Useful loop invariant motion missing
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: amonakov at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34160
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/34160] Useful loop invariant motion missing
2007-11-20 12:05 [Bug tree-optimization/34160] New: Useful loop invariant motion missing amonakov at gmail dot com
@ 2007-11-20 12:06 ` amonakov at gmail dot com
2007-11-20 15:43 ` rguenth at gcc dot gnu dot org
2009-04-03 12:28 ` rguenth at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: amonakov at gmail dot com @ 2007-11-20 12:06 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from amonakov at gmail dot com 2007-11-20 12:06 -------
Created an attachment (id=14584)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14584&action=view)
Preprocessed source
Testcase attached.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34160
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/34160] Useful loop invariant motion missing
2007-11-20 12:05 [Bug tree-optimization/34160] New: Useful loop invariant motion missing amonakov at gmail dot com
2007-11-20 12:06 ` [Bug tree-optimization/34160] " amonakov at gmail dot com
@ 2007-11-20 15:43 ` rguenth at gcc dot gnu dot org
2009-04-03 12:28 ` rguenth at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2007-11-20 15:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from rguenth at gcc dot gnu dot org 2007-11-20 15:43 -------
Alias got in the way here.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Keywords| |alias, missed-optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34160
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/34160] Useful loop invariant motion missing
2007-11-20 12:05 [Bug tree-optimization/34160] New: Useful loop invariant motion missing amonakov at gmail dot com
2007-11-20 12:06 ` [Bug tree-optimization/34160] " amonakov at gmail dot com
2007-11-20 15:43 ` rguenth at gcc dot gnu dot org
@ 2009-04-03 12:28 ` rguenth at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2009-04-03 12:28 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rguenth at gcc dot gnu dot org 2009-04-03 12:27 -------
<bb 10>:
# i.21_754 = PHI <i.21_1090(10), 0(9)>
# i.21_484 = PHI <i.21_1090(10), 0(9)>
D.4090_71 = b[i.21_754];
x[i.21_754] = D.4090_71;
D.4345_1088 = (unsigned int) i.21_484;
D.4346_1089 = D.4345_1088 + 1;
i.21_1090 = (int) D.4346_1089;
if (n.17_753 > i.21_1090)
goto <bb 10>;
else
goto <bb 11>;
seems to work with 4.4.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Known to fail| |4.3.3
Resolution| |FIXED
Target Milestone|--- |4.4.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34160
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2009-04-03 12:28 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2007-11-20 12:05 [Bug tree-optimization/34160] New: Useful loop invariant motion missing amonakov at gmail dot com
2007-11-20 12:06 ` [Bug tree-optimization/34160] " amonakov at gmail dot com
2007-11-20 15:43 ` rguenth at gcc dot gnu dot org
2009-04-03 12:28 ` rguenth at gcc dot gnu dot org
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