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* [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound
@ 2007-07-11 16:01 scovich at gmail dot com
2007-07-11 16:36 ` [Bug middle-end/32729] " scovich at gmail dot com
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: scovich at gmail dot com @ 2007-07-11 16:01 UTC (permalink / raw)
To: gcc-bugs
Consider the following functions:
// g++ -mtune=core2 -O3 -S -dp
void loop(int* dest, int* src, int count) {
for(int i=0; i < count; i++)
dest[i] = src[i];
}
void loop_few(int* dest, int* src) { loop(dest, src, 8); }
void loop_many(int* dest, int* src) { loop(dest, src, 64); }
loop() unrolls 8x, as expected. loop_few() peels completely, as expected.
However, loop_many() neither peels nor unrolls.
_Z9loop_manyPiS_:
xorl %edx, %edx # 34 *movdi_xor_rex64 [length = 2]
.L47:
movl (%rsi,%rdx,4), %eax # 11 *movsi_1/1 [length = 3]
movl %eax, (%rdi,%rdx,4) # 12 *movsi_1/2 [length = 3]
incq %rdx # 13 *adddi_1_rex64/1 [length = 3]
cmpq $64, %rdx # 15 cmpdi_1_insn_rex64/1 [length = 4]
jne .L47 # 16 *jcc_1 [length = 2]
rep ; ret # 35 return_internal_long [length = 1]
Ideally the optimizer would unroll 8x, then notice that (count%8==0) and
eliminate the partial unroll code. However, even a stock unroll would be better
than nothing.
--
Summary: Loop unrolling not performed with large constant loop
bound
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: scovich at gmail dot com
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/32729] Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
@ 2007-07-11 16:36 ` scovich at gmail dot com
2007-07-11 16:37 ` [Bug middle-end/32729] Regression: " scovich at gmail dot com
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: scovich at gmail dot com @ 2007-07-11 16:36 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from scovich at gmail dot com 2007-07-11 16:36 -------
(In reply to comment #0)
> // g++ -mtune=core2 -O3 -S -dp
Oops... that doesn't actually unroll loop() all, though it still peels
loop_few().
Adding -funroll-loops (supposedly enabled by -O3?) unrolls loop()
Adding -funroll-all-loops does nothing
Nested loops also have issues:
void nested_loop(int* dest, int* src) {
for(int i=0; i < 2; i++)
for(int j=0; j < 2; j++)
dest[4*i+j] = src[4*j+i];
}
becomes
_Z11nested_loopPiS_:
.LFB533:
xorl %edx, %edx # 39 *movdi_xor_rex64 [length = 2]
.L47:
movl (%rsi), %ecx # 13 *movsi_1/1 [length = 2]
movl %ecx, (%rdi,%rdx,4) # 14 *movsi_1/2 [length = 3]
movl 16(%rsi), %eax # 15 *movsi_1/1 [length = 3]
addq $4, %rsi # 17 *adddi_1_rex64/1 [length = 4]
movl %eax, 4(%rdi,%rdx,4) # 16 *movsi_1/2 [length = 4]
addq $4, %rdx # 18 *adddi_1_rex64/1 [length = 4]
cmpq $8, %rdx # 20 cmpdi_1_insn_rex64/1 [length = 4]
jne .L47 # 21 *jcc_1 [length = 2]
rep ; ret # 40 return_internal_long [length = 1]
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/32729] Regression: Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
2007-07-11 16:36 ` [Bug middle-end/32729] " scovich at gmail dot com
@ 2007-07-11 16:37 ` scovich at gmail dot com
2007-07-11 20:48 ` rakdver at gcc dot gnu dot org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: scovich at gmail dot com @ 2007-07-11 16:37 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from scovich at gmail dot com 2007-07-11 16:37 -------
Regression: gcc-4.1.2 outputs the expected code for all test cases
--
scovich at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Loop unrolling not performed|Regression: Loop unrolling
|with large constant loop |not performed with large
|bound |constant loop bound
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/32729] Regression: Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
2007-07-11 16:36 ` [Bug middle-end/32729] " scovich at gmail dot com
2007-07-11 16:37 ` [Bug middle-end/32729] Regression: " scovich at gmail dot com
@ 2007-07-11 20:48 ` rakdver at gcc dot gnu dot org
2007-07-11 20:56 ` rakdver at gcc dot gnu dot org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rakdver at gcc dot gnu dot org @ 2007-07-11 20:48 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rakdver at gcc dot gnu dot org 2007-07-11 20:47 -------
Something c++ specific, when compiled by gcc, the loop is unrolled just fine.
--
rakdver at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|unassigned at gcc dot gnu |rakdver at gcc dot gnu dot
|dot org |org
Status|UNCONFIRMED |ASSIGNED
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2007-07-11 20:47:54
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/32729] Regression: Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
` (2 preceding siblings ...)
2007-07-11 20:48 ` rakdver at gcc dot gnu dot org
@ 2007-07-11 20:56 ` rakdver at gcc dot gnu dot org
2007-07-12 7:36 ` [Bug rtl-optimization/32729] " rakdver at gcc dot gnu dot org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rakdver at gcc dot gnu dot org @ 2007-07-11 20:56 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from rakdver at gcc dot gnu dot org 2007-07-11 20:56 -------
The following patch fixes the problem; I am not quite sure why this check is
there.
Index: cfghooks.c
===================================================================
*** cfghooks.c (revision 126547)
--- cfghooks.c (working copy)
*************** tidy_fallthru_edges (void)
*** 838,845 ****
bool
can_duplicate_block_p (basic_block bb)
{
- edge e;
-
if (!cfg_hooks->can_duplicate_block_p)
internal_error ("%s does not support can_duplicate_block_p",
cfg_hooks->name);
--- 838,843 ----
*************** can_duplicate_block_p (basic_block bb)
*** 847,858 ****
if (bb == EXIT_BLOCK_PTR || bb == ENTRY_BLOCK_PTR)
return false;
- /* Duplicating fallthru block to exit would require adding a jump
- and splitting the real last BB. */
- e = find_edge (bb, EXIT_BLOCK_PTR);
- if (e && (e->flags & EDGE_FALLTHRU))
- return false;
-
return cfg_hooks->can_duplicate_block_p (bb);
}
--- 845,850 ----
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/32729] Regression: Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
` (3 preceding siblings ...)
2007-07-11 20:56 ` rakdver at gcc dot gnu dot org
@ 2007-07-12 7:36 ` rakdver at gcc dot gnu dot org
2007-07-12 10:24 ` rakdver at gcc dot gnu dot org
2007-07-15 20:53 ` [Bug rtl-optimization/32729] [4.3 Regression] : " pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: rakdver at gcc dot gnu dot org @ 2007-07-12 7:36 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from rakdver at gcc dot gnu dot org 2007-07-12 07:36 -------
Patch: http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01130.html
--
rakdver at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
URL| |http://gcc.gnu.org/ml/gcc-
| |patches/2007-
| |07/msg01130.html
Component|middle-end |rtl-optimization
Keywords| |patch
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/32729] Regression: Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
` (4 preceding siblings ...)
2007-07-12 7:36 ` [Bug rtl-optimization/32729] " rakdver at gcc dot gnu dot org
@ 2007-07-12 10:24 ` rakdver at gcc dot gnu dot org
2007-07-15 20:53 ` [Bug rtl-optimization/32729] [4.3 Regression] : " pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: rakdver at gcc dot gnu dot org @ 2007-07-12 10:24 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from rakdver at gcc dot gnu dot org 2007-07-12 10:24 -------
Subject: Bug 32729
Author: rakdver
Date: Thu Jul 12 10:24:19 2007
New Revision: 126576
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=126576
Log:
PR rtl-optimization/32729
* cfghooks.c (can_duplicate_block_p): Do not forbid duplicating blocks
that fallthru to exit.
Modified:
trunk/gcc/ChangeLog
trunk/gcc/cfghooks.c
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/32729] [4.3 Regression] : Loop unrolling not performed with large constant loop bound
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
` (5 preceding siblings ...)
2007-07-12 10:24 ` rakdver at gcc dot gnu dot org
@ 2007-07-15 20:53 ` pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-07-15 20:53 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from pinskia at gcc dot gnu dot org 2007-07-15 20:53 -------
Fixed.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
Summary|Regression: Loop unrolling |[4.3 Regression] : Loop
|not performed with large |unrolling not performed with
|constant loop bound |large constant loop bound
Target Milestone|--- |4.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32729
^ permalink raw reply [flat|nested] 8+ messages in thread
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-- links below jump to the message on this page --
2007-07-11 16:01 [Bug middle-end/32729] New: Loop unrolling not performed with large constant loop bound scovich at gmail dot com
2007-07-11 16:36 ` [Bug middle-end/32729] " scovich at gmail dot com
2007-07-11 16:37 ` [Bug middle-end/32729] Regression: " scovich at gmail dot com
2007-07-11 20:48 ` rakdver at gcc dot gnu dot org
2007-07-11 20:56 ` rakdver at gcc dot gnu dot org
2007-07-12 7:36 ` [Bug rtl-optimization/32729] " rakdver at gcc dot gnu dot org
2007-07-12 10:24 ` rakdver at gcc dot gnu dot org
2007-07-15 20:53 ` [Bug rtl-optimization/32729] [4.3 Regression] : " pinskia at gcc dot gnu dot org
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