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* [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load
@ 2014-08-04 0:22 vries at gcc dot gnu.org
2014-08-04 10:05 ` [Bug rtl-optimization/62004] " rguenth at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-04 0:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
Bug ID: 62004
Summary: dead type-unsafe load replaces type-safe load
Product: gcc
Version: 4.8.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Created attachment 33230
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33230&action=edit
test-case
I've tried to write a program in which there is a type-unsafe load, which is
never executed, to see if tail-merge would fail. In other words, I've tried to
come up with a 'load' variant of PR61964.
With attached test-case load-4.c and current 4.8 branch, I get the following
results:
...
$ gcc -O2 load-4.c; ./a.out ; echo $?
1
...
Adding -fno-strict-aliasing allows the test to pass:
...
$ gcc -O2 load-4.c -fno-strict-aliasing ; ./a.out ; echo $?
0
...
However AFAICT, the test-case is correct, in the sense that the only
type-unsafe code is dead, so -fno-strict-aliasing should not be necessary to
allow the test to pass.
My intention was to trigger a a problem in tail-merge. However, skipping
tail-merge still doesn't make the test pass:
...
$ gcc -O2 load-4.c -fstrict-aliasing -fno-tree-tail-merge; ./a.out ; echo $?
1
...
At rtl level, the same type of optimization as tail-merge is done. We start out
with the if-then-else-join before expand:
...
if (_13 == h_10)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
p_14 = MEM[(struct head *)_13].first;
goto <bb 5>;
<bb 4>:
p_15 = _13->next;
<bb 5>:
...
And this is expanded into rtl:
...
(jump_insn 23 22 24 2 (set (pc)
(if_then_else (ne (reg:CCZ 17 flags)
(const_int 0 [0]))
(label_ref 28)
(pc))) load-4.c:44 -1
(expr_list:REG_BR_PROB (const_int 8986 [0x231a])
(nil))
-> 28)
(note 24 23 25 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
(insn 25 24 26 4 (set (reg/v/f:DI 59 [ p ])
(mem/f:DI (reg/f:DI 66 [ D.1751 ]) [4 MEM[(struct head *)_13].first+0
S8 A64])) load-4.c:46 -1
(nil))
(jump_insn 26 25 27 4 (set (pc)
(label_ref 31)) -1
(nil)
-> 31)
(barrier 27 26 28)
(code_label 28 27 29 5 2 "" [1 uses])
(note 29 28 30 5 [bb 5] NOTE_INSN_BASIC_BLOCK)
(insn 30 29 31 5 (set (reg/v/f:DI 59 [ p ])
(mem/f:DI (reg/f:DI 66 [ D.1751 ]) [4 _13->next+0 S8 A64])) load-4.c:49
-1
(nil))
(code_label 31 30 32 6 3 "" [1 uses])
...
Already at into_cfglayout, the jump 26 is removed, causing the 'dead' bb4 to
become alive:
...
try_optimize_cfg iteration 1
Removing jump 26.
<SNIP>
(jump_insn 23 22 24 2 (set (pc)
(if_then_else (ne (reg:CCZ 17 flags)
(const_int 0 [0]))
(label_ref 28)
(pc))) load-4.c:44 612 {*jcc_1}
(expr_list:REG_BR_PROB (const_int 8986 [0x231a])
(nil))
-> 28)
(note 24 23 25 3 [bb 3] NOTE_INSN_BASIC_BLOCK)
(insn 25 24 28 3 (set (reg/v/f:DI 59 [ p ])
(mem/f:DI (reg/f:DI 66 [ D.1751 ]) [4 MEM[(struct head *)_13].first+0
S8 A64])) load-4.c:46 87 {*movdi_internal_rex64}
(nil))
(code_label 28 25 29 4 2 "" [1 uses])
(note 29 28 30 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
(insn 30 29 31 4 (set (reg/v/f:DI 59 [ p ])
(mem/f:DI (reg/f:DI 66 [ D.1751 ]) [4 _13->next+0 S8 A64])) load-4.c:49
87 {*movdi_internal_rex64}
(nil))
...
And after ce1, we're just left with the code from bb4:
...
IF-THEN-ELSE-JOIN block found, pass 1, test 2, then 3, else 4, join 5
changing bb of uid 30
from 4 to 2
deleting insn with uid = 29.
deleting insn with uid = 28.
deleting block 4
Removing jump 23.
<SNIP>
(insn 30 22 33 2 (set (reg/v/f:DI 59 [ p ])
(mem/f:DI (reg/f:DI 66 [ D.1751 ]) [4 _13->next+0 S8 A64])) load-4.c:49
87 {*movdi_internal_rex64}
(expr_list:REG_DEAD (reg/f:DI 66 [ D.1751 ])
(nil)))
...
Using -fno-if-conversion allows the test to pass:
...
$ gcc -O2 load-4.c -fstrict-aliasing -fno-tree-tail-merge -fno-if-conversion;
./a.out ; echo $?
0
...
And indeed, the problem also triggers for tail-merge:
...
$ gcc.sh -O2 load-4.c -fstrict-aliasing -ftree-tail-merge -fno-if-conversion;
./a.out ; echo $?
1
...
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
@ 2014-08-04 10:05 ` rguenth at gcc dot gnu.org
2014-08-04 14:54 ` vries at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-08-04 10:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Status|UNCONFIRMED |NEW
Last reconfirmed| |2014-08-04
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Heh, interesting set of events ;)
Now it is interesting how much we desire to perform the tail-merging - we
_could_
change the alias sets of loads (and stores...) to a "common" one (either if
they
are "equal" or just zero otherwise). Depends on how much we like this kind
of pessimization.
Same for the RTL bits of course.
Btw, I still see the conditional execution after RTL expansion, just
cfglayout mode doesn't have unconditonal gotos for the edges.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
2014-08-04 10:05 ` [Bug rtl-optimization/62004] " rguenth at gcc dot gnu.org
@ 2014-08-04 14:54 ` vries at gcc dot gnu.org
2014-08-06 7:06 ` pinskia at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-04 14:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
--- Comment #2 from vries at gcc dot gnu.org ---
Created attachment 33242
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33242&action=edit
patch to fix if-conversion
(In reply to Richard Biener from comment #1)
> Heh, interesting set of events ;)
>
> Now it is interesting how much we desire to perform the tail-merging - we
> _could_
> change the alias sets of loads (and stores...) to a "common" one (either if
> they
> are "equal" or just zero otherwise). Depends on how much we like this kind
> of pessimization.
>
> Same for the RTL bits of course.
>
> Btw, I still see the conditional execution after RTL expansion, just
> cfglayout mode doesn't have unconditonal gotos for the edges.
Right, when doing fdump-rtl-all, it looks like fallthrough, but it isn't, I
forgot. So it's just if-conversion that does the wrong thing.
Attached patch fixes 4.8 if-conversion in a conservative way (I suppose we want
a conservative fix for 4.8 and 4.9). OK for testing?
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
2014-08-04 10:05 ` [Bug rtl-optimization/62004] " rguenth at gcc dot gnu.org
2014-08-04 14:54 ` vries at gcc dot gnu.org
@ 2014-08-06 7:06 ` pinskia at gcc dot gnu.org
2014-08-08 11:41 ` vries at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2014-08-06 7:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> Heh, interesting set of events ;)
I have a store version that fires on mips64 with a modified testcase too, see
bug 62030.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
` (2 preceding siblings ...)
2014-08-06 7:06 ` pinskia at gcc dot gnu.org
@ 2014-08-08 11:41 ` vries at gcc dot gnu.org
2014-08-15 21:24 ` vries at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-08 11:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
vries at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
` (3 preceding siblings ...)
2014-08-08 11:41 ` vries at gcc dot gnu.org
@ 2014-08-15 21:24 ` vries at gcc dot gnu.org
2014-08-16 17:38 ` vries at gcc dot gnu.org
2014-08-18 8:51 ` [Bug rtl-optimization/62004] [if-conversion] " vries at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-15 21:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
--- Comment #6 from vries at gcc dot gnu.org ---
Author: vries
Date: Fri Aug 15 21:23:21 2014
New Revision: 214044
URL: https://gcc.gnu.org/viewcvs?rev=214044&root=gcc&view=rev
Log:
Fix if-conversion pass for dead type-unsafe code
2014-08-15 Tom de Vries <tom@codesourcery.com>
Backport from mainline:
2014-08-14 Tom de Vries <tom@codesourcery.com>
PR rtl-optimization/62004
PR rtl-optimization/62030
* ifcvt.c (rtx_interchangeable_p): New function.
(noce_try_move, noce_process_if_block): Use rtx_interchangeable_p.
* gcc.dg/pr62004.c: New test.
* gcc.dg/pr62030.c: Same.
* gcc.target/mips/pr62030-octeon.c: Same.
2014-08-05 Richard Biener <rguenther@suse.de>
* emit-rtl.h (mem_attrs_eq_p): Declare.
* emit-rtl.c (mem_attrs_eq_p): Export.
Added:
branches/gcc-4_9-branch/gcc/testsuite/gcc.dg/pr62004.c
branches/gcc-4_9-branch/gcc/testsuite/gcc.dg/pr62030.c
branches/gcc-4_9-branch/gcc/testsuite/gcc.target/mips/pr62030-octeon.c
Modified:
branches/gcc-4_9-branch/gcc/ChangeLog
branches/gcc-4_9-branch/gcc/emit-rtl.c
branches/gcc-4_9-branch/gcc/emit-rtl.h
branches/gcc-4_9-branch/gcc/ifcvt.c
branches/gcc-4_9-branch/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
` (4 preceding siblings ...)
2014-08-15 21:24 ` vries at gcc dot gnu.org
@ 2014-08-16 17:38 ` vries at gcc dot gnu.org
2014-08-18 8:51 ` [Bug rtl-optimization/62004] [if-conversion] " vries at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-16 17:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
--- Comment #7 from vries at gcc dot gnu.org ---
Author: vries
Date: Sat Aug 16 17:38:04 2014
New Revision: 214067
URL: https://gcc.gnu.org/viewcvs?rev=214067&root=gcc&view=rev
Log:
Fix if-conversion pass for dead type-unsafe code
2014-08-15 Tom de Vries <tom@codesourcery.com>
Backport from mainline:
2014-08-14 Tom de Vries <tom@codesourcery.com>
PR rtl-optimization/62004
PR rtl-optimization/62030
* ifcvt.c (rtx_interchangeable_p): New function.
(noce_try_move, noce_process_if_block): Use rtx_interchangeable_p.
* gcc.dg/pr62004.c: New test.
* gcc.dg/pr62030.c: Same.
* gcc.target/mips/pr62030-octeon.c: Same.
2014-08-05 Richard Biener <rguenther@suse.de>
* emit-rtl.h (mem_attrs_eq_p): Declare.
* emit-rtl.c (mem_attrs_eq_p): Export.
Added:
branches/gcc-4_8-branch/gcc/testsuite/gcc.dg/pr62004.c
branches/gcc-4_8-branch/gcc/testsuite/gcc.dg/pr62030.c
branches/gcc-4_8-branch/gcc/testsuite/gcc.target/mips/pr62030-octeon.c
Modified:
branches/gcc-4_8-branch/gcc/ChangeLog
branches/gcc-4_8-branch/gcc/emit-rtl.c
branches/gcc-4_8-branch/gcc/emit-rtl.h
branches/gcc-4_8-branch/gcc/ifcvt.c
branches/gcc-4_8-branch/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/62004] [if-conversion] dead type-unsafe load replaces type-safe load
2014-08-04 0:22 [Bug rtl-optimization/62004] New: dead type-unsafe load replaces type-safe load vries at gcc dot gnu.org
` (5 preceding siblings ...)
2014-08-16 17:38 ` vries at gcc dot gnu.org
@ 2014-08-18 8:51 ` vries at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: vries at gcc dot gnu.org @ 2014-08-18 8:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62004
vries at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |alias
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
Summary|dead type-unsafe load |[if-conversion] dead
|replaces type-safe load |type-unsafe load replaces
| |type-safe load
--- Comment #8 from vries at gcc dot gnu.org ---
if-conversion patch and test-case committed to trunk, 4.8 and 4.9.
tail-merge part filed as PR62167 - [tail-merge] dead type-unsafe load replaces
type-safe load
marking resolved, fixed
^ permalink raw reply [flat|nested] 8+ messages in thread
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