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* [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu
@ 2014-07-08 3:49 su at cs dot ucdavis.edu
2014-07-08 5:18 ` [Bug lto/61741] " andi-gcc at firstfloor dot org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: su at cs dot ucdavis.edu @ 2014-07-08 3:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Bug ID: 61741
Summary: wrong code by LTO on x86_64-linux-gnu
Product: gcc
Version: 4.10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: su at cs dot ucdavis.edu
The current gcc trunk miscompiles the following code when using LTO on
x86_64-linux-gnu in both 32-bit and 64-bit modes.
This also seems to affect 4.6.x -- 4.9.x:
(1) the generated code hangs for 4.6.x -- 4.8.x; and
(2) the generated code produces wrong result for 4.9.x.
$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.10.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.10.0 20140707 (experimental) [trunk revision 212319] (GCC)
$
$ gcc-trunk -O0 -c foo.c
$ gcc-trunk -O0 -c main.c
$ gcc-trunk -Os main.o foo.o
$ a.out
0
$
$ gcc-trunk -flto -O0 -c foo.c
$ gcc-trunk -flto -O0 -c main.c
$ gcc-trunk -flto -Os main.o foo.o
$ a.out
1
$
$ cat foo.c
extern int a, b;
void
foo (void)
{
char c = 0;
for (; a; a--)
for (; c >= 0; c++);
if (!c)
b = 1;
}
$ cat main.c
int printf (const char *, ...);
extern void foo (void);
int a = 1, b;
int
main ()
{
foo ();
printf ("%d\n", b);
return 0;
}
$
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug lto/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
@ 2014-07-08 5:18 ` andi-gcc at firstfloor dot org
2014-07-08 5:36 ` su at cs dot ucdavis.edu
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: andi-gcc at firstfloor dot org @ 2014-07-08 5:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Andi Kleen <andi-gcc at firstfloor dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |andi-gcc at firstfloor dot org
--- Comment #1 from Andi Kleen <andi-gcc at firstfloor dot org> ---
char c = 0;
for (; a; a--)
for (; c >= 0; c++);
Don't you rely on signed overflow which is undefined?
-fsanitize=signed-integer-overflow
-fwrapv
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug lto/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
2014-07-08 5:18 ` [Bug lto/61741] " andi-gcc at firstfloor dot org
@ 2014-07-08 5:36 ` su at cs dot ucdavis.edu
2014-07-08 9:19 ` rguenth at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: su at cs dot ucdavis.edu @ 2014-07-08 5:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
--- Comment #2 from Zhendong Su <su at cs dot ucdavis.edu> ---
(In reply to Andi Kleen from comment #1)
> char c = 0;
> for (; a; a--)
> for (; c >= 0; c++);
>
> Don't you rely on signed overflow which is undefined?
No, there is no signed overflow since the variable c is a char so the
increments are performed on int first and then cast back to char: (char) ((int)
c + 1).
The same also holds for short.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug lto/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
2014-07-08 5:18 ` [Bug lto/61741] " andi-gcc at firstfloor dot org
2014-07-08 5:36 ` su at cs dot ucdavis.edu
@ 2014-07-08 9:19 ` rguenth at gcc dot gnu.org
2014-07-09 12:06 ` rguenth at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-08 9:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2014-07-08
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
I believe I fixed sth similar for 4.10 already (it's mismatching
-fstrict-overflow
on compile-time vs. link-time).
I will have a look again.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug lto/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (2 preceding siblings ...)
2014-07-08 9:19 ` rguenth at gcc dot gnu.org
@ 2014-07-09 12:06 ` rguenth at gcc dot gnu.org
2014-07-09 17:15 ` [Bug c/61741] " rguenth at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-09 12:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
The testcase fails without LTO as well if you use -Os -fno-strict-overflow,
fixed by -fno-tree-vrp (not necessarily caused by it though). Also
fails with -O2 -fno-strict-overflow.
Smells similar to PR61184. The patch originally posted for that bug is
thus still required.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (4 preceding siblings ...)
2014-07-09 17:15 ` [Bug c/61741] " rguenth at gcc dot gnu.org
@ 2014-07-09 17:15 ` rguenth at gcc dot gnu.org
2014-07-10 12:21 ` [Bug c/61741] wrong code with -fno-strict-overflow rguenth at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-09 17:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|lto |c
Known to work| |4.10.0
Known to fail| |4.8.3, 4.9.1
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Wed Jul 9 17:14:11 2014
New Revision: 212400
URL: https://gcc.gnu.org/viewcvs?rev=212400&root=gcc&view=rev
Log:
2014-07-09 Richard Biener <rguenther@suse.de>
PR c-family/61741
* c-gimplify.c (c_gimplify_expr): Gimplify self-modify expressions
using unsigned arithmetic if overflow does not wrap instead of
if overflow is undefined.
* c-c++-common/torture/pr61741.c: New testcase.
Added:
trunk/gcc/testsuite/c-c++-common/torture/pr61741.c
Modified:
trunk/gcc/c-family/ChangeLog
trunk/gcc/c-family/c-gimplify.c
trunk/gcc/testsuite/ChangeLog
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk (sofar).
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/61741] wrong code by LTO on x86_64-linux-gnu
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (3 preceding siblings ...)
2014-07-09 12:06 ` rguenth at gcc dot gnu.org
@ 2014-07-09 17:15 ` rguenth at gcc dot gnu.org
2014-07-09 17:15 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-09 17:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|lto |c
Known to work| |4.10.0
Known to fail| |4.8.3, 4.9.1
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Wed Jul 9 17:14:11 2014
New Revision: 212400
URL: https://gcc.gnu.org/viewcvs?rev=212400&root=gcc&view=rev
Log:
2014-07-09 Richard Biener <rguenther@suse.de>
PR c-family/61741
* c-gimplify.c (c_gimplify_expr): Gimplify self-modify expressions
using unsigned arithmetic if overflow does not wrap instead of
if overflow is undefined.
* c-c++-common/torture/pr61741.c: New testcase.
Added:
trunk/gcc/testsuite/c-c++-common/torture/pr61741.c
Modified:
trunk/gcc/c-family/ChangeLog
trunk/gcc/c-family/c-gimplify.c
trunk/gcc/testsuite/ChangeLog
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk (sofar).
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/61741] wrong code with -fno-strict-overflow
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (5 preceding siblings ...)
2014-07-09 17:15 ` rguenth at gcc dot gnu.org
@ 2014-07-10 12:21 ` rguenth at gcc dot gnu.org
2014-07-17 7:58 ` rguenth at gcc dot gnu.org
2014-07-17 7:58 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-10 12:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Jul 10 12:20:32 2014
New Revision: 212430
URL: https://gcc.gnu.org/viewcvs?rev=212430&root=gcc&view=rev
Log:
2014-07-10 Richard Biener <rguenther@suse.de>
PR c-family/61741
* c-c++-common/torture/pr61741.c: Use signed char.
Modified:
trunk/gcc/testsuite/ChangeLog
trunk/gcc/testsuite/c-c++-common/torture/pr61741.c
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/61741] wrong code with -fno-strict-overflow
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (7 preceding siblings ...)
2014-07-17 7:58 ` rguenth at gcc dot gnu.org
@ 2014-07-17 7:58 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-17 7:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Known to work| |4.9.2
Resolution|--- |FIXED
Target Milestone|--- |4.9.2
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk and 4.9 branch.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/61741] wrong code with -fno-strict-overflow
2014-07-08 3:49 [Bug lto/61741] New: wrong code by LTO on x86_64-linux-gnu su at cs dot ucdavis.edu
` (6 preceding siblings ...)
2014-07-10 12:21 ` [Bug c/61741] wrong code with -fno-strict-overflow rguenth at gcc dot gnu.org
@ 2014-07-17 7:58 ` rguenth at gcc dot gnu.org
2014-07-17 7:58 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2014-07-17 7:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61741
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Jul 17 07:57:30 2014
New Revision: 212742
URL: https://gcc.gnu.org/viewcvs?rev=212742&root=gcc&view=rev
Log:
2014-07-17 Richard Biener <rguenther@suse.de>
Backport from mainline
2014-07-10 Richard Biener <rguenther@suse.de>
PR c-family/61741
* c-c++-common/torture/pr61741.c: Use signed char.
2014-07-09 Richard Biener <rguenther@suse.de>
PR c-family/61741
* c-gimplify.c (c_gimplify_expr): Gimplify self-modify expressions
using unsigned arithmetic if overflow does not wrap instead of
if overflow is undefined.
* c-c++-common/torture/pr61741.c: New testcase.
Added:
branches/gcc-4_9-branch/gcc/testsuite/c-c++-common/pr61741.c
Modified:
branches/gcc-4_9-branch/gcc/c-family/ChangeLog
branches/gcc-4_9-branch/gcc/c-family/c-gimplify.c
branches/gcc-4_9-branch/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 10+ messages in thread
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2014-07-08 5:36 ` su at cs dot ucdavis.edu
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