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* [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect
@ 2011-02-11 15:40 us15 at os dot inf.tu-dresden.de
2011-02-11 15:43 ` [Bug rtl-optimization/47698] " us15 at os dot inf.tu-dresden.de
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: us15 at os dot inf.tu-dresden.de @ 2011-02-11 15:40 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Summary: CMOV accessing volatile memory with read side effect
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: us15@os.inf.tu-dresden.de
In the attached testcase, the variable "mmio" is a memory-mapped device
register with read side effects. It must only be accessed if "cond" is true.
When compiling the testcase:
gcc -Os -c testcase.cc -o testcase.o
the following output is generated:
0000000000000000 <foo()>:
0: 31 c0 xor %eax,%eax
2: 48 83 3d 00 00 00 00 cmpq $0x0,0x0(%rip) # a <foo()+0xa>
9: 00
a: 48 0f 45 05 00 00 00 cmovne 0x0(%rip),%rax # 12 <foo()+0x12>
11: 00
12: c3 retq
Due to the use of CMOV, gcc is reading the memory location regardless of "cond"
being true, even though "mmio" is casted to volatile.
Reading "mmio" through a volatile pointer, as in
return *static_cast<volatile unsigned long *>(&mmio);
does not get rid of the CMOV either.
What is the correct way to ensure mmio is read if and only if cond is true?
My gcc version is: gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-slackware-linux/4.6.0/lto-wrapper
Target: x86_64-slackware-linux
Configured with: ../gcc-svn/configure --prefix=/usr --libdir=/usr/lib64
--mandir=/usr/man --infodir=/usr/info --enable-shared --enable-bootstrap
--enable-languages=c,c++,lto --enable-threads=posix --enable-checking=release
--with-system-zlib --with-python-dir=/lib64/python2.6/site-packages
--disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp
--enable-lto --with-gnu-ld --verbose --disable-multilib
--target=x86_64-slackware-linux --build=x86_64-slackware-linux
--host=x86_64-slackware-linux
Thread model: posix
gcc version 4.6.0 20110211 (experimental) (GCC)
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
@ 2011-02-11 15:43 ` us15 at os dot inf.tu-dresden.de
2011-02-11 16:04 ` us15 at os dot inf.tu-dresden.de
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: us15 at os dot inf.tu-dresden.de @ 2011-02-11 15:43 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
--- Comment #1 from Udo Steinberg <us15 at os dot inf.tu-dresden.de> 2011-02-11 15:40:27 UTC ---
Created attachment 23308
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23308
Testcase
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
2011-02-11 15:43 ` [Bug rtl-optimization/47698] " us15 at os dot inf.tu-dresden.de
@ 2011-02-11 16:04 ` us15 at os dot inf.tu-dresden.de
2011-02-11 16:36 ` rguenth at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: us15 at os dot inf.tu-dresden.de @ 2011-02-11 16:04 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Udo Steinberg <us15 at os dot inf.tu-dresden.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
Attachment #23308|0 |1
is obsolete| |
--- Comment #2 from Udo Steinberg <us15 at os dot inf.tu-dresden.de> 2011-02-11 15:42:30 UTC ---
Created attachment 23309
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23309
Testcase
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
2011-02-11 15:43 ` [Bug rtl-optimization/47698] " us15 at os dot inf.tu-dresden.de
2011-02-11 16:04 ` us15 at os dot inf.tu-dresden.de
@ 2011-02-11 16:36 ` rguenth at gcc dot gnu.org
2011-02-11 17:07 ` matz at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-02-11 16:36 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011.02.11 16:34:48
Ever Confirmed|0 |1
Known to fail| |4.3.4, 4.5.2, 4.6.0
--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-02-11 16:34:48 UTC ---
Confirmed. C testcase:
extern volatile unsigned long mmio;
unsigned long foo(int cond)
{
if (cond)
return mmio;
return 0;
}
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (2 preceding siblings ...)
2011-02-11 16:36 ` rguenth at gcc dot gnu.org
@ 2011-02-11 17:07 ` matz at gcc dot gnu.org
2011-02-11 17:57 ` hjl.tools at gmail dot com
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: matz at gcc dot gnu.org @ 2011-02-11 17:07 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Michael Matz <matz at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |matz at gcc dot gnu.org
--- Comment #4 from Michael Matz <matz at gcc dot gnu.org> 2011-02-11 17:05:57 UTC ---
noce_operand_ok doesn't disregard volatile MEMs:
/* We special-case memories, so handle any of them with
no address side effects. */
if (MEM_P (op))
return ! side_effects_p (XEXP (op, 0));
But I don't see where we would handle volatile MEMs in any sensible
way. We happily fiddle with such operands resulting in the problem.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (3 preceding siblings ...)
2011-02-11 17:07 ` matz at gcc dot gnu.org
@ 2011-02-11 17:57 ` hjl.tools at gmail dot com
2011-11-07 8:42 ` kyukhin at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: hjl.tools at gmail dot com @ 2011-02-11 17:57 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> 2011-02-11 17:48:43 UTC ---
(In reply to comment #4)
> noce_operand_ok doesn't disregard volatile MEMs:
>
> /* We special-case memories, so handle any of them with
> no address side effects. */
> if (MEM_P (op))
> return ! side_effects_p (XEXP (op, 0));
>
> But I don't see where we would handle volatile MEMs in any sensible
> way. We happily fiddle with such operands resulting in the problem.
cmov pattern should disallow operand with volatile MEM.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (4 preceding siblings ...)
2011-02-11 17:57 ` hjl.tools at gmail dot com
@ 2011-11-07 8:42 ` kyukhin at gcc dot gnu.org
2011-11-08 13:46 ` ebotcazou at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: kyukhin at gcc dot gnu.org @ 2011-11-07 8:42 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
--- Comment #6 from Kirill Yukhin <kyukhin at gcc dot gnu.org> 2011-11-07 08:42:00 UTC ---
Author: kyukhin
Date: Mon Nov 7 08:41:55 2011
New Revision: 181075
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=181075
Log:
gcc/
PR rtl-optimization/47698
* ifconv.c (noce_operand_ok): prevent CMOV generation
for volatile mem.
gcc/testsuite/
PR rtl-optimization/47698
* gcc.target/i386/47698.c: New test.
Added:
trunk/gcc/testsuite/gcc.target/i386/47698.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/ifcvt.c
trunk/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (5 preceding siblings ...)
2011-11-07 8:42 ` kyukhin at gcc dot gnu.org
@ 2011-11-08 13:46 ` ebotcazou at gcc dot gnu.org
2012-01-21 20:27 ` pinskia at gcc dot gnu.org
2021-07-29 22:34 ` pinskia at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: ebotcazou at gcc dot gnu.org @ 2011-11-08 13:46 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-11-08 13:44:22 UTC ---
Author: ebotcazou
Date: Tue Nov 8 13:44:11 2011
New Revision: 181161
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=181161
Log:
PR rtl-optimization/47698
* ifcvt.c (noce_operand_ok): Move around comment.
Modified:
trunk/gcc/ChangeLog
trunk/gcc/ifcvt.c
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (6 preceding siblings ...)
2011-11-08 13:46 ` ebotcazou at gcc dot gnu.org
@ 2012-01-21 20:27 ` pinskia at gcc dot gnu.org
2021-07-29 22:34 ` pinskia at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu.org @ 2012-01-21 20:27 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
Target Milestone|--- |4.7.0
--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-21 20:18:48 UTC ---
Fixed.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/47698] CMOV accessing volatile memory with read side effect
2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
` (7 preceding siblings ...)
2012-01-21 20:27 ` pinskia at gcc dot gnu.org
@ 2021-07-29 22:34 ` pinskia at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-29 22:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47698
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |regehr at cs dot utah.edu
--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 35764 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 10+ messages in thread
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2011-02-11 15:40 [Bug rtl-optimization/47698] New: CMOV accessing volatile memory with read side effect us15 at os dot inf.tu-dresden.de
2011-02-11 15:43 ` [Bug rtl-optimization/47698] " us15 at os dot inf.tu-dresden.de
2011-02-11 16:04 ` us15 at os dot inf.tu-dresden.de
2011-02-11 16:36 ` rguenth at gcc dot gnu.org
2011-02-11 17:07 ` matz at gcc dot gnu.org
2011-02-11 17:57 ` hjl.tools at gmail dot com
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