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* [Bug c++/35835] New: Compiler fails to recognize match of local "extern" declarations
@ 2008-04-05 18:33 oder at eleks dot lviv dot ua
2008-04-05 19:56 ` [Bug c++/35835] " pinskia at gcc dot gnu dot org
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: oder at eleks dot lviv dot ua @ 2008-04-05 18:33 UTC (permalink / raw)
To: gcc-bugs
Consider following program
======= begin of test.cpp ========
#include <stdio.h>
static inline void SetValue(int i)
{
extern int g_iValue;
g_iValue = i;
}
static inline int GetValue()
{
extern int g_iValue;
return g_iValue;
}
int g_iValue = 0;
int main()
{
int iValueSave = GetValue();
SetValue(1);
printf("%d\n", GetValue());
SetValue(iValueSave);
return 0;
}
======= end of test.cpp ========
I use this apptoach to only publish get/set global variable accessors in header
while keeping variable itself hidden in cpp.
If compiled with optimizations turned on, compiler fails identify two local
"extern" declarations as a single memory object and uses initial value
retrieved for iValueSafe in call to printf as well (as if SetValue() was
unrelated to g_iValue).
If compiled and run, program outputs 0 instead of 1.
osx-leopard:build oder$ g++ -O3 -o test test.cpp
osx-leopard:build oder$ ./test
0
Output of "g++ -v" is:
Using built-in specs.
Target: powerpc-apple-darwin9
Configured with: /var/tmp/gcc/gcc-5478~1/src/configure --disable-checking
-enable-werror --prefix=/usr --mandir=/share/man
--enable-languages=c,objc,c++,obj-c++
--program-transform-name=/^[cg][^.-]*$/s/$/-4.0/
--with-gxx-include-dir=/include/c++/4.0.0 --with-slibdir=/usr/lib
--build=powerpc-apple-darwin9 --host=powerpc-apple-darwin9
--target=powerpc-apple-darwin9
Thread model: posix
gcc version 4.0.1 (Apple Inc. build 5478)
--
Summary: Compiler fails to recognize match of local "extern"
declarations
Product: gcc
Version: 4.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: oder at eleks dot lviv dot ua
GCC build triplet: ppc
GCC host triplet: ppc
GCC target triplet: ppc
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35835
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/35835] Compiler fails to recognize match of local "extern" declarations
2008-04-05 18:33 [Bug c++/35835] New: " oder at eleks dot lviv dot ua
@ 2008-04-05 19:56 ` pinskia at gcc dot gnu dot org
2008-04-05 20:02 ` oder at eleks dot lviv dot ua
2008-04-05 21:16 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2008-04-05 19:56 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gcc dot gnu dot org 2008-04-05 19:56 -------
First, this bug should be filed with Apple as you are using Apple's modified
compiler. Second 4.0.x is no longer being maintained, so please try 4.1.x.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35835
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/35835] Compiler fails to recognize match of local "extern" declarations
2008-04-05 18:33 [Bug c++/35835] New: " oder at eleks dot lviv dot ua
2008-04-05 19:56 ` [Bug c++/35835] " pinskia at gcc dot gnu dot org
@ 2008-04-05 20:02 ` oder at eleks dot lviv dot ua
2008-04-05 21:16 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 5+ messages in thread
From: oder at eleks dot lviv dot ua @ 2008-04-05 20:02 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from oder at eleks dot lviv dot ua 2008-04-05 20:02 -------
(In reply to comment #1)
> First, this bug should be filed with Apple as you are using Apple's modified
> compiler. Second 4.0.x is no longer being maintained, so please try 4.1.x.
I don't have root access to the build machine and I can only use the version of
compiler which is installed there.
Also, I don't think the problem is related to target platform. It should be
reproduceable on all the platforms.
If you can't try it yourself, I can run the test on SunOS or Linux tomorrow.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35835
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/35835] Compiler fails to recognize match of local "extern" declarations
2008-04-05 18:33 [Bug c++/35835] New: " oder at eleks dot lviv dot ua
2008-04-05 19:56 ` [Bug c++/35835] " pinskia at gcc dot gnu dot org
2008-04-05 20:02 ` oder at eleks dot lviv dot ua
@ 2008-04-05 21:16 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2008-04-05 21:16 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from pinskia at gcc dot gnu dot org 2008-04-05 21:16 -------
(In reply to comment #4)
> (works with the C frontend)
> We don't share the decls of g_iValue properly, but doesn't this program
> violate the ODR anyway?
No it does not as there is only one g_iValue variable. The reasoning behind
using extern int g_iValue; is so it does not get into the global scope.
The reason why the C front-end works is because we have a non TU scope which we
add decls to and then look up global decls that way and get that decl instead
of creating a new one.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |wrong-code
Last reconfirmed|0000-00-00 00:00:00 |2008-04-05 21:16:01
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35835
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-12-20 8:11 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2021-12-17 11:48 ` [Bug c++/35835] Compiler fails to recognize match of local "extern" declarations pinskia at gcc dot gnu.org
2021-12-20 8:11 ` egallager at gcc dot gnu.org
2008-04-05 18:33 [Bug c++/35835] New: " oder at eleks dot lviv dot ua
2008-04-05 19:56 ` [Bug c++/35835] " pinskia at gcc dot gnu dot org
2008-04-05 20:02 ` oder at eleks dot lviv dot ua
2008-04-05 21:16 ` pinskia at gcc dot gnu dot org
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