[Bug c++/39551] New: C++ frontend not warn about unused dereference operator with -Wunused-value
Given the following code, where the value of the dereference operation is
unused,
$ cat unused_deref.c
void Foo(int* x) {
*x++;
}
if it is compiled with gcc (C frontend) with -Wunused-value option, we get a
warning.
$ gcc -Wunused-value -c unused_deref.c
unused_deref.c: In function 'Foo':
unused_deref.c:2: warning: value computed is not used
However, if the code is compiled with g++, we don't get the warning.
$ g++ -Wunused-value -c unused_deref.c
After doing some triage, it appears that C++ frontend silently gets rid of
INDIRECT_REF operator (without emitting any warnings) when it processes the
expression '*x++' in convert_to_void() in cp/cvt.c.
Here is the version string of the compiler that I tried:
gcc version 4.4.0 20090324 (experimental) (GCC)
--
Summary: C++ frontend not warn about unused dereference operator
with -Wunused-value
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lcwu at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39551
[Bug c++/39551] C++ frontend not warn about unused dereference operator with -Wunused-value
--- Comment #1 from lcwu at gcc dot gnu dot org 2009-04-15 17:56 --- Subject: Bug 39551 Author: lcwu Date: Wed Apr 15 17:55:50 2009 New Revision: 146132 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=146132 Log: PR c++/39551 * gcc/cp/call.c (build_over_call): Set TREE_NO_WARNING on the compiler-generated INDIRECT_REF expression. * gcc/cp/cvt.c (convert_to_void): Emit warning when stripping off INDIRECT_REF. * gcc/testsuite/g++.dg/warn/Wunused-13.C: New testcase. Added: trunk/gcc/testsuite/g++.dg/warn/Wunused-13.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/call.c trunk/gcc/cp/cvt.c trunk/gcc/testsuite/ChangeLog -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39551
[Bug c++/39551] C++ frontend not warn about unused dereference operator with -Wunused-value
--- Comment #2 from lcwu at gcc dot gnu dot org 2009-04-15 18:03 --- The fix for this bug was committed at revision 146132. -- lcwu at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||FIXED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39551
[Bug c++/39803] New: Bogus 'unused value' warning on declarations of non-POD arrays
When compiling the following program using the mainline GCC (4.5) with -Wunused
flag, we get a bogus "unused value" warning on the array declaration:
$ cat Wunused-14.C
#include
using std::pair;
int foo() {
pair components[3];
components[0].first = 0;
return 0;
}
$ g++ -Wunused -c Wunused-14.C
Wunused-14.C: In function 'int foo()':
Wunused-14.C:6: warning: value computed is not used
Here is the version string of the compiler used:
Target: x86_64-unknown-linux-gnu
gcc version 4.5.0 20090414 (experimental) (GCC)
--
Summary: Bogus 'unused value' warning on declarations of non-POD
arrays
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lcwu at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39803
[Bug c++/39803] Bogus 'unused value' warning on declarations of non-POD arrays
--- Comment #1 from lcwu at gcc dot gnu dot org 2009-04-17 23:07 ---
This bogus warning started to show up after the fix for PR c++/39551 was
submitted (at revision 146132). And the root cause for the issue is that C++
front-end generates the following code to initialize the local 'pair' array:
(see build_vec_init() in cp/init.c)
*(struct pair[3] *) ({
(D.2247 = (struct pair *) &components);
(D.2248 = D.2247);
(D.2249 = 2);
for_stmt
{
D.2249 != -1;
--D.2249;
__comp_ctor (NON_LVALUE_EXPR );
++D.2248;
}
D.2247; })
The INDIRECT_REF operation (*) in the above code was later determined useless
and therefore deleted. However, since we didn't know that the INDIRECT_REF
expression was actually created by the compiler (instead of coming from the
user code) and therefore mistakenly emit an 'unused value' warning.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39803
[Bug c++/39803] Bogus 'unused value' warning on declarations of non-POD arrays
--- Comment #2 from lcwu at gcc dot gnu dot org 2009-04-20 21:13 --- Subject: Bug 39803 Author: lcwu Date: Mon Apr 20 21:13:08 2009 New Revision: 146454 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=146454 Log: PR c++/39803 * gcc/cp/init.c (build_vec_init): Set TREE_NO_WARNING on the compiler-generated INDIRECT_REF expression. * gcc/testsuite/g++.dg/warn/Wunused-14.C: New test. Added: trunk/gcc/testsuite/g++.dg/warn/Wunused-14.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/init.c trunk/gcc/testsuite/ChangeLog -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39803
[Bug c++/39803] Bogus 'unused value' warning on declarations of non-POD arrays
--- Comment #3 from lcwu at gcc dot gnu dot org 2009-04-20 21:45 --- The fix for this bug was committed to mainline at revision 146454. -- lcwu at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||FIXED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39803
[Bug bootstrap/39968] [4.5 Regression] ./plugin-version.h:11: error: 'gcc_version' defined but not used
--- Comment #2 from lcwu at gcc dot gnu dot org 2009-04-30 00:34 --- The sole use of gcc_version in plugin.c is in function try_init_one_plugin, which is guarded by the macro ENABLE_PLUGIN. Since ENABLE_PLUGIN is set to 0 on the Darwin systems, the function was compiled out. I think we need to guard the inclusion of plugin-version.h with ENABLE_PLUGIN as well. -- lcwu at gcc dot gnu dot org changed: What|Removed |Added CC||dnovillo at google dot com, ||lcwu at gcc dot gnu dot org, ||espindola at google dot com Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Last reconfirmed|-00-00 00:00:00 |2009-04-30 00:34:30 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39968
[Bug c++/44128] New: C++ frontend not warn on type shadowing with -Wshadow
This bug is a follow-up to bug c++/44122.
Given the following program:
$ cat t.c
typedef long Py_ssize_t;
void bar() {
typedef int Py_ssize_t;
Py_ssize_t pos;
}
When compiled with the C compiler with -Wshadow flag, a shadow warning is
emitted.
$ gcc -c t.c -Wshadow
t.c: In function bar:
t.c:5:14: warning: declaration of Py_ssize_t shadows a global declaration
[-Wshadow]
t.c:1:14: warning: shadowed declaration is here [-Wshadow]
However, when using the C++ compiler with the same flag, no warning is emitted.
$ g++ -c t.c -Wshadow
I think C++ frontend should warn on this case as the C frontend.
--
Summary: C++ frontend not warn on type shadowing with -Wshadow
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lcwu at gcc dot gnu dot org
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44128
