[Bug other/43949] New: bogus warning: array subscript is above array bounds

[joachim dot reichel at gmx dot de]

$ cat test.cpp
void f();

int c[3];
int result;

struct Vector {
    static int get(int i) {
        if (i >= 3)
            f();
        return c[i];
    }
};

void g()
{
    for (int i = 0; i < 3; ++i) {
        const int index = i % 3;
        result = Vector::get(index) + Vector::get(index);
    }
}

$ g++ -Wall -c test.cpp
[no warnings]

$ g++ -Wall -c -O2 test.cpp
test.cpp: In function ‘void g()’:
test.cpp:10: error: array subscript is above array bounds

$ g++ -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.2-9'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.3 20100108 (prerelease) (Debian 4.4.2-9)

The bogus warning disappears if
- (index) is replaced by (i)
- Vector::get(index) is assigned to result (no addition)
- the if statement is removed (call of f() in all cases)
- get() is a global function

The bogus warning does not appear in gcc 4.2.4 (Debian 4.2.4-6). It appears
also in 4.3.2 (Debian 4.3.2-1.1) and gcc 4.5.0 (GCC).


-- 
           Summary: bogus warning: array subscript is above array bounds
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: joachim dot reichel at gmx dot de
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949