[Bug tree-optimization/45180] New: bogus warning: array subscript is above array bounds

[joachim dot reichel at gmx dot de]

Please see 43949 which was about a very similar test case.

$ 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(int index)
{
    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:10:19: error: array subscript is above array bounds

$ g++ -v
Using built-in specs.
COLLECT_GCC=/prefix/gcc-4.5.0/x86_64-unknown-linux-gnu/bin/g++
COLLECT_LTO_WRAPPER=/prefix/gcc-4.5.0/x86_64-unknown-linux-gnu/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.5.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/prefix/gcc-4.5.0
--exec-prefix=/prefix/gcc-4.5.0/x86_64-unknown-linux-gnu
--enable-version-specific-runtime-libs --enable-stage1-checking --disable-nls
--with-system-zlib --enable-multilib --enable-languages=c,c++,objc
--with-gmp-include=/prefix/gmp-4.2.2/x86_64-unknown-linux-gnu/include
--with-gmp-lib=/prefix/gmp-4.2.2/x86_64-unknown-linux-gnu/lib
--with-mpfr-include=/prefix/mpfr-2.4.2/include
--with-mpfr-lib=/prefix/mpfr-2.4.2/x86_64-unknown-linux-gnu/lib
--with-mpc-include=/prefix/mpc-0.8.1/include
--with-mpc-lib=/prefix/mpc-0.8.1/x86_64-unknown-linux-gnu/lib --with-gnu-as
--with-as=/prefix/binutils-2.20.1/x86_64-unknown-linux-gnu/bin/as --with-gnu-ld
--with-ld=/prefix/binutils-2.20.1/x86_64-unknown-linux-gnu/bin/ld
Thread model: posix
gcc version 4.5.0 (GCC)

The bogus warning disappears if
- Vector::get(index) is assigned to result (no addition)
- 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), 4.4.4 (Debian 4.4.4-7) and 4.5.0 (GCC).

Note that in contrast to PR43949 in this case the array subscript *could* be
above array bounds depending on how g() is called, but in the code snippet
itself there is no such call.


-- 
           Summary: bogus warning: array subscript is above array bounds
           Product: gcc
           Version: 4.5.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        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=45180