[ https://issues.apache.org/jira/browse/STDCXX-904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12594460#action_12594460 ] 

Martin Sebor commented on STDCXX-904:
-------------------------------------

Reduced test case I sent to HP:
{noformat}
$ cat u.cpp && aCC -V +O2 +w -c t.cpp
void foo (const char*);

int main () {

    struct B {
        char x [4];

        void bar (unsigned n) {
            for (unsigned i = 3; i != n - 1; --i)
                x [i] = x [i - n];
        }
    } x;

    for (unsigned i = 0; i != 1; ++i) {

        x.bar (i % 4);

        foo (x.x);
    }
}

aCC: HP C/aC++ B3910B A.06.16 [Nov 26 2007]
"t.cpp", line 13, procedure main: warning #20206-D: Out of bound access (In
          expression "memmove(&(&x)->x[2]+1 - (long long)(3 -
          n),&(&x)->x[(int)(2 - n)]+1 - (long long)(3 - n),3 - n)",
          &(&x)->x[2]+1 - (long long)(3 - n) (type: char [4]) (defined by
          (&x)->x) has byte range [0 .. 3], writing byte range [0 .. 4].)
{noformat}

> [HP aCC 6.16] bogus cadvise warning #20206 in optimized code
> ------------------------------------------------------------
>
>                 Key: STDCXX-904
>                 URL: https://issues.apache.org/jira/browse/STDCXX-904
>             Project: C++ Standard Library
>          Issue Type: Bug
>          Components: External
>    Affects Versions: 4.2.1
>         Environment: $ uname -sr && aCC -V 
> HP-UX B.11.31
> aCC: HP C/aC++ B3910B A.06.16 [Nov 26 2007] 
>            Reporter: Travis Vitek
>
> This is a simplified version of 23.bitset.cpp that shows a bogus out of bound access cadvise warning. 
> {noformat}
> void __rw_bitset (unsigned*, unsigned, const char*, unsigned, unsigned, unsigned);
> template <unsigned _Size>
> class bitset
> {
>     unsigned bits_ [1];
> public:
>     bitset (const char *__str, unsigned __pos, unsigned __n) {
>         __rw_bitset (bits_, _Size, __str, 0, __pos, __n);
>     }
> };
> template <unsigned _Size>
> struct test_set
> {
>     char bits_ [_Size + 1]; // includes a null terminator
>     test_set () {
>         for (unsigned i = 0; i != _Size; ++i)
>             bits_ [i] = '0';
>         bits_ [_Size] = '\0';   
>     }
>     test_set& operator>>= (unsigned n) {
>         for (unsigned i = _Size - 1; i != n - 1; --i)
>             bits_ [i] = bits_ [i - n];
>         for (unsigned j = n; j != 0; )
>             bits_ [--j] = '0';
>         return *this;
>     }
> };
> template <unsigned _Size>
> void run_test ()
> {
>     test_set<_Size> ts0;
>     const unsigned M = _Size + 1;
>     for (unsigned i = 0; i != 1; ++i) {
>         const unsigned n = i % M;
>          
>         const test_set<_Size> ts1 = (ts0 >>= n);
>         (void)&ts1;
>         const bitset<_Size> bs0 (ts0.bits_, 0, _Size);
>     }
> }
> int main (int argc, char *argv[])
> {
>     run_test<31>();
>     return 0;
> }
> {noformat}
> The result of compiling this code with -O2 is...
> {noformat}
> aCC -c -mt \
>   -I/amd/devco/vitek/stdcxx/4.2.x/include \
>   -I/amd/devco/vitek/stdcxx/4.2.x/build/include \
>   -I/amd/devco/vitek/stdcxx/4.2.x/tests/include \
>   -AA  +O2  +DD64 +w \
>   +W392,655,684,818,819,849 \
>   +W2193,2236,2261,2340,2401,2487 \
>   +W4227,4229,4231,4235,4237,4249 \
>   +W4255,4272,4284,4285,4286,4296,4297 \
>   +W3348 u.cpp
> "u.cpp", line 29, procedure main: warning #20206-D: Out of bound access \
>   (In expression "memmove(&(&ts0)->bits_[30]+1 - (31 - n),&(&ts0)->bits_[(30 - n)]+1 - (31 - n),31 - n)", &(&ts0)->bits_[30]+1 - (31 - n)  \
> (type: char [32]) (defined by (&ts0)->bits_) has byte range [0 .. 31], writing byte range [0 .. 60].)
> {noformat}
> The code compiles without warning if the optimization level is reduced to -O1.

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