[Bug c/27214] New: The C frontend introduces undefined pointer overflow

[rguenth at gcc dot gnu dot org]

The C frontend creates pointer arithmetic that assumes that pointer
overflow is defined (and wraps).

char *foo(char *p)
{
  return p + -4;
}

results in

foo (p)
{
  char * D.1523;

  D.1523 = p + -4B;
  return D.1523;
}

this is via c-common.c:pointer_int_sum().

 <plus_expr 0xb7da4144
    type <pointer_type 0xb7db405c
        type <integer_type 0xb7dac170 char public string-flag QI
            size <integer_cst 0xb7d9d1f8 constant invariant 8>
            unit size <integer_cst 0xb7d9d210 constant invariant 1>
            align 8 symtab 0 alias set -1 precision 8 min <integer_cst
0xb7d9d258 -128> max <integer_cst 0xb7d9d2b8 127>
            pointer_to_this <pointer_type 0xb7db405c>>
        unsigned SI
        size <integer_cst 0xb7d9d3f0 constant invariant 32>
        unit size <integer_cst 0xb7d9d180 constant invariant 4>
        align 32 symtab 0 alias set -1>

    arg 0 <parm_decl 0xb7da5140 p type <pointer_type 0xb7db405c>
        used unsigned SI file t.c line 1 size <integer_cst 0xb7d9d3f0 32> unit
size <integer_cst 0xb7d9d180 4>
        align 32 context <function_decl 0xb7e2d980 foo> initial <pointer_type
0xb7db405c> arg-type <pointer_type 0xb7db405c>>
    arg 1 <integer_cst 0xb7e35eb8 type <pointer_type 0xb7db405c> constant
invariant 4294967292>>


-- 
           Summary: The C frontend introduces undefined pointer overflow
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 27039
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27214