[Bug c/28940] [4.0/4.1/4.2 Regression] address selection does not work correctly

["rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #7 from rguenth at gcc dot gnu dot org  2006-10-11 12:23 -------
We're not folding

  return (int) *((char *) (long unsigned int) i + &a + 1B) + (int) *((char *)
(long unsigned int) i + &b + 1B);

one reason is that the C frontend decomposes &a[i], one is the array-to-pointer
decay code of the frontend.  Compare that to the C++ frontend where we manage
to fold to

return <retval> = (int) a[(<unnamed type>) (long unsigned int) i + 1] + (int)
b[(<unnamed type>) (long unsigned int) i + 1];

and so do the optimization.

In particular, fold-const.c:try_move_mult_to_index does not recognize
 <addr_expr 0x2b0bb95fd0c0
    type <pointer_type 0x2b0bb9615420
        type <integer_type 0x2b0bb96022c0 char public string-flag QI
            size <integer_cst 0x2b0bb95f27e0 constant invariant 8>
            unit size <integer_cst 0x2b0bb95f2810 constant invariant 1>
            align 8 symtab 0 alias set -1 precision 8 min <integer_cst
0x2b0bb95f28a0 -128> max <integer_cst 0x2b0bb95f2960 127>
            pointer_to_this <pointer_type 0x2b0bb9615420>>
        public unsigned DI
        size <integer_cst 0x2b0bb95f2d80 constant invariant 64>
        unit size <integer_cst 0x2b0bb95f2db0 constant invariant 8>
        align 64 symtab 0 alias set -1>
    constant invariant
    arg 0 <var_decl 0x2b0bb97bcbb0 a
        type <array_type 0x2b0bb97bcb00 type <integer_type 0x2b0bb96022c0 char>
            BLK
            size <integer_cst 0x2b0bb97ce3f0 constant invariant 80>
            unit size <integer_cst 0x2b0bb97ce390 constant invariant 10>
            align 8 symtab 0 alias set -1 domain <integer_type 0x2b0bb97bca50>>
        addressable used public static common BLK defer-output file t.i line 1
size <integer_cst 0x2b0bb97ce3f0 80> unit size <integer_cst 0x2b0bb97ce390 10>
        align 8>>
as &a[0].


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|rtl-optimization            |c


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28940