On Tue, May 10, 2011 at 7:14 AM, H.J. Lu <hjl.to...@gmail.com> wrote:
> On Tue, May 10, 2011 at 2:52 AM, Jakub Jelinek <ja...@redhat.com> wrote:
>> On Mon, May 09, 2011 at 01:35:39PM -0700, H.J. Lu wrote:
>>> (gdb) call debug_rtx (rtl)
>>> (var_location d (mem/s/j:SI (plus:DI (subreg:DI (ashift:SI
>>> (entry_value:SI (reg:SI 5 di [ i ]))
>>> (const_int 2 [0x2])) 0)
>>> (symbol_ref:DI ("a") <var_decl 0x7ffff0606000 a>)) [0 a S4 A32]))
>>> (gdb)
>>
>> Ugh, paradoxical subreg? Doesn't that say that the upper 32-bits are
>> undefined? Surely that ought to be zero_extend, sign_extend or something
>> similarly well defined...
>>
>
> With
>
> [hjl@gnu-6 pr48853]$ cat x.i
> extern void abort (void);
> int a[1024];
> volatile short int v;
>
> int
> foo (int i, int j)
> {
> int d = a[i];
> ++v;
> return ++j;
> }
>
> rtl expansion has
>
> ;; Start of basic block ( 2) -> 3
> ;; Pred edge 2 [100.0%] (fallthru)
> (note 6 4 7 3 [bb 3] NOTE_INSN_BASIC_BLOCK)
>
> (debug_insn 7 6 8 3 (var_location:SI D#1 (mem/s/j:SI (plus:DI (subreg:DI
> (ashift
> :SI (entry_value:SI (reg:SI 5 di [ i ]))
> (const_int 2 [0x2])) 0)
> (symbol_ref:DI ("a") <var_decl 0x7ffff0a83000 a>)) [0 a S4 A32]))
> x
> .i:8 -1
> (nil))
>
>
> Where should I look?
>
It comes from expand_debug_expr:
if (offset)
{
enum machine_mode addrmode, offmode;
if (!MEM_P (op0))
return NULL;
op0 = XEXP (op0, 0);
addrmode = GET_MODE (op0);
if (addrmode == VOIDmode)
addrmode = Pmode;
op1 = expand_debug_expr (offset);
if (!op1)
return NULL;
offmode = GET_MODE (op1);
if (offmode == VOIDmode)
offmode = TYPE_MODE (TREE_TYPE (offset));
if (addrmode != offmode)
op1 = simplify_gen_subreg (addrmode, op1, offmode,
subreg_lowpart_offset (addrmode,
offmode));
/* Don't use offset_address here, we don't need a
recognizable address, and we don't want to generate
code. */
op0 = gen_rtx_MEM (mode, simplify_gen_binary (PLUS, addrmode,
op0, op1));
}
(gdb) call debug_rtx (op1)
(ashift:SI (entry_value:SI (reg:SI 5 di [ i ]))
(const_int 2 [0x2]))
(gdb) call debug_rtx (op0)
(symbol_ref:DI ("a") <var_decl 0x7ffff0a83000 a>)
(gdb) p offmode
$9 = SImode
(gdb) p addrmode
$10 = DImode
(gdb)
--
H.J.
