On Wed, Jun 22, 2011 at 7:13 AM, Eric Botcazou <[email protected]> wrote:
>> I fear this isn't enough considering pass-by-value aggregates that
>> are callee copied.
>
> It's indeed not sufficient for arguments passed by reference but
> callee-copied.
>
> This is PR target/49454. For gcc.c-torture/execute/20000717-1.c:
>
> typedef struct trio { int a, b, c; } trio;
>
> int
> foo (trio t, int i)
> {
> return bar (i, t);
> }
>
> yiedls in the .optimized dump:
>
> foo (struct trio t, int i)
> {
> int D.1968;
> struct trio t.0;
>
> <bb 2>:
> t.0 = t;
> D.1968_2 = bar (i_1(D), t.0);
> return D.1968_2;
> }
>
> and the aggregate copy is elided by DSE because t.0 isn't may_be_aliased.
> This
> seems to be a pre-existing bug though: its address is passed to bar in RTL.
>
> --
> Eric Botcazou
>
Is the following patch a reasonable fix for this case? I assume I
should add similar code inside emit_library_call_value_1.
-Easwaran
--- gcc/calls.c (revision 175081)
+++ gcc/calls.c (working copy)
@@ -1073,6 +1073,8 @@ initialize_argument_information (int num_actuals A
callee_copies
= reference_callee_copied (args_so_far, TYPE_MODE (type),
type, argpos < n_named_args);
+ if (callee_copies)
+ mark_addressable (args[i].tree_value);
/* If we're compiling a thunk, pass through invisible references
instead of making a copy. */
