Re: Mark variables addressable if they are copied using libcall in RTL expander

[Easwaran Raman <eraman@google.com>]

On Wed, Jun 22, 2011 at 7:13 AM, Eric Botcazou <ebotcazou@adacore.com> 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.  */