store_expr, expr_size, and C++

[Steve Ellcey]

I am looking at PR target/30826 (an IA64 ABI bug) and have come up with
a patch that basically involves turning off the
CALL_EXPR_RETURN_SLOT_OPT optimization in some instances and forcing GCC
to create a temporary for the (large aggragete) return value of a
function and then copying that temporary value to the desired target.

The problem I am running into is with C++ code in store_expr.  I get to
this if statement:

  if ((! rtx_equal_p (temp, target)
       || (temp != target && (side_effects_p (temp)
                              || side_effects_p (target))))
      && TREE_CODE (exp) != ERROR_MARK
      /* If store_expr stores a DECL whose DECL_RTL(exp) == TARGET,
         but TARGET is not valid memory reference, TEMP will differ
         from TARGET although it is really the same location.  */
      && !(alt_rtl && rtx_equal_p (alt_rtl, target))
      /* If there's nothing to copy, don't bother.  Don't call
         expr_size unless necessary, because some front-ends (C++)
         expr_size-hook must not be given objects that are not
         supposed to be bit-copied or bit-initialized.  */
      && expr_size (exp) != const0_rtx)

and I hit a gcc_assert when calling expr_size().  Even if I avoided this
somehow I would hit it later when calling:

        emit_block_move (target, temp, expr_size (exp),
                         (call_param_p
                          ? BLOCK_OP_CALL_PARM : BLOCK_OP_NORMAL));

So my question is:  is there a way to handle this copy/assignment in C++
without depending on expr_size.  I noticed PR middle-end/30017 (turning
memcpys into assignments) which seems to have some of the same issues of
getting expr_size for C++ expressions but that defect is still open so
it doesn't look like there is an answer yet.

Anyone have some ideas on this problem?

Steve Ellcey
sje@cup.hp.com