On Thu, Jun 21, 2018 at 2:22 PM, Marek Polacek <pola...@redhat.com> wrote:
> The following testcase is rejected because, for this line:
>
> bool b = X() ?: false;
>
> arg2 is missing and arg1 is a TARGET_EXPR. A TARGET_EXPR is a class
> prvalue so we wrap it in a SAVE_EXPR. Later when building 'this' we
> call build_this (SAVE_EXPR <TARGET_EXPR <...>>) which triggers lvalue_error:
> 5856 cp_lvalue_kind kind = lvalue_kind (arg);
> 5857 if (kind == clk_none)
> 5858 {
> 5859 if (complain & tf_error)
> 5860 lvalue_error (input_location, lv_addressof);
> because all SAVE_EXPRs are non-lvalue.
>
> Since
> a) cp_build_addr_expr_1 can process xvalues and class prvalues,
> b) TARGET_EXPRs are only evaluated once (gimplify_target_expr),
> I thought we could do the following. The testcase ensures that
> with the omitted operand we only construct X once.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-06-21 Marek Polacek <pola...@redhat.com>
>
> PR c++/86184
> * call.c (build_conditional_expr_1): Don't wrap TARGET_EXPRs
> in a SAVE_EXPR.
>
> * g++.dg/ext/cond3.C: New test.
>
> --- gcc/cp/call.c
> +++ gcc/cp/call.c
> @@ -4806,6 +4806,10 @@ build_conditional_expr_1 (location_t loc, tree arg1,
> tree arg2, tree arg3,
> /* Make sure that lvalues remain lvalues. See g++.oliva/ext1.C. */
> if (lvalue_p (arg1))
> arg2 = arg1 = cp_stabilize_reference (arg1);
> + else if (TREE_CODE (arg1) == TARGET_EXPR)
> + /* TARGET_EXPRs are only expanded once, don't wrap it in a SAVE_EXPR,
> + rendering it clk_none of clk_class. */
> + arg2 = arg1;
> else
> arg2 = arg1 = cp_save_expr (arg1);
How about adding the special handling in cp_save_expr rather than
here, so other callers also benefit?
OK with that change.
Jason
