re PR c++/79937 (ICE in replace_placeholders_r)

re PR c++/79937 (ICE in replace_placeholders_r)

	PR c++/79937
	PR c++/82410
	* tree.h (TARGET_EXPR_NO_ELIDE): Define.
	* gimplify.c (gimplify_modify_expr_rhs): Don't elide TARGET_EXPRs with
	TARGET_EXPR_NO_ELIDE flag set unless *expr_p is INIT_EXPR.

	* cp-tree.h (CONSTRUCTOR_PLACEHOLDER_BOUNDARY): Define.
	(find_placeholder): Declare.
	* tree.c (struct replace_placeholders_t): Add exp member.
	(replace_placeholders_r): Don't walk into ctors with
	CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set, unless they are equal to
	d->exp.  Replace PLACEHOLDER_EXPR with unshare_expr (x) rather than x.
	(replace_placeholders): Initialize data.exp.
	(find_placeholders_r, find_placeholders): New functions.
	* typeck2.c (process_init_constructor_record,
	process_init_constructor_union): Set CONSTRUCTOR_PLACEHOLDER_BOUNDARY
	if adding NSDMI on which find_placeholder returns true.
	* call.c (build_over_call): Don't call replace_placeholders here.
	* cp-gimplify.c (cp_genericize_r): Set TARGET_EXPR_NO_ELIDE on
	TARGET_EXPRs with CONSTRUCTOR_PLACEHOLDER_BOUNDARY set on
	TARGET_EXPR_INITIAL.
	(cp_fold): Copy over CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit to new
	ctor.

	* g++.dg/cpp1y/pr79937-1.C: New test.
	* g++.dg/cpp1y/pr79937-2.C: New test.
	* g++.dg/cpp1y/pr79937-3.C: New test.
	* g++.dg/cpp1y/pr79937-4.C: New test.
	* g++.dg/cpp1y/pr82410.C: New test.

From-SVN: r258593