C++ support for -Wunused-but-set-variable

C++ support for -Wunused-but-set-variable

gcc/cp/ChangeLog:
	PR 18624
	* cp-tree.h (mark_exp_read, mark_rvalue_use, mark_lvalue_use,
	mark_type_use): Declare ...
	* expr.c (mark_exp_read, mark_rvalue_use, mark_lvalue_use,
	mark_type_use): ... new fns.
	* typeck.c (cxx_sizeof_expr, cxx_alignof_expr): Call mark_type_use.
	(perform_integral_promotions): Call mark_rvalue_use.
	(cp_build_unary_op): Call mark_lvalue_use.
	(decay_conversion): Update comment. Call mark_lvalue.
	* decl.c (unused_but_set_errorcount): New variable.
	(poplevel): Issue -Wunused-but-set-variable diagnostics.
	(duplicate_decls): Merge DECL_READ_P flags.
	(start_cleanup_fn): Set DECL_READ_P flag.
	(finish_function): Issue -Wunused-but-set-parameter diagnostics.
	* tree.c (rvalue): Call mark_rvalue_use.
	* pt.c (convert_nontype_argument): Likewise.
	* semantics.c (finish_typeof, finish_decltype_type): Call
	mark_type_use.
	(finish_asm_stmt): Call mark_lvalue_use.
	(finish_expr_stmt): Call mark_exp_read.
	* call.c (convert_like_real) <ck_identity, ck_user>: Call
	mark_rvalue_use.
	(build_x_va_arg): Call mark_lvalue_use.
	(build_over_call): Call mark_type_use.
	* init.c (build_new, build_delete): Call mark_value_use.
	* rtti.c (build_typeid): Call mark_lvalue_use or mark_type_use.
	(build_dynamic_cast_1): call mark_lvalue_use or mark_rvalue_use.

gcc/testsuite/ChangeLog:
	PR 18624
	* g++.dg/warn/Wunused-7.C: Add dg-warning.
	* g++.dg/template/sfinae16.C: Likewise.
	* gcc.dg/Wunused-var-1.c: Moved to...
	* c-c++-common/Wunused-var-1.c: ...here. New test.
	* gcc.dg/Wunused-var-2.c: Moved to...
	* c-c++-common/Wunused-var-2.c: ...here. New test.
	* gcc.dg/Wunused-var-3.c: Moved to...
	* c-c++-common/Wunused-var-3.c: ...here. New test.
	* gcc.dg/Wunused-var-4.c: Moved to...
	* gcc.dg/Wunused-var-1.c: ... here.
	* gcc.dg/Wunused-var-5.c: Moved to...
	* c-c++-common/Wunused-var-4.c: ...here. New test.
	* gcc.dg/Wunused-var-7.c: Moved to...
	* c-c++-common/Wunused-var-5.c: ...here. New test.
	* gcc.dg/Wunused-var-6.c: Moved to...
	* gcc.dg/Wunused-var-2.c: ... here.
	* c-c++-common/Wunused-var-1.c: New test.
	* c-c++-common/Wunused-var-2.c: New test.
	* c-c++-common/Wunused-var-3.c: New test.
	* c-c++-common/Wunused-var-4.c: New test.
	* c-c++-common/Wunused-var-5.c: New test.
	* g++.dg/warn/Wunused-var-1.C: New test.
	* g++.dg/warn/Wunused-var-2.C: New test.
	* g++.dg/warn/Wunused-var-3.C: New test.
	* g++.dg/warn/Wunused-var-4.C: New test.
	* g++.dg/warn/Wunused-var-5.C: New test.
	* g++.dg/warn/Wunused-var-6.C: New test.
	* g++.dg/warn/Wunused-var-7.C: New test.
	* g++.dg/warn/Wunused-var-8.C: New test.
	* g++.dg/warn/Wunused-parm-1.C: New test.
	* g++.dg/warn/Wunused-parm-2.C: New test.
	* g++.dg/warn/Wunused-parm-3.C: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@159096 138bc75d-0d04-0410-961f-82ee72b054a4