re PR debug/55608 (Debug info quality regressions with file scope vars)

re PR debug/55608 (Debug info quality regressions with file scope vars)

	PR debug/55608
	* dwarf2out.c (tree_add_const_value_attribute): Call ggc_free (array)
	on failure.
	(resolve_one_addr): Fail if referenced STRING_CST hasn't been written.
	(string_cst_pool_decl): New function.
	(optimize_one_addr_into_implicit_ptr): New function.
	(resolve_addr_in_expr): Optimize DWARF location expression
	DW_OP_addr DW_OP_stack_value where DW_OP_addr refers to some variable
	which doesn't live in memory, but has DW_AT_location or
	DW_AT_const_value, or refers to a string literal, into
	DW_OP_GNU_implicit_pointer.
	(optimize_location_into_implicit_ptr): New function.
	(resolve_addr): If removing DW_AT_location of a variable because
	it was DW_OP_addr of address of the variable, but the variable doesn't
	live in memory, try to emit const value attribute for the initializer.

From-SVN: r196886