[Ada] Crash on expression function as completion, with implicit dereference

[Ada] Crash on expression function as completion, with implicit dereference

An implicit dereference freezes the corresponding designated type. Most
implicit dereferences are made explicit during expansion, but this is not the
case for a dispatching call where the the controlling parameter and the
corresponding controlling argument are access to a tagged type. In that case,
to enforce the rule that an expression function that is a completion freezes
type references within, we must locate controlling arguments of an access type
and freeze explicitly the corresponding designated type.

2018-01-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch6.adb (Freeze_Expr_Types): If an access value is the
	controlling argument of a dispatching call. freeze the corresponding
	designated type.

gcc/testsuite/

	* gnat.dg/expr_func3.adb, gnat.dg/expr_func3.ads: New testcase.

From-SVN: r256507