exp_util.ads, [...]: This patch replaces a number of occurrences of explicit tests for N_Null with...

2007-08-14  Robert Dewar  <dewar@adacore.com>
	    Ed Schonberg  <schonberg@adacore.com>
	    Javier Miranda  <miranda@adacore.com>

	* exp_util.ads, exp_util.adb: 
	This patch replaces a number of occurrences of explicit tests for N_Null
	with calls to Known_Null. This improves tracking of null values, since
	Known_Null also catches null constants, and variables currently known to
	be null, so we get better tracking.
	(Ensure_Defined): create an itype reference only in the scope of the
	itype.
	(Side_Effect_Free): A selected component of an access type that
	denotes a component with a rep clause must be treated as not
	side-effect free, because if it is part of a linked structure its
	value may be affected by a renaming.
	(Expand_Subtype_From_Expr): For limited objects initialized with build
	in place function calls, do nothing; otherwise we prematurely introduce
	an N_Reference node in the expression initializing the object, which
	breaks the circuitry that detects and adds the additional arguments to
	the called function. Bug found working in the new patch for statically
	allocated dispatch tables.
	(Is_Library_Level_Tagged_Type): New subprogram.
	(Remove_Side_Effects): If the expression of an elementary type is an
	operator treat as a function call.
	(Make_Literal_Range): If the index type of the array is not integer, use
	attributes properly to compute the constraint on the resulting aggregate
	which is a string.

	* freeze.ads, freeze.adb (Freeze_Entity): If the entity is a
	class-wide type whose base type is an incomplete private type, leave
	class-wide type unfrozen so that freeze nodes can be generated
	properly at a later point.
	(Freeze_Entity, array case): Handle case of pragma Pack and component
	size attributre clause for same array.

From-SVN: r127419