[Ada] Improve compile-time evaluation of value ranges

[Ada] Improve compile-time evaluation of value ranges

2020-06-18  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* checks.adb (Compute_Range_For_Arithmetic_Op): New procedure to
	compute a range for an arithmetical operation extracted from...
	(Minimize_Eliminate_Overflows): ...here.  Call it.
	(Determine_Range_Cache_O): New cache for Original_Node nodes.
	(Determine_Range): Call Compute_Range_For_Arithmetic_Op for all
	arithmetic expressions. Use Attribute_Id in lieu of Attribute_Name
	for attributes. Add handling for Range_Length alongside Length.
	Add specific handling for Alignment, Bit, First_Bit, Last_Bit,
	Max_Size_In_Storage_Elements, Position, Bit_Position,
	Component_Size, Object_Size, Size, Value_Size, Descriptor_Size.
	(Enable_Overflow_Check): Omit the check for Abs and Minus if the
	operand cannot be the largest negative number.
	(Selected_Length_Checks): Use Pos for Number_Dimensions.
	* exp_attr.adb (Expand_N_Attribute_Reference): Move compile-time
	handling of Bit_Position, Descriptor_Size, First_Bit, Last_Bit
	and Position to...
	* sem_attr.adb (Eval_Attribute): ...here.  Move up Alignment for
	objects and use Compile_Time_Known_Attribute in this case too.