[Ada] Expand range checks in the front end rather than in gigi

[Arnaud Charlet <charlet at adacore dot com>]

This set of changes adds generation of scalar range checks to the GNAT
front end (gnat1) that were being done by gigi. Some range checks were
already being done in gnat1 (such as index checks and checks on assignment),
but many cases were passed on to gigi. Note that the code in gigi for doing
range checks when the Do_Range_Check flag is set is retained (possibly to
be reenabled under control of a switch to be added later), but the
Do_Range_Check flag is now generally reset by the front end after
it generates any range checks. There are still a few cases involving
fixed- and floating-point conversions where the check is still done
by gigi.

No additional test: range checks are tested extensively by ACATS tests.

Tested on x86_64-pc-linux-gnu, committed on trunk

2009-07-07  Gary Dismukes  <dismukes@adacore.com>

	* checks.adb (Generate_Range_Check): Replace type conversions with
	unchecked conversions to support the case of performing range checks
	on Enum'Val (permits integer values to be converted to enumeration).

	* exp_attr.adb (Expand_N_Attribute_Reference, cases Attribute_Pred,
	Attribute_Succ): Set Do_Range_Check to False before calling
	Expand_Pred_Succ, to prevent gigi from generating any range checks.
	(Expand_N_Attribute_Reference, case Attribute_Val):
	Generate a range check when needed (and set Do_Range_Check to False).

	* exp_ch3.adb (Expand_N_Object_Declaration): Generate a range check on
	scalar object initialization if needed.

	* exp_ch4.adb (Expand_Allocator_Expression): Generate range checks
	when needed on scalar allocators.
	(Expand_N_Qualified_Expression): Generate range check when needed.
	(Expand_N_Slice): Remove call to Enable_Range_Check on slice ranges.
	Checks on slice ranges handled in Resolve_Slice.

	* exp_ch5.adb (Expand_N_Assignment_Statement): Generate a range check,
	when needed, for all scalar assignments, not just discrete.
	(Expand_Simple_Function_Return): Resolve the conversion created for a
	scalar function return so that the conversion will get expanded to
	generate a possible constraint check.

	* exp_ch6.adb (Expand_Actuals): Call Add_Call_By_Copy_Code for out and
	in out scalar actuals when subtypes don't match, to ensure generation
	of return checks (and set Do_Range_Check to False).
	(Expand_Call): Uncomment code to perform range checks, but make it apply
	only to in and in out parameters (checks on parameter returns are
	handled in Expand_Actuals). If a scalar actual for a call to a derived
	subprogram is marked as needing a range check, peform it here (and set
	Do_Range_Check to False).

	* sem_aggr.adb (Resolve_*_Aggregate.Resolve_Aggr_Expr): Generate a
	range check on scalar component associations when needed.

	* sem_eval.adb (In_Subrange_Of): Return False when the first type has
	infinities but the second type does not, as these aren't compatible
	floating-point types.

	* sem_res.adb (Resolve_Slice): In the case where the prefix of the
	slice is itself a slice, pick up the Etype of the prefix. This handles
	the case where the prefix was an Image attribute expanded to a slice,
	and ensures that we get the subtype with the slice constraint rather
	than the unconstrained subbtype of the 'Image.

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