ada: Clean up vanishing entity fields

Fix all the failures caused by enabling Check_Vanishing_Fields on
entities in all cases except the case of converting to or from E_Void.
But leave Check_Vanishing_Fields disabled by default (controlled by
-gnatd_v flag), because it might be too slow even for assertions-on
mode, and we should deal with the E_Void cases eventually.

The failures are fixed either by adding calls to Reinit_Field_To_Zero,
or by changing which entities have which fields.

Note that in a series of Reinit_Field_To_Zero calls, the optional
Old_Ekind parameter is only useful on the first such call.

gcc/ada/

	* atree.adb
	(Check_Vanishing_Fields): Disable the check for "root/base type
	only" fields. This is a bug fix -- if we're checking some subtype
	S, we don't want to reach over to the root or base type and
	Reinit_Field_To_Zero of that, thus modifying the field for lots of
	subtypes other than S. Disable in the to/from E_Void cases. Misc
	cleanup.
	* gen_il-gen-gen_entities.adb: Define First_Entity, Last_Entity,
	and Stored_Constraint for all type entities, because there are too
	many cases where Reinit_Field_To_Zero would otherwise be needed.
	In any case, it seems cleaner to have First_Entity and Last_Entity
	defined in the same entity kinds.
	* einfo.ads:
	(First_Entity, Last_Entity, Stored_Constraint): Update comments to
	reflect gen_il-gen-gen_entities.adb changes.
	(Lit_Hash): Add missing "[root type only]" comment.
	* exp_ch5.adb: Add Reinit_Field_To_Zero calls for vanishing
	fields.
	* sem_ch10.adb: Likewise.
	* sem_ch6.adb: Likewise.
	* sem_ch7.adb: Likewise.
	* sem_ch8.adb: Likewise.
	* sem_ch3.adb: Likewise. Also remove now-unnecessary
	Reinit_Field_To_Zero calls.

1 files changed, 11 insertions, 16 deletions

diff --git a/gcc/ada/einfo.ads b/gcc/ada/einfo.ads
index a200d63..878737c 100644
--- a/gcc/ada/einfo.ads
+++ b/gcc/ada/einfo.ads
@@ -1346,12 +1346,13 @@ package Einfo is
 --       find the first discriminant if discriminants are present.
 
 --    First_Entity
---       Defined in all entities which act as scopes to which a list of
---       associated entities is attached (blocks, class subtypes and types,
---       entries, functions, loops, packages, procedures, protected objects,
---       record types and subtypes, private types, task types and subtypes).
+--       Defined in all entities that act as scopes to which a list of
+--       associated entities is attached. This is defined in all [sub]types,
+--       including things like scalars that cannot have nested entities,
+--       which makes it more convenient to Mutate_Entity between type kinds.
 --       Points to a list of associated entities using the Next_Entity field
 --       as a chain pointer with Empty marking the end of the list.
+--       See also Last_Entity.
 
 --    First_Exit_Statement
 --       Defined in E_Loop entity. The exit statements for a loop are chained
@@ -3510,12 +3511,8 @@ package Einfo is
 --       statements whose value is not used.
 
 --    Last_Entity
---       Defined in all entities which act as scopes to which a list of
---       associated entities is attached (blocks, class subtypes and types,
---       entries, functions, loops, packages, procedures, protected objects,
---       record types and subtypes, private types, task types and subtypes).
---       Points to the last entry in the list of associated entities chained
---       through the Next_Entity field. Empty if no entities are chained.
+--       Defined for the same entity kinds as First_Entity. Last_Entity
+--       is the last entry in the list. Empty if no entities are chained.
 
 --    Last_Formal (synthesized)
 --       Applies to subprograms and subprogram types, and also in entries
@@ -3538,7 +3535,7 @@ package Einfo is
 --       field may be set as a result of a linker section pragma applied to the
 --       type of the object.
 
---    Lit_Hash
+--    Lit_Hash [root type only]
 --       Defined in enumeration types and subtypes. Non-empty only for the
 --       case of an enumeration root type, where it contains the entity for
 --       the generated hash function. See unit Exp_Imgv for full details of
@@ -4535,11 +4532,9 @@ package Einfo is
 --       share the same storage pool).
 
 --    Stored_Constraint
---       Defined in entities that can have discriminants (concurrent types
---       subtypes, record types and subtypes, private types and subtypes,
---       limited private types and subtypes and incomplete types). Points
---       to an element list containing the expressions for each of the
---       stored discriminants for the record (sub)type.
+--       Defined in type entities. Points to an element list containing the
+--       expressions for each of the stored discriminants, if any, for the
+--       (sub)type.
 
 --    Stores_Attribute_Old_Prefix
 --       Defined in constants, variables, and types which are created during