[Ada] Fix crash on declaration of overaligned array with constraints

["Marc Poulhiès" <poulhies@adacore.com>]

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The semantic analyzer was setting the Is_Constr_Subt_For_UN_Aliased flag on
the actual subtype of the object, which is incorrect because the nominal
subtype is constrained.  This also adjusts a recent related change.

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

gcc/ada/

	* exp_util.adb (Expand_Subtype_From_Expr): Check for the presence
	of the Is_Constr_Subt_For_U_Nominal flag instead of the absence
	of the Is_Constr_Subt_For_UN_Aliased flag on the subtype of the
	expression of an object declaration before reusing this subtype.
	* sem_ch3.adb (Analyze_Object_Declaration): Do not incorrectly
	set the Is_Constr_Subt_For_UN_Aliased flag on the actual subtype
	of an array with definite nominal subtype.  Remove useless test.

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diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -5732,14 +5732,17 @@ package body Exp_Util is
       then
          if Is_Itype (Exp_Typ)
 
-           --  If Exp_Typ was created for a previous declaration whose nominal
-           --  subtype is unconstrained, and that declaration is aliased,
-           --  we need to generate a new subtype, because otherwise the
-           --  Is_Constr_Subt_For_U_Nominal flag will be set on the wrong
-           --  subtype, causing failure to detect non-statically-matching
-           --  subtypes on 'Access of the previously-declared object.
-
-           and then not Is_Constr_Subt_For_UN_Aliased (Exp_Typ)
+           --  When this is for an object declaration, the caller may want to
+           --  set Is_Constr_Subt_For_U_Nominal on the subtype, so we must make
+           --  sure that either the subtype has been built for the expression,
+           --  typically for an aggregate, or the flag is already set on it;
+           --  otherwise it could end up being set on the nominal constrained
+           --  subtype of an object and thus later cause the failure to detect
+           --  non-statically-matching subtypes on 'Access of this object.
+
+           and then (Nkind (N) /= N_Object_Declaration
+                      or else Nkind (Exp) = N_Aggregate
+                      or else Is_Constr_Subt_For_U_Nominal (Exp_Typ))
          then
             --  Within an initialization procedure, a selected component
             --  denotes a component of the enclosing record, and it appears as


diff --git a/gcc/ada/sem_ch3.adb b/gcc/ada/sem_ch3.adb
--- a/gcc/ada/sem_ch3.adb
+++ b/gcc/ada/sem_ch3.adb
@@ -4770,20 +4770,13 @@ package body Sem_Ch3 is
          if not Is_Entity_Name (Object_Definition (N)) then
             Act_T := Etype (E);
             Check_Compile_Time_Size (Act_T);
-
-            if Aliased_Present (N) then
-               Set_Is_Constr_Subt_For_UN_Aliased (Act_T);
-            end if;
          end if;
 
          --  When the given object definition and the aggregate are specified
          --  independently, and their lengths might differ do a length check.
          --  This cannot happen if the aggregate is of the form (others =>...)
 
-         if not Is_Constrained (T) then
-            null;
-
-         elsif Nkind (E) = N_Raise_Constraint_Error then
+         if Nkind (E) = N_Raise_Constraint_Error then
 
             --  Aggregate is statically illegal. Place back in declaration