This is a regression present on all active branches: the compiler enters an
infinite recursion when it is generating the initialization procedure of an
unchecked union type with a representation clause, because the internal layout
it has done for it is problematic. This comes from a kludge added to support
aggregates for such types, so the fix is to further tweak this kludge.
Tested on x86-64/Linux, applied on all the active branches.
2026-02-28 Eric Botcazou <[email protected]>
PR ada/124285
* gcc-interface/decl.cc (components_to_record): Force a packed
layout for the innermost variant of an unchecked union type with
fixed part and full representation clause.
2026-02-28 Eric Botcazou <[email protected]>
* gnat.dg/specs/unchecked_union3.ads: New test.
--
Eric Botcazoudiff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
index 028fa0e5ea3..4ccc8d7a0e1 100644
--- a/gcc/ada/gcc-interface/decl.cc
+++ b/gcc/ada/gcc-interface/decl.cc
@@ -8513,7 +8513,7 @@ typedef struct vinfo
DEBUG_INFO is true if we need to write debug information about the type.
- IN_VARIANT is true if the componennt list is that of a variant.
+ IN_VARIANT is true if the component list is that of a variant.
FIRST_FREE_POS, if nonzero, is the first (lowest) free field position in
the outer record type down to this variant level. It is nonzero only if
@@ -8630,7 +8630,7 @@ components_to_record (Node_Id gnat_component_list, Entity_Id gnat_record_type,
tree gnu_union_type;
tree this_first_free_pos, gnu_variant_list = NULL_TREE;
bool union_field_needs_strict_alignment = false;
- bool innermost_variant_level = true;
+ bool innermost_of_unchecked_union = false;
auto_vec <vinfo_t, 16> variant_types;
vinfo_t *gnu_variant;
unsigned int variants_align = 0;
@@ -8679,15 +8679,19 @@ components_to_record (Node_Id gnat_component_list, Entity_Id gnat_record_type,
/* For an unchecked union with a fixed part, we need to compute whether
we are at the innermost level of the variant part. */
if (unchecked_union && gnu_field_list)
- for (variant = First_Non_Pragma (Variants (gnat_variant_part));
- Present (variant);
- variant = Next_Non_Pragma (variant))
- if (Present (Component_List (variant))
- && Present (Variant_Part (Component_List (variant))))
- {
- innermost_variant_level = false;
- break;
- }
+ {
+ innermost_of_unchecked_union = true;
+
+ for (variant = First_Non_Pragma (Variants (gnat_variant_part));
+ Present (variant);
+ variant = Next_Non_Pragma (variant))
+ if (Present (Component_List (variant))
+ && Present (Variant_Part (Component_List (variant))))
+ {
+ innermost_of_unchecked_union = false;
+ break;
+ }
+ }
/* We build the variants in two passes. The bulk of the work is done in
the first pass, that is to say translating the GNAT nodes, building
@@ -8734,17 +8738,17 @@ components_to_record (Node_Id gnat_component_list, Entity_Id gnat_record_type,
the outer variant, so as to flatten the rep-ed layout as much as
possible, the reason being that we cannot do any flattening when
a subtype statically selects a variant later on, for example for
- an aggregate. */
+ an aggregate; in that case, we force a packed layout because the
+ moved fields may overlap with packed bit-fields. */
has_rep
= components_to_record (Component_List (variant), gnat_record_type,
- NULL_TREE, gnu_variant_type, packed,
+ NULL_TREE, gnu_variant_type, packed ||
+ (all_rep && innermost_of_unchecked_union),
definition, !all_rep_and_size, all_rep,
unchecked_union, true, needs_xv_encodings,
true, this_first_free_pos,
(all_rep || this_first_free_pos)
- && !(unchecked_union
- && gnu_field_list
- && innermost_variant_level)
+ && !innermost_of_unchecked_union
? NULL : &gnu_rep_list);
/* Translate the qualifier and annotate the GNAT node. */
-- { dg-do compile }
with Interfaces;
package Unchecked_Union3 is
type T_CAN_ID is mod 2**29 with
Default_Value => 0,
Size => 29;
type T_Node_ID is mod 2**7 with
Size => 7,
Default_Value => 0;
type T_Message_Type_ID is new Interfaces.Unsigned_16;
type T_Service_Type_ID is new Interfaces.Unsigned_8;
type T_Priority is mod 2**5 with
Size => 5,
Default_Value => 0;
type T_Format_Selector is
(CAN_Fields,
DroneCAN_Fields);
type T_Frame_Selector is
(Message_Frame,
Anonymous_Frame,
Service_Frame);
type Unsigned_2 is mod 2**2 with
Size => 2,
Default_Value => 0;
type Unsigned_14 is mod 2**14 with
Size => 14,
Default_Value => 0;
type T_Header (Format_Selector : T_Format_Selector := DroneCAN_Fields;
Frame_Selector : T_Frame_Selector := Message_Frame) is record
case Format_Selector is
when CAN_Fields =>
CAN_ID : T_CAN_ID;
when DroneCAN_Fields =>
Source_Node_ID : T_Node_ID;
Service_Not_Message : Boolean := False;
Priority : T_Priority;
case Frame_Selector is
when Message_Frame =>
Message_Type_ID : T_Message_Type_ID;
when Anonymous_Frame =>
Message_Type_ID_Lower_Bits : Unsigned_2;
Discriminator : Unsigned_14;
when Service_Frame =>
Destination_Node_ID : T_Node_ID;
Request_Not_Response : Boolean := False;
Service_Type_ID : T_Service_Type_ID;
end case;
end case;
end record with
Unchecked_Union,
Size => 29;
for T_Header use record
CAN_ID at 0 range 0 .. 28;
Source_Node_ID at 0 range 0 .. 6;
Service_Not_Message at 0 range 7 .. 7;
Priority at 0 range 24 .. 28;
Message_Type_ID at 0 range 8 .. 23;
Message_Type_ID_Lower_Bits at 0 range 8 .. 9;
Discriminator at 0 range 10 .. 23;
Destination_Node_ID at 0 range 8 .. 14;
Request_Not_Response at 0 range 15 .. 15;
Service_Type_ID at 0 range 16 .. 23;
end record;
end Unchecked_Union3;
