[gcc r10-9428] Fix ICE on atomic enumeration type with LTO

[Eric Botcazou]

https://gcc.gnu.org/g:4a068491e12ec39860ac55f4e86734306de47805

commit r10-9428-g4a068491e12ec39860ac55f4e86734306de47805
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Wed Mar 10 12:04:25 2021 +0100

    Fix ICE on atomic enumeration type with LTO
    
    This is a strange regression whereby an enumeration type declared as
    atomic (or volatile) incorrectly triggers the ODR machinery for its
    values in LTO mode.
    
    gcc/ada/
            * gcc-interface/decl.c (gnat_to_gnu_entity): Build a TYPE_STUB_DECL
            for the main variant of an enumeration type declared as volatile.
    gcc/testsuite/
            * gnat.dg/specs/lto25.ads: New test.

Diff:
---
 gcc/ada/gcc-interface/decl.c          |  4 ++++
 gcc/testsuite/gnat.dg/specs/lto25.ads | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index fb0042369c9..300f7c04b0c 100644
--- a/gcc/ada/gcc-interface/decl.c
+++ b/gcc/ada/gcc-interface/decl.c
@@ -4682,6 +4682,10 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	  const int quals
 	    = TYPE_QUAL_VOLATILE
 	      | (Is_Atomic_Or_VFA (gnat_entity) ? TYPE_QUAL_ATOMIC : 0);
+	  /* This is required by free_lang_data_in_type to disable the ODR.  */
+	  if (TREE_CODE (gnu_type) == ENUMERAL_TYPE)
+	    TYPE_STUB_DECL (gnu_type)
+	      = create_type_stub_decl (TYPE_NAME (gnu_type), gnu_type);
 	  gnu_type = change_qualified_type (gnu_type, quals);
 	}
 
diff --git a/gcc/testsuite/gnat.dg/specs/lto25.ads b/gcc/testsuite/gnat.dg/specs/lto25.ads
new file mode 100644
index 00000000000..89876b64a00
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/specs/lto25.ads
@@ -0,0 +1,12 @@
+-- { dg-do compile }
+-- { dg-options "-flto" { target lto } }
+
+package Lto25 is
+
+  type Enum is (One, Two, Three) with Atomic;
+
+  type Rec is record
+    E : Enum := One;
+  end record;
+
+end Lto25;