Re: [PATCH] c++: Allow IS_FAKE_BASE_TYPE for union types [PR114954]

[Jason Merrill]

On 5/6/24 02:32, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --

In some circumstances, unions can also have an __as_base type;

Hmm, even though unions can't be bases I guess that is needed for 
something like

union U {
  int i;
private:
  char c[5];
};

struct A {
  [[no_unique_address]] U u;
  char d;
};

static_assert (sizeof (A) == sizeof (U));

The patch is OK.

we need to make sure that IS_FAKE_BASE_TYPE correctly recognises this.

        PR c++/114954

gcc/cp/ChangeLog:

        * cp-tree.h (IS_FAKE_BASE_TYPE): Also apply to unions.

gcc/testsuite/ChangeLog:

        * g++.dg/modules/pr114954.C: New test.

Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
  gcc/cp/cp-tree.h                        |  2 +-
  gcc/testsuite/g++.dg/modules/pr114954.C | 14 ++++++++++++++
  2 files changed, 15 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/modules/pr114954.C

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 933504b4821..fa24217eb2b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -2616,7 +2616,7 @@ struct GTY(()) lang_type {
  
  /* True iff NODE is the CLASSTYPE_AS_BASE version of some type.  */
  #define IS_FAKE_BASE_TYPE(NODE)                                       \
-  (TREE_CODE (NODE) == RECORD_TYPE                             \
+  (RECORD_OR_UNION_TYPE_P (NODE)                               \
     && TYPE_CONTEXT (NODE) && CLASS_TYPE_P (TYPE_CONTEXT (NODE))       \
     && CLASSTYPE_AS_BASE (TYPE_CONTEXT (NODE)) == (NODE))
  
diff --git a/gcc/testsuite/g++.dg/modules/pr114954.C b/gcc/testsuite/g++.dg/modules/pr114954.C
new file mode 100644
index 00000000000..a9787140808
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr114954.C
@@ -0,0 +1,14 @@
+// PR c++/114954
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi main }
+
+export module main;
+
+template <int N>
+union U {
+private:
+  char a[N + 1];
+  int b;
+};
+
+U<4> p;