[gcc(refs/users/meissner/heads/ieee)] d: Fix assignment to anonymous union member corrupts sibling members in struct

[gcc(refs/users/meissner/heads/ieee)] d: Fix assignment to anonymous union member corrupts sibling members in struct

[Michael Meissner]

https://gcc.gnu.org/g:2691ffe6dbaffb704593dd6220178c28848b3855

commit 2691ffe6dbaffb704593dd6220178c28848b3855
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Mon Mar 16 23:53:20 2020 +0100

    d: Fix assignment to anonymous union member corrupts sibling members in struct
    
    gcc/d/ChangeLog:
    
            PR d/92309
            * types.cc (fixup_anonymous_offset): Don't set DECL_FIELD_OFFSET on
            anonymous fields.
    
    gcc/testsuite/ChangeLog:
    
            PR d/92309
            * gdc.dg/pr92309.d: New test.

Diff:
---
 gcc/d/ChangeLog                |  6 ++++++
 gcc/d/types.cc                 | 10 +++++++---
 gcc/testsuite/ChangeLog        |  5 +++++
 gcc/testsuite/gdc.dg/pr92309.d | 25 +++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/gcc/d/ChangeLog b/gcc/d/ChangeLog
index d9c7657eaac..ea43e3e82bd 100644
--- a/gcc/d/ChangeLog
+++ b/gcc/d/ChangeLog
@@ -1,3 +1,9 @@
+2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
+
+	PR d/92309
+	* types.cc (fixup_anonymous_offset): Don't set DECL_FIELD_OFFSET on
+	anonymous fields.
+
 2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
 
 	PR d/92216
diff --git a/gcc/d/types.cc b/gcc/d/types.cc
index 736f128422c..866da965b40 100644
--- a/gcc/d/types.cc
+++ b/gcc/d/types.cc
@@ -234,16 +234,20 @@ insert_aggregate_field (tree type, tree field, size_t offset)
 static void
 fixup_anonymous_offset (tree fields, tree offset)
 {
+  /* No adjustment in field offset required.  */
+  if (integer_zerop (offset))
+    return;
+
   while (fields != NULL_TREE)
     {
-      /* Traverse all nested anonymous aggregates to update their offset.
-	 Set the anonymous decl offset to its first member.  */
+      /* Traverse all nested anonymous aggregates to update the offset of their
+	 fields.  Note that the anonymous field itself is not adjusted, as it
+	 already has an offset relative to its outer aggregate.  */
       tree ftype = TREE_TYPE (fields);
       if (TYPE_NAME (ftype) && IDENTIFIER_ANON_P (TYPE_IDENTIFIER (ftype)))
 	{
 	  tree vfields = TYPE_FIELDS (ftype);
 	  fixup_anonymous_offset (vfields, offset);
-	  DECL_FIELD_OFFSET (fields) = DECL_FIELD_OFFSET (vfields);
 	}
       else
 	{
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a3820726772..0146f8d1759 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
+
+	PR d/92309
+	* gdc.dg/pr92309.d: New test.
+
 2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
 
 	PR d/92216
diff --git a/gcc/testsuite/gdc.dg/pr92309.d b/gcc/testsuite/gdc.dg/pr92309.d
new file mode 100644
index 00000000000..01ebc40d336
--- /dev/null
+++ b/gcc/testsuite/gdc.dg/pr92309.d
@@ -0,0 +1,25 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92309
+// { dg-do run { target hw } }
+// { dg-skip-if "needs gcc/config.d" { ! d_runtime } }
+
+union U
+{
+    struct
+    {
+        size_t a;
+        size_t b;
+        union
+        {
+            size_t c;
+            size_t d;
+        }
+    }
+}
+
+void main()
+{
+    U u;
+    assert(u.a == 0);
+    u.d = 1;
+    assert(u.a == 0);
+}