[Bug target/65146] alignment of _Atomic structure member is not correct

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65146

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |uros at gcc dot gnu.org

--- Comment #21 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, are we talking about something like (no -Wpsabi here)
--- gcc/config/i386/i386.c.jj   2020-08-24 10:00:01.321258451 +0200
+++ gcc/config/i386/i386.c      2020-08-26 17:54:39.089468108 +0200
@@ -16487,7 +16487,11 @@ iamcu_alignment (tree type, int align)

   /* Intel MCU psABI specifies scalar types > 4 bytes aligned to 4
      bytes.  */
-  mode = TYPE_MODE (strip_array_types (type));
+  type = strip_array_types (type);
+  if (TYPE_ATOMIC (type))
+    return align;
+
+  mode = TYPE_MODE (type);
   switch (GET_MODE_CLASS (mode))
     {
     case MODE_INT:
@@ -16757,7 +16761,7 @@ ix86_minimum_alignment (tree exp, machin
   /* Don't do dynamic stack realignment for long long objects with
      -mpreferred-stack-boundary=2.  */
   if ((mode == DImode || (type && TYPE_MODE (type) == DImode))
-      && (!type || !TYPE_USER_ALIGN (type))
+      && (!type || (!TYPE_USER_ALIGN (type) && !TYPE_ATOMIC (type)))
       && (!decl || !DECL_USER_ALIGN (decl)))
     {
       gcc_checking_assert (!TARGET_STV);
@@ -20293,7 +20297,10 @@ x86_field_alignment (tree type, int comp
     return computed;
   if (TARGET_IAMCU)
     return iamcu_alignment (type, computed);
-  mode = TYPE_MODE (strip_array_types (type));
+  type = strip_array_types (type);
+  if (TYPE_ATOMIC (type))
+    return computed;
+  mode = TYPE_MODE (type);
   if (mode == DFmode || mode == DCmode
       || GET_MODE_CLASS (mode) == MODE_INT
       || GET_MODE_CLASS (mode) == MODE_COMPLEX_INT)
No idea whether we need the ix86_minimum_alignment change and about IAMCU I'll
defer to H.J., but the last hunk fixes something like #c1 or
struct A { char a; _Atomic long long b; };
struct B { char a; _Atomic double b; };
int a = __builtin_offsetof (struct A, b);
int b = __builtin_offsetof (struct B, b);
with -m32 for me.