[Emacs-diffs] master b76389f 2/7: Don’t over-align if WIDE_EMACS_INT

[Paul Eggert]

branch: master
commit b76389f22070bb61811eeea41635640d31115fd9
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    Don’t over-align if WIDE_EMACS_INT
    
    * src/lisp.h (GCALIGNED_UNION): New macro.
    (struct Lisp_Symbol, union vectorlike_header)
    (struct Lisp_Cons, struct Lisp_String):
    Use it to avoid possible over-alignment if !USE_LSB_TAG.
---
 src/lisp.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/lisp.h b/src/lisp.h
index c5af4fa..5b296cd 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -229,7 +229,7 @@ extern bool suppress_checking EXTERNALLY_VISIBLE;
    USE_LSB_TAG not only requires the least 3 bits of pointers returned by
    malloc to be 0 but also needs to be able to impose a mult-of-8 alignment
    on some non-GC Lisp_Objects, all of which are aligned via
-   'char alignas (GCALIGNMENT) gcaligned;' inside a union.  */
+   GCALIGNED_UNION at the end of a union.  */
 
 enum Lisp_Bits
   {
@@ -277,6 +277,12 @@ DEFINE_GDB_SYMBOL_END (VALMASK)
 error !;
 #endif
 
+#if USE_LSB_TAG
+# define GCALIGNED_UNION char alignas (GCALIGNMENT) gcaligned;
+#else
+# define GCALIGNED_UNION
+#endif
+
 /* Lisp_Word is a scalar word suitable for holding a tagged pointer or
    integer.  Usually it is a pointer to a deliberately-incomplete type
    'union Lisp_X'.  However, it is EMACS_INT when Lisp_Objects and
@@ -776,7 +782,7 @@ struct Lisp_Symbol
       /* Next symbol in obarray bucket, if the symbol is interned.  */
       struct Lisp_Symbol *next;
     } s;
-    char alignas (GCALIGNMENT) gcaligned;
+    GCALIGNED_UNION
   } u;
 };
 verify (alignof (struct Lisp_Symbol) % GCALIGNMENT == 0);
@@ -890,7 +896,7 @@ union vectorlike_header
         Current layout limits the pseudovectors to 63 PVEC_xxx subtypes,
         4095 Lisp_Objects in GC-ed area and 4095 word-sized other slots.  */
     ptrdiff_t size;
-    char alignas (GCALIGNMENT) gcaligned;
+    GCALIGNED_UNION
   };
 verify (alignof (union vectorlike_header) % GCALIGNMENT == 0);
 
@@ -1250,7 +1256,7 @@ struct Lisp_Cons
        struct Lisp_Cons *chain;
       } u;
     } s;
-    char alignas (GCALIGNMENT) gcaligned;
+    GCALIGNED_UNION
   } u;
 };
 verify (alignof (struct Lisp_Cons) % GCALIGNMENT == 0);
@@ -1372,7 +1378,7 @@ struct Lisp_String
       unsigned char *data;
     } s;
     struct Lisp_String *next;
-    char alignas (GCALIGNMENT) gcaligned;
+    GCALIGNED_UNION
   } u;
 };
 verify (alignof (struct Lisp_String) % GCALIGNMENT == 0);