From: Mark Wooding <mdw@distorted.org.uk>
Date: Sun, 30 Aug 2015 09:58:38 +0000 (+0100)
Subject: src/: Stuff vtable structures into a union.
X-Git-Url: https://git.distorted.org.uk/~mdw/sod/commitdiff_plain/c2438e62e7c3cf1b7006522cef61e8c6f797600b

src/: Stuff vtable structures into a union.

For the same reason that ichains are collected into a union: to force
the compiler's hand into getting the various members to overlap in the
common prefixes.

This doesn't affect day-to-day use, but it does change the types of the
things which are actually exported.
---

diff --git a/src/builtin.lisp b/src/builtin.lisp
index 8b4407b..696bcf6 100644
--- a/src/builtin.lisp
+++ b/src/builtin.lisp
@@ -95,7 +95,7 @@ static void *~A__imprint(void *p)
 {
   struct ~A *sod__obj = p;
 
-  ~:{sod__obj->~A.~A._vt = &~A;~:^~%  ~}
+  ~:{sod__obj->~A.~A._vt = &~A.~A;~:^~%  ~}
   return (p);
 }~2%"
 	    class
@@ -105,7 +105,8 @@ static void *~A__imprint(void *p)
 			     (tail (ichain-tail ichain)))
 			(list (sod-class-nickname head)
 			      (sod-class-nickname tail)
-			      (vtable-name class head))))
+			      (vtable-name class head)
+			      (sod-class-nickname tail))))
 		    (ilayout-ichains ilayout)))))
 
 (define-class-slot "init" (class stream)
diff --git a/src/class-output.lisp b/src/class-output.lisp
index 2ab6363..eb5bc26 100644
--- a/src/class-output.lisp
+++ b/src/class-output.lisp
@@ -296,11 +296,23 @@
 			 struct ~A {~%"
 		 (vtable-struct-tag chain-tail chain-head)))
 	((class :vtable chain-head :end)
-	 (format stream "};~2%"))))
+	 (format stream "};~2%")
+	 (format stream "/* Union of equivalent superclass vtables. */~@
+			 union ~A {~@
+			 ~:{  struct ~A ~A;~%~}~
+			 };~2%"
+		 (vtable-union-tag chain-tail chain-head)
+
+		 ;; As for the ichain union, make sure the most specific
+		 ;; class is first.
+		 (mapcar (lambda (super)
+			   (list (vtable-struct-tag super chain-head)
+				 (sod-class-nickname super)))
+			 (sod-class-chain chain-tail))))))
     (sequence-output (stream sequencer)
       ((class :vtable-externs)
-       (format stream "~@<extern const struct ~A ~2I~_~A__vtable_~A;~:>~%"
-	       (vtable-struct-tag chain-tail chain-head)
+       (format stream "~@<extern const union ~A ~2I~_~A__vtable_~A;~:>~%"
+	       (vtable-union-tag chain-tail chain-head)
 	       class (sod-class-nickname chain-head))))))
 
 (defmethod hook-output progn ((vtmsgs vtmsgs) (reason (eql :h)) sequencer)
@@ -470,12 +482,12 @@ const struct ~A ~A__classobj = {~%"
 		   (class :vtables :end))
       ((class :vtable chain-head :start)
        (format stream "/* Vtable for ~A chain. */~@
-		       const struct ~A ~A = {~%"
+		       const union ~A ~A = { {~%"
 	       chain-head
-	       (vtable-struct-tag chain-tail chain-head)
+	       (vtable-union-tag chain-tail chain-head)
 	       (vtable-name class chain-head)))
       ((class :vtable chain-head :end)
-       (format stream "};~2%")))))
+       (format stream "} };~2%")))))
 
 (defmethod hook-output progn ((cptr class-pointer)
 			      (reason (eql :c))
@@ -592,8 +604,10 @@ const struct ~A ~A__classobj = {~%"
 		   (*instance-class* :object chain-head :vtable)
 		   (*instance-class* :object chain-head :ichain :end))
       ((*instance-class* :object chain-head :vtable)
-       (format stream "      &~A__vtable_~A,~%"
-	       class (sod-class-nickname chain-head))))))
+       (format stream "      /* ~17@A = */ &~A.~A,~%"
+	       "_vt"
+	       (vtable-name class chain-head)
+	       (sod-class-nickname chain-tail))))))
 
 (defgeneric find-class-initializer (slot class)
   (:method ((slot effective-slot) (class sod-class))
diff --git a/src/class-utilities.lisp b/src/class-utilities.lisp
index f00bc64..0aec35a 100644
--- a/src/class-utilities.lisp
+++ b/src/class-utilities.lisp
@@ -189,6 +189,10 @@
 (defun vtmsgs-struct-tag (class super)
   (format nil "~A__vtmsgs_~A" class (sod-class-nickname super)))
 
+(export 'vtable-union-tag)
+(defun vtable-union-tag (class chain-head)
+  (format nil "~A__vtu_~A" class (sod-class-nickname chain-head)))
+
 (export 'vtable-struct-tag)
 (defun vtable-struct-tag (class chain-head)
   (format nil "~A__vt_~A" class (sod-class-nickname chain-head)))