YAP would break when gc was called from portray:

always save arguments before calling plwrite with possible portray
 only do it for portray because plwrite may be called from unsafe environments
 make Slot machinery mainstream.


git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@637 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

C/exec.c

@@ -1447,8 +1447,11 @@ execute_goal(Term t, int nargs, SMALLUNSGN mod)
 #ifdef DEPTH_LIMIT
     DEPTH= B->cp_depth;
 #endif
-    YENV= ASP = B->cp_env;
-    ENV  = (CELL *)((B->cp_env)[E_E]);
+    /* ASP should be set to the top of the local stack when we
+       did the call */
+    ASP = B->cp_env;
+    /* YENV should be set to the current environment */
+    YENV = ENV  = (CELL *)((B->cp_env)[E_E]);
     B    = B->cp_b;
     SET_BB(B);
     HB = PROTECT_FROZEN_H(B);