Re: member with constructor not allowed in union

[Paul Eggert]

> From: Akim Demaille <address@hidden>
> Date: 18 Mar 2002 11:31:23 +0100

> We cannot afford to put YYSTYPE (and actually YYLTYPE) into a union,
> as it makes it impossible for C++ users to use any useful structure
> in it.

OK, but (as you know) the code was broken at runtime, because it used
memcpy to copy the C++ objects when growing the stack, and bypassing
the constructors and destructors led to "pyrotechnical" behavior as
described in the Debian bug report at:
<http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=130914>

> would you handle the reversal in 1.3x?

I've installed the following patch in 1.3x.  It is not quite a
reversal, though, because it also fixes the "pyrotechnical" problem,
by disabling stack growth for C++ parsers that define YYSTYPE.
This should fix the compile-time problems that C++ users are
complaining about.  It should also fix the more-serious (and less
obvious) run-time problems with C++ parsers.

If I understand things correctly this change is not needed for the
1.4x version, as it has a separate C++ template.  But if I'm wrong
please let me know, so that I can install it there too.

This patch passes "make check" with Bison, but "make check" doesn't
have any C++ examples so I'd appreciate it if you C++ aficionados try
it out.


2002-03-18  Paul Eggert  <address@hidden>

        Fix the problem with union yyalloc and C++ (Debian bug 130914).

        * src/bison.simple (union yyalloc, YYSTACK_GAP_MAX, YYSTACK_BYTES,
        YYSTACK_RELOCATE): Do not define if yyoverflow is defined, or if
        this is a C++ parser and YYSTYPE or YYLTYPE has nontrivial
        constructors or destructors.
        (yymemcpy) [! defined YYSTACK_RELOCATE]: Do not define; not needed.
        (yyparse) [! defined YYSTACK_RELOCATE]: Do not relocate the stack.

        * src/reader.c (parse_union_decl): Define YYSTYPE_IS_TRIVIAL if we
        use our YYSTYPE.  It must be trivial, or our own union wouldn't be
        valid C++ anyway.
        (readgram): Define YYSTYPE_IS_TRIVIAL if it is int.
        (reader_output_yylsp): Define YYLTYPE_IS_TRIVIAL if we use our
        YYLTYPE.

Index: src/bison.simple
===================================================================
RCS file: /cvsroot/bison/bison/src/Attic/bison.simple,v
retrieving revision 1.53.2.19
diff -p -u -r1.53.2.19 bison.simple
--- src/bison.simple    25 Feb 2002 18:02:06 -0000      1.53.2.19
+++ src/bison.simple    18 Mar 2002 21:44:03 -0000
@@ -66,6 +66,12 @@
 #  define YYSTACK_ALLOC malloc
 #  define YYSTACK_FREE free
 # endif
+#endif /* ! defined (yyoverflow) || defined (YYERROR_VERBOSE) */
+
+
+#if (! defined (yyoverflow) \
+     && (! defined (__cplusplus) \
+        || (YYLTYPE_IS_TRIVIAL && YYSTYPE_IS_TRIVIAL)))
 
 /* A type that is properly aligned for any stack member.  */
 union yyalloc
@@ -109,7 +115,7 @@ union yyalloc
       }                                                                        
\
     while (0)
 
-#endif /* ! defined (yyoverflow) || defined (YYERROR_VERBOSE) */
+#endif
 
 
 #if ! defined (YYSIZE_T) && defined (__SIZE_TYPE__)
@@ -236,7 +242,7 @@ int yydebug;
 # define YYMAXDEPTH 10000
 #endif
 
-#if ! defined (yyoverflow) && ! defined (yymemcpy)
+#if defined (YYSTACK_RELOCATE) && ! defined (yymemcpy)
 # if __GNUC__ > 1              /* GNU C and GNU C++ define this.  */
 #  define yymemcpy __builtin_memcpy
 # else                         /* not GNU C or C++ */
@@ -504,6 +510,9 @@ yyparse (YYPARSE_PARAM_ARG)
        yyvs = yyvs1;
       }
 #else /* no yyoverflow */
+# ifndef YYSTACK_RELOCATE
+      goto yyoverflowlab;
+# else
       /* Extend the stack our own way.  */
       if (yystacksize >= YYMAXDEPTH)
        goto yyoverflowlab;
@@ -526,6 +535,7 @@ yyparse (YYPARSE_PARAM_ARG)
        if (yyss1 != yyssa)
          YYSTACK_FREE (yyss1);
       }
+# endif
 #endif /* no yyoverflow */
 
       yyssp = yyss + yysize - 1;
Index: src/reader.c
===================================================================
RCS file: /cvsroot/bison/bison/src/reader.c,v
retrieving revision 1.72.2.30
diff -p -u -r1.72.2.30 reader.c
--- src/reader.c        4 Mar 2002 16:59:51 -0000       1.72.2.30
+++ src/reader.c        18 Mar 2002 21:44:03 -0000
@@ -745,6 +745,7 @@ typedef union";
   const char *epilogue = "\
  yystype;\n\
 # define YYSTYPE yystype\n\
+# define YYSTYPE_IS_TRIVIAL 1\n\
 #endif\n";
 
   if (typed)
@@ -1617,12 +1618,16 @@ readgram (void)
       /* We used to use `unsigned long' as YYSTYPE on MSDOS,
          but it seems better to be consistent.
          Most programs should declare their own type anyway.  */
-      obstack_sgrow (&attrs_obstack,
-                          "#ifndef YYSTYPE\n#define YYSTYPE int\n#endif\n");
+      obstack_sgrow (&attrs_obstack, "\
+#ifndef YYSTYPE\n\
+# define YYSTYPE int\n\
+# define YYSTYPE_IS_TRIVIAL 1\n\
+#endif\n");
       if (defines_flag)
        obstack_sgrow (&defines_obstack, "\
 # ifndef YYSTYPE\n\
 #  define YYSTYPE int\n\
+#  define YYSTYPE_IS_TRIVIAL 1\n\
 # endif\n");
     }
 
@@ -2043,6 +2048,7 @@ typedef struct yyltype\n\
 } yyltype;\n\
 \n\
 # define YYLTYPE yyltype\n\
+# define YYLTYPE_IS_TRIVIAL 1\n\
 #endif\n\
 \n");
 }