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c++: revamp the support for variants

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The current approach was too adhoc: the symbols were not sufficiently
self-contained, in particular wrt memory management.  The "new"
guideline is the one that should have been followed from the start:
let the symbols handle themslves, instead of leaving their users to
it.  It was justified by the will to avoid gratuitious moves and
copies, but the current approach does not seem to be slower, yet it
will probably be simpler to adjust to support move semantics from
C++11.

The documentation says that the %parse-param are available from the
%destructor.  In retrospect, that was a silly design decision, which
we can break for variants, as its a new feature.  It should be phased
out for non-variants too.

* data/variant.hh: A variant never knows if it stores something or
not, it is up to its users to store this information.
Yet, in parse.assert mode, make sure the empty/filled variants
are properly used.
(b4_symbol_constructor_define_): Don't call directly the symbol
constructor, to save a useless temporary.
* data/stack.hh (push): Steal the pushed value instead of duplicating
it.
This will simplify the callers of push, who handled this "move"
approach themselves.
* data/c++.m4 (basic_symbol): Let -1, as kind, denote the fact that
a symbol is empty.
This is needed for instance when shifting the lookahead: yyla
is given as argument to "push", and its value is then moved on
the stack.  But then yyla must be declared "empty" so that its
destructor won't be called.
(basic_symbol::move): New.
Move the responsibility of calling the destructor from yy_destroy
to ~basic_symbol in the case of variants.
* data/lalr1.cc (stack_symbol_type): Now a derived class from its
previous value, so that we can add a constructor from a symbol_type.
(by_state): State -1 means empty.
(yypush_): Factor, by calling one overload from the other one, and
using the new semantics of stack::push.
No longer reclaim by hand the memory from rhs symbols, since now
that we store objects with proper destructors, they will be reclaimed
automatically.
Conversely, be sure to delete yylhs.
* tests/c++.at (C++ Variant-based Symbols): New "unit" test for
symbols.
This commit is contained in:
Akim Demaille
2013-01-28 14:29:43 +01:00
parent 5f87211cb4
commit 97ae878ec3
5 changed files with 217 additions and 79 deletions
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96
data/lalr1.cc
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@@ -281,10 +281,18 @@ b4_location_define])])[
/// Copy constructor.
inline by_state (const by_state& other);
void move (by_state& that)
{
state = that.state;
that.state = -1;
}
/// The state.
state_type state;
/// The type (corresponding to \a state).
///
/// -1 when empty.
inline int type_get () const;
/// The type used to store the symbol type.
@@ -292,7 +300,16 @@ b4_location_define])])[
};
/// "Internal" symbol: element of the stack.
typedef basic_symbol<by_state> stack_symbol_type;
struct stack_symbol_type : basic_symbol<by_state>
{
/// Superclass.
typedef basic_symbol<by_state> super_type;
/// Construct an empty symbol.
stack_symbol_type ();
/// Steal the contents from \a sym to build this.
stack_symbol_type (state_type s, symbol_type& sym);
stack_symbol_type& operator= (const stack_symbol_type& that);
};
/// Stack type.
typedef stack<stack_symbol_type> stack_type;
@@ -512,7 +529,7 @@ m4_if(b4_prefix, [yy], [],
// by_state.
]b4_parser_class_name[::by_state::by_state ()
: state ()
: state (-1)
{}
]b4_parser_class_name[::by_state::by_state (const by_state& other)
@@ -526,7 +543,33 @@ m4_if(b4_prefix, [yy], [],
int
]b4_parser_class_name[::by_state::type_get () const
{
return yystos_[state];
return state == -1 ? -1 : yystos_[state];
}
inline
]b4_parser_class_name[::stack_symbol_type::stack_symbol_type ()
{}
inline
]b4_parser_class_name[::stack_symbol_type::stack_symbol_type (state_type s, symbol_type& sym)
: super_type (s]b4_locations_if([, sym.location])[)
{]b4_variant_if([[
]b4_symbol_variant([sym.type_get ()], [value], [move], [sym.value])],
[value = sym.value;])[
// sym is emptied.
sym.type = -1;
}
inline
]b4_parser_class_name[::stack_symbol_type&
]b4_parser_class_name[::stack_symbol_type::operator= (const stack_symbol_type& that)
{
state = that.state;]b4_variant_if([[
]b4_symbol_variant([that.type_get ()], [value], [copy], [that.value])],
[value = that.value;])[]b4_locations_if([
location = that.location;])[
return *this;
}
@@ -535,7 +578,7 @@ m4_if(b4_prefix, [yy], [],
]b4_parser_class_name[::yy_destroy_ (const char* yymsg, basic_symbol<Base>& yysym) const
{
if (yymsg)
YY_SYMBOL_PRINT (yymsg, yysym);
YY_SYMBOL_PRINT (yymsg, yysym);]b4_variant_if([], [
// User destructor.
int yytype = yysym.type_get ();
@@ -544,10 +587,7 @@ m4_if(b4_prefix, [yy], [],
]b4_symbol_foreach([b4_symbol_destructor])dnl
[ default:
break;
}]b4_variant_if([
// Type destructor.
b4_symbol_variant([[yytype]], [[yysym.value]], [[template destroy]])])[
}])[
}
#if ]b4_api_PREFIX[DEBUG
@@ -575,17 +615,8 @@ m4_if(b4_prefix, [yy], [],
void
]b4_parser_class_name[::yypush_ (const char* m, state_type s, symbol_type& sym)
{
if (m)
YY_SYMBOL_PRINT (m, sym);
]b4_variant_if(
[[
stack_symbol_type ss (]b4_join([s],
[sym.value], b4_locations_if([sym.location]))[);
]b4_symbol_variant([sym.type_get ()], [sym.value], [destroy], [])[;
yystack_.push (ss);
]],
[[ yystack_.push (stack_symbol_type (]b4_join([s],
[sym.value], b4_locations_if([sym.location]))[));]])[
stack_symbol_type t (s, sym);
yypush_ (m, t);
}
void
@@ -593,14 +624,7 @@ m4_if(b4_prefix, [yy], [],
{
if (m)
YY_SYMBOL_PRINT (m, s);
]b4_variant_if(
[[
stack_symbol_type ss (]b4_join([s.state],
[s.value], b4_locations_if([s.location]))[);
]b4_symbol_variant([s.type_get ()], [s.value], [destroy], [])[;
yystack_.push (ss);
]],
[ yystack_.push (s);])[
yystack_.push (s);
}
void
@@ -821,21 +845,6 @@ b4_dollar_popdef])[]dnl
YYERROR;
}
YY_SYMBOL_PRINT ("-> $$ =", yylhs);
]b4_variant_if([[
// Destroy the rhs symbols.
for (int i = 0; i < yylen; ++i)
// Destroy a variant whose value may have been swapped with
// yylhs.value (for instance if the action was "std::swap($$,
// $1)"). The value of yylhs.value (hence possibly one of these
// rhs symbols) depends on the default construction for this
// type. In the case of pointers for instance, no
// initialization is done, so the value is junk. Therefore do
// not try to report the value of symbols about to be destroyed
// in the debug trace, it's possibly junk. Hence yymsg = 0.
// Besides, that keeps exactly the same traces as with the other
// Bison skeletons.
yy_destroy_ (YY_NULL, yystack_[i]);]])[
yypop_ (yylen);
yylen = 0;
YY_STACK_PRINT ();
@@ -890,7 +899,8 @@ b4_dollar_popdef])[]dnl
goto yyerrorlab;]b4_locations_if([[
yyerror_range[1].location = yystack_[yylen - 1].location;]])b4_variant_if([[
/* $$ was initialized before running the user action. */
yy_destroy_ ("Error: discarding", yylhs);]])[
YY_SYMBOL_PRINT ("Error: discarding", yylhs);
yylhs.~stack_symbol_type();]])[
/* Do not reclaim the symbols of the rule whose action triggered
this YYERROR. */
yypop_ (yylen);