[antlr-interest] Strange "code too large" error since *very simple* gated semantic predicates

loic.lefevre at bnpparibas.com loic.lefevre at bnpparibas.com
Tue Dec 15 09:56:08 PST 2009


Hello,
I'm encountering a strange antlr issue. I get a "code too large" error 
from the java compiler
on the DFA method specialStateTransition for the following grammar rule:

block_4_tags
        : {"103".equals(messageType)}?=> block_4_mt103_tags
        | {"202".equals(messageType)}?=> block_4_mt202_tags
        ;

The generated method has a switch with 339 labels.

Example of generated code:

        public int specialStateTransition(int s, IntStream _input) throws 
NoViableAltException {
            TokenStream input = (TokenStream)_input;
                int _s = s;
            switch ( s ) {
                    case 0 : 
                        int LA4_238 = input.LA(1);

 
                        int index4_238 = input.index();
                        input.rewind();
                        s = -1;
                        if ( (LA4_238==CAPITAL_LETTER) && 
(("202".equals(messageType)))) {s = 278;}

                        else if ( (LA4_238==DIGIT) && 
(("202".equals(messageType)))) {s = 279;}

 
                        input.seek(index4_238);
                        if ( s>=0 ) return s;
                        break;
                    case 1 : 
                        int LA4_321 = input.LA(1);

 
                        int index4_321 = input.index();
                        input.rewind();
                        s = -1;
                        if ( (LA4_321==DIGIT) && 
(("202".equals(messageType)))) {s = 342;}

                        else if ( (LA4_321==LETTER) && 
(("202".equals(messageType)))) {s = 312;}

                        else if ( (LA4_321==CAPITAL_LETTER) && 
(("202".equals(messageType)))) {s = 313;}

                        else if ( (LA4_321==SLASH) && 
(("202".equals(messageType)))) {s = 314;}

                        else if ( (LA4_321==SPACE) && 
(("202".equals(messageType)))) {s = 315;}

                        else if ( (LA4_321==ANTI_SLASH) && 
(("202".equals(messageType)))) {s = 316;}

                        else if ( (LA4_321==MINUS) && 
(("202".equals(messageType)))) {s = 317;}

                        else if ( (LA4_321==COLON) && 
(("202".equals(messageType)))) {s = 318;}

                        else if ( (LA4_321==LPAREN) && 
(("202".equals(messageType)))) {s = 319;}

                        else if ( (LA4_321==RPAREN) && 
(("202".equals(messageType)))) {s = 320;}

                        else if ( (LA4_321==DOT) && 
(("202".equals(messageType)))) {s = 321;}

                        else if ( (LA4_321==COMMA) && 
(("202".equals(messageType)))) {s = 322;}

                        else if ( (LA4_321==PLUS) && 
(("202".equals(messageType)))) {s = 323;}

                        else if ( (LA4_321==QUOTE) && 
(("202".equals(messageType)))) {s = 324;}

                        else if ( (LA4_321==QUESTION_MARK) && 
(("202".equals(messageType)))) {s = 325;}

 
                        input.seek(index4_321);
                        if ( s>=0 ) return s;
                        break;
...

As you can see the gated semantic predicates are propagated to almost 
every Java statements!

And this is *very* strange since the calling code is:

    public final void block_4_tags() throws RecognitionException {
        int block_4_tags_StartIndex = input.index();
        try {
            if ( state.backtracking>0 && alreadyParsedRule(input, 12) ) { 
return ; }
            // SWIFTMT.g:153:9: ({...}? => block_4_mt103_tags | {...}? => 
block_4_mt202_tags )
            int alt4=2;
            alt4 = dfa4.predict(input);
            switch (alt4) {
                case 1 :
                    // SWIFTMT.g:153:11: {...}? => block_4_mt103_tags
                    {
                    if ( !(("103".equals(messageType))) ) {
                        if (state.backtracking>0) {state.failed=true; 
return ;}
                        throw new FailedPredicateException(input, 
"block_4_tags", "\"103\".equals(messageType)");
                    }
                    if ( state.backtracking==0 ) {
                       System.out.println("Tags for MT103 chosen!"); 
                    }
 pushFollow(FOLLOW_block_4_mt103_tags_in_block_4_tags809);
                    block_4_mt103_tags();

                    state._fsp--;
                    if (state.failed) return ;

                    }
                    break;
                case 2 :
                    // SWIFTMT.g:154:11: {...}? => block_4_mt202_tags
                    {
                    if ( !(("202".equals(messageType))) ) {
                        if (state.backtracking>0) {state.failed=true; 
return ;}
                        throw new FailedPredicateException(input, 
"block_4_tags", "\"202\".equals(messageType)");
                    }
 pushFollow(FOLLOW_block_4_mt202_tags_in_block_4_tags824);
                    block_4_mt202_tags();

                    state._fsp--;
                    if (state.failed) return ;

                    }
                    break;

            }
        }
        catch (RecognitionException re) {
            reportError(re);
            recover(input,re);
        }
        finally {
            if ( state.backtracking>0 ) { memoize(input, 12, 
block_4_tags_StartIndex); }
        }
        return ;
    }

I would rather expect something like:

if( "103".equals(messageType) ) {
 pushFollow(FOLLOW_block_4_mt103_tags_in_block_4_tags809);
                    block_4_mt103_tags();

                    state._fsp--;
                    if (state.failed) return ;
} else
if( "202".equals(messageType) ) {
 pushFollow(FOLLOW_block_4_mt202_tags_in_block_4_tags824);
                    block_4_mt202_tags();

                    state._fsp--;
                    if (state.failed) return ;
} else { /* error check? */ }

and of course this DFA4 would never exist :o)

Is it currently possible?

Has anyone some workaround?

I'll also try int comparison (I'm lucky since these are numbers) but I've 
got more message types to test (290+).

Regards,
Loïc




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