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

loic.lefevre at bnpparibas.com loic.lefevre at bnpparibas.com
Wed Dec 16 04:29:25 PST 2009


Hello Jimi,
First thanks for your reply.

As you said, yes I'm really trying to enforce parsing paths.

What I've tried so far:

- Use int comparison instead or String comparison => KO
- Replaced {...}?=> (gated semantic predicates) by {...}? (disambiguating 
semantic predicates) => OK the switch has now 152 labels

I'll maybe use a method call next time bu I think I'm just delaying the 
problem here.

Regards,
Loïc




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jimi at temporal-wave.com
Envoyé par : antlr-interest-bounces at antlr.org
15/12/2009 19:08

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






The predicates are likely being hoisted into other rules because of the 
construction of your grammar. Without seeing the whole grammar it is not 
really possible to advise you any further.
 
However, I can infer from your snippet here that you are trying to enforce 
parsing paths. Wherever possible you should let the parser gather just 
about anything that COULD be valid syntax, produce an AST, then verify the 
AST. As you have things, your tags rules will issue syntax errors such as 
‘xxx’ unexpected token. However, if you merge all the tags into the one 
rule, you can then walk the tree, check the message type, then see if the 
tags that were picked up are valid for that message type. You errors will 
then be of the form “The tag ‘xxx’ is not valid for message type 103”.
 
So basically, I think that perhaps you are going about the problem in the 
wrong way and hence you are seeing issues like this.
 
That said, ANTLR probably isn’t generating the most efficient code that it 
could, but for the moment that is what it does I am afraid. The real issue 
though is the way you have put your grammar together I think. With 290+ 
message types, taking the approach you have now really isn’t practical I 
think. With more knowledge of your project, perhaps I might modify my 
opinion of course.
 
Jim
 
 
 
From: antlr-interest-bounces at antlr.org 
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of 
loic.lefevre at bnpparibas.com
Sent: Tuesday, December 15, 2009 9:56 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] Strange "code too large" error since *very 
simple* gated semantic predicates
 

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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