[antlr-interest] Performance problem with $text in ANTLR 3.1

Richard Knox rich at dreambox.com
Thu Aug 23 10:58:36 PDT 2012


I've upgraded to ANTLR 3.4, and I'm still seeing the same problem. One
test with VisualVM showed us spending 126 sec. (78% of total time) in
TokenRewriteStream.getKindOfOps. The big time consumers came from usages
of $text. Some of this grammar is old and krufty. We may be using $text
gratuitously, but I didn't see these problems with ANTLR 3.0.1.

I may be able to mitigate this problem by avoiding use of $text. For
example the following code accounted for 58 seconds of the time we spent
in getKindOfOps:

regular_tokens
	:	WORD -> template(val={ cpp.Lookup($text) }) "<val>"
	|	INT_LITERAL
	|	STRING_LITERAL
	|	PROXY_START_LITERAL | PROXY_MIDDLE_LITERAL | PROXY_END_LITERAL
	|	punctuation
	;

I made the following change to use $WORD.text instead of text:

regular_tokens
	:	WORD -> template(val={ cpp.Lookup($WORD.text) }) "<val>"
	|	INT_LITERAL
	|	STRING_LITERAL
	|	PROXY_START_LITERAL | PROXY_MIDDLE_LITERAL | PROXY_END_LITERAL
	|	punctuation
	;

This dropped total time in getKindOfOpes from 126 sec to 37 sec.

Two questions:
1) Is $text known to be badly performing? Should we avoid its use wherever
possible?
2) What changed from ANTLR 3.0.1 to cause this dramatic slow down?

Thanks.

-rich



On 8/21/12 6:55 PM, "Jim Idle" <jimi at temporal-wave.com> wrote:

>Move to 3.4. String template is much faster. However I am not sure about
>your view of the performance traits; but go to 3.4 and then you will be
>in a space to start analysis properly. At 3.1 no one can really help.
>
>Jim
>
>On Aug 21, 2012, at 6:26 PM, Richard Knox <rich at dreambox.com> wrote:
>
>> I recently upgraded an ANTLR based application from ANTLR 3.0.1 to
>>ANTLR 3.1. Since doing this, our application has been running MUCH
>>slower. I did some profiling with VisualVM and found that we were
>>spending most of our time in TokenRewriteStream.getKindOfOps. We get
>>there when we reference $text from a grammar with options
>>output=template and rewrite=true. Are there known performance issues
>>with this scenario in ANTRL 3.1? Would I get better perf with a later
>>version? Any suggested work arounds? Thanks!
>> 
>> -rich
>> 
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