Re: Small grammar, long compilation time

On 2017-10-27 14:41, Larry Evans wrote:
> On 10/26/2017 04:33 PM, Larry Evans wrote:
>> On 10/26/2017 09:03 AM, Søren Enevoldsen wrote:
>>> The following program takes about 10s to compile. However, the rule 
>>> currently used in parenProcess, 'nullProcess' should actually be 
>>> 'process'. However, when I make the change, compilation does not 
>>> finish. Instead CPU keeps spinning hot, and memory usage gradually 
>>> increases. Since it is a rather small grammar, I am guessing I am 
>>> doing something wrong. How do I make the grammar work then I correct 
>>> it by changing parenProcess to '(' > process > ')' ? (Note I cannot 
>>> reduce the number of rules between process and parenProcess for a 
>>> smaller example, since then the compile time immediately decreases).
>>>
>>> - Søren
>>>
>>> ====================================================================
>>>
>>> #include <boost/config/warning_disable.hpp>
>>> #include <boost/spirit/home/x3.hpp>
>>> #include <boost/spirit/home/x3/support/ast/variant.hpp>
>>> #include <boost/spirit/include/qi_char_class.hpp>
>>> #include <boost/fusion/include/adapt_struct.hpp>
>> [snip]
>>> x3::rule<struct processRule, AstAnyProcess> process{"process"};
>>>
>>> ///  Here be compile time dragons.
>>> auto const parenProcess = '(' > nullProcess > ')';
>>>
>>> auto const primitive = rule<AstAnyProcess>("primitive")
>>>      = parenProcess
>>>      | nullProcess
>>>      | constant;
>> [snip]
>> With this "convenience" change:
>>
>> #define USE_PROCESS_IN_PAREN
>> auto const parenProcess
>>    = '('
>> #ifdef USE_PROCESS_IN_PAREN
>>    ///  Here be compile time dragons.
>>    > process
>> #else
>>    > nullProcess
>> #endif
>>    > ')'
>>    ;
>>
>> and when compiled, it did take more than 10s (way more)
>> and I did see my memory use go up and 100% of some of
>> my cpu's.  However, when the get_rhs branch of a spirit
>> fork here:
>>
>> https://github.com/cppljevans/spirit/tree/get_rhs
>>
>> was -I included in front of the standard boost,
>> it compiled in a flash.
>>
>> This problem has been reported before; however, I've
>> been advised that it needs more documentation before
>> submitting it as a pull request.  I'm working slowly
>> on that.
>>
>> HTH.
>>
>> -regards,
>> Larry
>
> If you limit the instantiation depth to 200, you can
> get some idea of why it fails as shown in the attached.
> In brief, the context is being repeatedly augmented
> by the make_unique_context leading to the excessive
> instantiations.  The get_rhs branch avoids that
> repeated call to make_unique_context.
>
> -regards,
> Larry
>
>
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Thanks for the explanation and pointers Larry. But I am not sure what is 
happening for me.

I am using GCC 7.2.0 and compile using:
g++ wccs_parser.cpp -Wall -pedantic -O2 -march=x86-64 -std=c++17 -m64 
-I. -flto=4 -static-libgcc -static-libstdc++ -ljemalloc -o wccs_parser

A. Compiling without the equivalent of "USE_PROCESS_IN_PAREN" takes ~14s 
and ~930MB (maximum resident).

1. I clone your repo into ~/spirit
2. I add ~/spirit to very front of my CPLUS_INCLUDE_PATH . The full 
boost package (1.65.1) is very last. In fact these are the only two 
paths there.
3. I compile again and it takes ~15s and ~925MB.

I am quite sure it now uses your ~/spirit because now I get a pragma 
warning from the original boost (which I did not get before):

/home/soren/spirit/include/boost/spirit/home/x3/nonterminal/rule.hpp:23:19: 
note: #pragma message: not(BOOST_SPIRIT_ATTR_XFORM_IN_RULE)
    #pragma message "not(BOOST_SPIRIT_ATTR_XFORM_IN_RULE)"
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/soren/spirit/include/boost/spirit/home/x3/nonterminal/rule.hpp:28:19: 
note: #pragma message: not(BOOST_SPIRIT_GET_RHS_CRTP)
    #pragma message "not(BOOST_SPIRIT_GET_RHS_CRTP)"

And I can still not compile with "USE_PROCESS_IN_PAREN".

- Søren

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