Re: Small grammar, long compilation time

On 10/30/2017 09:28 AM, Søren Enevoldsen wrote:
[snip]
> I submitted a pull request with some strings that should parse ok (they 
> do here). 
Thanks :)
> I had to turn off BOOST_SPIRIT_X3_DEBUG in order to compile 
> the code in the link you sent.
That's strange.  I just compiled&ran without problem, and it showed
the output of the debug trace, part of which is:

--{--cut here--
> /home/evansl/dwnlds/llvm/5.0/prebuilt/clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/clang++ -c -O0 -gdwarf-2 -stdlib=libc++  -std=c++1z -ftemplate-backtrace-limit=0 -fdiagnostics-show-template-tree -fno-elide-type -fmacro-backtrace-limit=0     -I/home/evansl/prog_dev/boost/releases/ro/boost_1_65_1/sandbox/pull_requests/context_debug_fix.fork/spirit/include -I/home/evansl/prog_dev/boost/releases/ro/boost_1_65_1 -I/home/evansl/prog_dev/boost/sandbox/lje/non_variadic_templates -DBOOST_SPIRIT_X3_EXPERIMENTAL_GET_RHS_NS=1 -DBOOST_SPIRIT_X3_EXPERIMENTAL_GET_RHS_CRTP=0 -DBOOST_SPIRIT_X3_EXPERIMENTAL_ATTR_XFORM_IN_RULE=1     -ftemplate-depth=200  wccs_parser.cpp -MMD -o /tmp/build/clangxx5_0_pkg/boost/releases/ro/boost_1_65_1/sandbox/pull_requests/context_debug_fix.fork/spirit/workbench/x3/rec_ex_orig/wccs_parser.o 
> /home/evansl/dwnlds/llvm/5.0/prebuilt/clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/clang++ -stdlib=libc++    /tmp/build/clangxx5_0_pkg/boost/releases/ro/boost_1_65_1/sandbox/pull_requests/context_debug_fix.fork/spirit/workbench/x3/rec_ex_orig/wccs_parser.o   -o /tmp/build/clangxx5_0_pkg/boost/releases/ro/boost_1_65_1/sandbox/pull_requests/context_debug_fix.fork/spirit/workbench/x3/rec_ex_orig/wccs_parser.exe
> /tmp/build/clangxx5_0_pkg/boost/releases/ro/boost_1_65_1/sandbox/pull_requests/context_debug_fix.fork/spirit/workbench/x3/rec_ex_orig/wccs_parser.exe 
> <process>
>   <try>0</try>
>   <choice>
>     <try>0</try>
>     <composition>
>       <try>0</try>
>       <actionPrefix>
>         <try>0</try>
>         <N11wccs_parser22AstActionPrefixProcessE>
>           <try>0</try>
>           <N11wccs_parser9AstActionE>
>             <try>0</try>
>             <fail/>
>           </N11wccs_parser9AstActionE>
>           <fail/>
>         </N11wccs_parser22AstActionPrefixProcessE>
>         <renaming>
>           <try>0</try>
>           <restriction>
>             <try>0</try>
>             <primitive>
>               <try>0</try>
>               <N11wccs_parser14AstNullProcessE>
>                 <try>0</try>
> 

--}--cut here--

Hence, I'm guessing I've not pushed on my local changes to the remote.  I'll
try to figure out what and correct.
[snip]
> 
> But just to be clear, it is compilation time that is the problem, not 
> any particular input string. 

I understand.  However, I wanted to see it actually run.  In addition,
I wanted to see the changes I just made, worked. That's one reason for
the #define BOOST_SPIRIT_X3_DEBUG.

> I have been trying to simplify the case. 
> Whenever I eliminate a rule in the "tower"/hierarchy of rules   Process 
> ::= choice and choice -> composition -> renaming -> restriction -> 
> primitive, where we have the rule Process ::= choice again in 
> parenthesis, the compilation time becomes practical again. I would 
> assume such a hierarchy is not unusual for expressions. A naive guess is 
> that it is somehow connected to the use of AstAnyProcess and the 
> x3::forward_ast. But I have been unable to simplify the grammar without 
> unexploding the compile time.

Thanks for trying.  This make me suspect that this is an important test
case because still, despite hours trying to understand and modify the
code, I'm still don't understand it very well.  I suspect pinning down
why this is happening my help me (and others) understand the code 
better.  Of course 2 eyes on the problem is more helpful than just
one; so, I hope you keep trying with me to understand the root cause
of this problem.
> 
> - Søren
> 
> 
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