Re: move constructors

[John W. Eaton]

On 8/14/19 6:31 PM, Rik wrote:
> On 08/14/2019 02:43 PM, Rik wrote:

> > Just to get an idea, I modified the destructor in Array.h to
> >
> >     ~ArrayRep (void) {
> >         static long int n = 0;
> >         std::cerr << "~ArrayRep: " << ++n << "\n";
> >         delete [] data; }
> >
> > I find that running an average statement like "x = 1;" causes 40 
> > destructor calls.  That does seem excessive.

Yeah, that does seem like a lot.  Maybe it can be reduced, but first we 
have to know where they are happening and why.

> A similar experiment with modifying the destructor for octave_value_list 
> shows that we are creating/destroying a lot more of these then I think 
> is necessary given the complexity of the statements.  A simple function 
> call seems to require 9 octave_value_list objects.

I'm sure there's a lot of room for improvement.  I traced the calls to 
the destructors for the expression "sin(1);".  I found:

  * Three calls in tree_evaluator::convert_to_const_vector.  That is 
the function that takes the argument list object in the parse tree and 
converts it to an octave_value_list object.

  * Five calls in tree_evaluator::visit_index_expression.  Two of those 
are happening at the point of the call to the sin function, so probably 
inside the code that calls the function, not the visit_index_expression 
function itself.

  * One more call occurs inside the tree_evaluator::evaluate function 
when re-initializing the m_expr_result_value_list value.

> y =  2
> ~octave_value_list: 7814
> ~octave_value_list: 7815
> ~octave_value_list: 7816
> ~octave_value_list: 7817
> ~octave_value_list: 7818
> ~octave_value_list: 7819

Not that it's the only issue, but as far as I can tell, these are all 
due to calling the disp and display functions to print the result.  If I 
execute "y = 2;" to suppress printing, there are no calls to the 
octave_value_list destructor.

jwe