pre operator cannot be compiled

[fh77]

Here I'm not sure if its a bug.

The pre operator cannot be compiled if it is applied on a
variable, which does not change during the runtime
(in the sample the value of i1.el.val is always 12)

If the value is incremented the pre operator can be
compiled:

Here is the small sample:

block tst4B
  String k;   
  output ct i1;
  output ct i2;
  output ct i3;
  Boolean clock;
  Integer cntr;
  initial equation 
    cntr=0;
  equation
     clock = sample(0,0.1);
     i1.el.val=12;
     i2.el.val=pre(cntr)+2;
     i3.el.val=14;
    algorithm
     when clock then
        cntr:=cntr+1;
      end when;

    when (pre(i1.el.val)<> i1.el.val)   then 
      k:= f3(String(i1.el.val)+"abcdef185","eee1.txt");     
     end when; 

end tst4B;

type Int16 = Integer; 


record tstR
     Int16 val;
end tstR;

connector ct
  tstR el;
 end ct;

function f3 
   input String s2;
   input String s1;
   import Modelica.Utilities.Streams;
   output String s3; 
algorithm
    Streams.print(s1 + s2 + "xyz" ,"eee1.txt");
    s3:=s1+s2; 
end f3;

[Adrian Pop]

Hi,

If you add three curly braces before and after the code it will keep the formatting, like this:

  write some
  code here

[Martin Sjölund]

Ok, this is due to known variable eliminiation...

  tmp1023 = pre((modelica_integer) 12);

This means when we substitute i1.el.val=12, we also need to substitute pre(i1.el.val)=12 (maybe also der(i1.el.val) = 0). This would be good to do since further optimizations could be performed.

Adding Jens to the ticket :)

[Jens Frenkel]

Why not add the rule "pre(const) = const" to ExpressionSimplify.simplify

[Martin Sjölund]

I was considering doing that as well. It would be good if we changed simplify from bottom-up to top-down+bottom-up, since then we could also record if subexpressions are constant without traversing subexpressions again...

The question is... Do we ever perform any substitution of pre-variable to non-constant expressions?

[Jens Frenkel]

From the theoretical side yes, for example alias variables, "a=-b, pre(a) = pre(-b) = -pre(b)". To replace c=f(time) is not usefull. Maybe some information if the variable is used in pre is necesarry for the variable.

[Martin Sjölund]

The alias variables, we can easily handle in ExpressionSimplify at least

[Martin Sjölund]

I should probably open up a new bug for this optimization. I found it after adding the rule for pre(const)=const...

statement:   when false then
    k := f3("12abcdef185","eee1.txt");
  end when;
  [a.mo:19:1-21:9]
  operations: 
    simplify: pre(12) <> 12 => false
    subst: pre(i1.el.val) <> i1.el.val => pre(12) <> 12

  /*#modelicaLine [a.mo:19:1-21:9]*/
  localData->helpVars[0] = (0);
  if (edge(localData->helpVars[0])) {

Clearly, this condition can never be fulfilled, so we should not generate code for it :)

[Martin Sjölund]

Fixed in r8754