Inefficient Code for 'or'

[Vitalij Ruge]

for the following example

  y = if f1(x) < 0 or f2(x) < 0 or f3(x) < 0 then ... else ...;

we create

  tmp1 = f1(x) < 0;
  tmp2 = f2(x) < 0;
  tmp3 = f3(x) < 0;
  y = (tmp1 || tmp2) || tmp3 ? .... : ....;

where tmp2 and tmp3 possible never used

[Martin Sjölund]

This is not an error. Modelica by design requires all of the expressions to be evaluated. If you want f2 to be evaluated only if f1(x) < 0 is false, you need to use an if-expression. Function calls can throw assertions, etc. and must be checked at run-time. So we need to evaluate tmp2 and tmp3 even if the C-code does not use the values.

[Henning Kiel]

From Modelica Spec 3.3R1 I read in chapter "3.3 Evaluation Order" that A tool is free to ... not evaluate expressions if their values do not influence the result.

So Vitalij's point seems to be correct.

[Martin Sjölund]

That would require you to analyze the side-effects of each of the above functions; we don't.

[Henning Kiel]

@sjoelund The spec states that (irrespectively of side effects!) the "tool" is free to not evaluate the expressions in short-cut logic. The tool is even allowed to reorder expressions.

[Martin Sjölund]

if their values do not influence the result

Means you can only do that if you know that it will not influence the result. See also the 3.3.1 example:

x=v[I] and (I>=1 and I<=n); // Invalid (Because the tool is not allowed to short-circuit evaluate that)