Additional simplifications for arithmetic expressions

[msoeken]

This PR adds further simplifications involving constants in arithmetic expressions, e.g., x + 0 is transformed into x; and similarly (x - 0, x * 1, x / 1, ...). It also tries to simplify expressions such that x - x becomes 0, 0 - x becomes -x, and x / x becomes 1. Works for all numeric data types.

[thomashaener]

Thanks for adding this @msoeken!
I'd suggest not to perform the rewrite x/x -> 1 though, since the resulting program would not behave as expected, e.g., for x=0 and other special cases.

[msoeken]

Thanks for adding this @msoeken!
I'd suggest not to perform the rewrite x/x -> 1 though, since the resulting program would not behave as expected, e.g., for x=0 and other special cases.

Thanks, good catch. Removed this case in the most recent commit.