Draw a concise AST for the following tiger expression, label each node
with the "result register" attribute for the Sethi-Ullman register
allocation algorithm, and show the resulting code. Spend up to 20
minutes working on this (hopefully this will give everyone a chance to
complete the register allocation part and at least start to think
about the function call part).

    printint( (20+20) + (1+2; 2) )

Note that "printint" is from my extended version of the tiger standard
library. This procedure takes one integer and doesn't return anything.
The extended tiger library is described in the comment at the start of
the file /home/courses/lib/Hassem/Tiger-stdlib-stack.hera on the lab
machines.