Weekly Note 7, DM18, Spring 2007

Lecture February 27

• Code generation.

Exercises March 9

• Consider code generation templates for the following constructions:
  • for-loops (Pascal style): for i:=7 to 42 do SOMETHING.
  • for-loops (C style).
  • loops with break/continue, i.e., the loop is as a starting point infinte, break exits the loop and continue starts from the beginning. For both break and continue, this is independent of where in the loop code you are.
  • switch (C) and case (Pascal) constructions.
  • records.
  • arrays.
  • multi-dimensionel arrays; this is different from arrays of arrays. You must find a layout such that you can efficiently compute the address of A[i,j,k], for instance. Thus, it must be different from following three pointers as you would logically do if you used A[i][j][k].
  • conditional expressions in C style: ( exp ? exp : exp ).
• What is the semantics of i:= 7; for i:=i+1 to i+2 do {i:=i+3; print i} according to your template above, i.e., what is printed? What are the reasonable behaviors?
• Are there efficiency reasons to restrict switch/case expressions to be simple types and only use values from a small domain?
• Some programming languages offer lists with random access (A[i]), append (A.append(42)), and insert (A.insert(pos,val)) which inserts val in between the positions pos and pos+1. Can this be implemented efficiently?
• Consider constructions which are typically allocated in the heap, e.g., Tigris arrays or C structs. How can they give rise to (enormous) vaste of space? How is it possible in principle to check if allocated space is still used and thereby "collect" unused space for reuse?