Work Note 11, DM546, Spring 2017

Lecture March 14

Exercises March 15

• Consider possible targets for optimization other than time and space and describe plausible goals.
• Try to find patterns which could be used in a high-level peep-hole optimization of for instance C-programs. Are there any possible dangers in writing a high-level optimizer for C-programs where simple but inefficient code is replaced by more complicated but also more efficient code?
• Take a look at code generated by gcc (compile with gcc -S) for a few well-known and relatively short source files, such as factorial, for instance. Try to investigate the effect of the three options -O1, -O2, and -O3 with regards to code optimization.
• Assume that you have (structured) Intel Pentium code in a linked list of structs. Thus, entries are typically op-fields, parameter-fields, and possibly a pointer in connection with jump-instructions (therefore the term "structured"). Sketch the C-code which recognizes assembler code of the nature "x = x + 1" and replaces it by the appropriate "inc x" equivalent code.
• Find more patterns in the categories from the lecture or from new catagories that you come up with.