Some Optimization Techniques

Some good optimization techniques include:

1. Generation of good code for common special cases, such as I := 0. These occur frequently enough to provide a good savings, and testing for them is fairly easy.

2. Generation of good code for subscript expressions. These often occur in loops.

3. Assigning variables to registers.
   • Much of code is loads and stores.

   • Easy case: assign a loop index variable to a register inside the loop.

   • General case: graph coloring.

4. Moving invariant code out of loops:

   
   for i := 1 to 1000 do
     x[i] := y[i] * sqrt(a);
   

   The code sqrt(a) does not change within the loop, so it could be moved above the loop and its value reused.

5. Reduction in strength: x * 8 &rarr x < < 3

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