Following code generation there are further optimizations that are possible. The code is scanned a few instructions at a time (the peephole) looking for combinations of instructions that may be replaced by more efficient combinations. Typical optimizations performed by a peephole optimizer include copy propagation across register loads and stores, strength reduction in arithmetic operators and memory access, and branch chaining.

We do not illustrate a peephole optimizer for Simp.

x := x + 1         ld x       ld x

                   inc        inc

                   store x    dup

y := x + 3         ld x   

                   ld 3       ld 3

                   add        add

                   store y    store y

x := x + z         ld x

                   ld z       ld z

                   add        add

                   store x    store x