Compilers: Principles and Practice by Pearson

302 Compilers – Principles and Practice

parallel needs a precaution: These instructions must be independent of each other in order to be able

to be executed in parallel. For example,

mov bx, ax

mov ex, bx

These instructions cannot be run in parallel, because the second instruction needs the outcome of the

first instruction, i.e. the value of BX is determined by the result of the first instruction. Look at the

next example:

mov bx, ax

mov ex, ax

This program segment can be run in parallel because now both of them only depend on AX, which

is assumed already set previously. We know that both segments mean the same thing, but the second

example is faster ...