Itanium® Architecture for Programmers: Understanding 64-Bit Processors and EPIC Principles

5.1. Hardware Basis for Control of Flow

Control of logical flow based upon currently calculated conditions gives computer programs their extraordinary power and versatility. Procedure calls and subroutine calls can be important forms of control when they facilitate organizing a program into coherent modules, but are perhaps not as essential, or as fundamental, as branch instructions. A running computer program makes “decisions” by comparing a current result against a fixed standard or computed quantity using some logical relationship, such as equality or greater-than. The machine must have some type of instruction that can bring about a different course of program flow for two opposite outcomes of an implicit test, such as less-than-or-equal-to ...