CPU - Branch

About

• forward branches (used to implement conditional operations like if statements)
• backward branches (used to implement loops).

Branches may be:

• unconditional (always taken),
• or conditional (taken or not, depending on a computed value).

To avoid a stall, the processor must guess which instruction to fetch next:

• the next one in memory order (corresponding to an untaken branch),
• or the one at the branch target (corresponding to a taken branch).

Articles Related

Prediction

A branch predictor helps the processor make an intelligent guess about whether a branch will be taken or not. It does this by gathering statistics about how often particular branches have been taken in the past.

The performance of an if-statement depends on whether its condition has a predictable pattern. branch prediction fail

Documentation / Reference

• https://www.raspberrypi.org/blog/why-raspberry-pi-isnt-vulnerable-to-spectre-or-meltdown/