How does a branch prediction work?

Branch prediction attempts to guess whether a conditional jump will be taken or not. Branch target prediction attempts to guess the target of a taken conditional or unconditional jump before it is computed by decoding and executing the instruction itself.

What is branch prediction explain various schemes?

Basically branch prediction predicts two problems: 1) direction predicting, and 2) calculating the target address. Branch prediction schemes are of two types: static branch schemes and dynamic branch schemes. A static branch scheme (software techniques) is very simple and easy.

What is branch prediction data flow analysis and speculative execution?

Speculative execution uses branch prediction to guess which instructions will most likely be needed in the near future and data flow analysis to arrange the instructions for optimal execution (instead of executing them in the order they came in).

What is branch prediction in CPU?

Branch prediction is a technique used in CPU design that attempts to guess the outcome of a conditional operation and prepare for the most likely result. A digital circuit that performs this operation is known as a branch predictor. It is an important component of modern CPU architectures, such as the x86.

At what point does a branch predictor predict branches?

The branch predictor operates in the Fetch stage of the pipeline so that it can determine which instruction to execute on the next cycle. When it predicts that the branch should be taken, the processor fetches the next instruction from the branch destination stored in the branch target buffer.

What is branch prediction and speculative execution?

Branch prediction is done by the processor to try to determine where the execution will continue after a conditional jump, so that it can read the next instruction(s) from memory. Speculative execution goes one step further and determines what the result would be from executing the next instruction(s).

What is meant by branch prediction speculative execution and pipelining?

When is a decision made in dynamic branch prediction?

In static prediction, all decisions are made at compile time, before the execution of the program. Dynamic branch prediction uses information about taken or not taken branches gathered at run-time to predict the outcome of a branch.

Is there a processor that can predict branch direction?

Some superscalar processors (MIPS R8000, Alpha 21264, and Alpha 21464 (EV8)) fetch each line of instructions with a pointer to the next line. This next-line predictor handles branch target prediction as well as branch direction prediction.

What’s the difference between branch prediction and target prediction?

Branch prediction attempts to guess whether a conditional jump will be taken or not. Branch target prediction attempts to guess the target of a taken conditional or unconditional jump before it is computed by decoding and executing the instruction itself.

How many instructions are wasted in a branch predictor?

When a next-line predictor points to aligned groups of 2, 4, or 8 instructions, the branch target will usually not be the first instruction fetched, and so the initial instructions fetched are wasted. Assuming for simplicity, a uniform distribution of branch targets, 0.5, 1.5, and 3.5 instructions fetched are discarded, respectively.