What are the different techniques for branch prediction?

  • 1-bit branch prediction technique.
  • 2-bit branch prediction technique.
  • Correlating branch prediction technique.

How is branch prediction implemented?

Two-way branching is usually implemented with a conditional jump instruction. A conditional jump can either be “taken” and jump to a different place in program memory, or it can be “not taken” and continue execution immediately after the conditional jump.

Where does branch prediction happen?

This is done in a special part of the processor called the branch predictor unit (BPU). The branch predictor attempts to figure out a destination of a branching instruction very early and with very little context. This magic happens before the “decoder” pipeline stage and the predictor has very limited data available.

What is an example of branch prediction?

Techopedia Explains Branch Prediction A CPU using branch prediction only executes statements if a predicate is true. One example is using conditional logic. Since unnecessary code is not executed, the processor can work much more efficiently. Branch prediction is implemented in CPU logic with a branch predictor.

Which of the following is a type of branch prediction?

Which of the following is a type of branch prediction? Explanation: There are two types of branch prediction namely static prediction and dynamic prediction.

What is the difference between static and dynamic branch prediction?

Static branch prediction makes fixed prediction of a branch to either taken or not taken; Dynamic branch prediction makes prediction based on previous history situation, by looking at history table.

How can branch prediction be improved?

One thing you can do in a high-level language is to eliminate branches by expressing the problem in terms of lookups or arithmetic. This helps branch prediction work better on the remaining branches, because there’s more “history” available.

How do you calculate branch prediction accuracy?

Will branch prediction always take only 1 cycle?

If you don’t already use tricks like MIPS I early eval of branch conditions, your branch latency would be 2 cycles (IF to EX) for conditional branches. Static always-taken prediction would shorten that to 1 cycle (IF to ID).

Why branch prediction is used?

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.

Does ARM have branch prediction?

The processor uses branch prediction to reduce the core CPI loss that arises from the longer pipeline. To improve the branch prediction accuracy, the PFU uses dynamic techniques. In ARM processors that have no PFU, the target of a branch is not known until the end of the Execute stage.

What is branch prediction logic?

Branch prediction logic: In this scheme, a prediction is made for the branch instruction currently in the pipeline. The prediction will either be taken or not taken. If the prediction is true then the pipeline will not be flushed and no clock cycles will be lost.

What is branch prediction buffer?

Branch prediction buffers contain prediction about whether the next branch will be taken (T) or not (NT), but it does not supply the target PC value. A Branch Target Buffer (BTB) does this. Instr address Predicted PC. BTB is a cache that holds. (instr addr, predicted PC)

How does a 2 bit branch predictor work?

2-bit predictor: This predictor changes prediction only on two successive mispredictions. Two bits are maintained in the prediction buffer and there are four different states. Two states corresponding to a taken state and two corresponding to not taken state.

Which of the following describes static branch prediction?

Which of the following describes static branch prediction? Hardware designer specifies to always predict a taken or untaken branch.

What is an advantage of static branch prediction?

What is an advantage of static branch prediction? Increases hardware complexity. Increased performance. Low branch prediction accuracy (no better than chance).

What are the uses of static branch predictors?

An alternative to dynamic branch predictors is the static branch predictor. These predictors may depend on the compiler to define the behavior of each conditional branch. This behavior is then adopted by the processor for the entire program execution.

What is branchless programming?

Branchless programming is a programming technique that eliminates the branches (if, switch, and other conditional statements) from the program. Although this is not much relevant these days with extremely powerful systems and usage of interpreted languages( especially dynamic typed ones).

What is bimodal branch prediction?

The most well known technique, referred to here as bimodal branch prediction, makes a prediction based on the direction the branch went the last few times it was executed. More recent work has shown that significantly more accurate predictions can be made by utilizing more branch history.

How many clock cycles are wasted by a branch Misprediction?

— Mispredicting a branch means that two clock cycles are wasted.

What decides the index of the prediction bit in the branch prediction table?

Indexing is done by concatenating the global history bits and the number of required bits from the branch address. For example, the predictor shown below uses a 2-bit global history to choose from among four predictors for each branch address. Each of these predictors is a 2-bit predictor for that branch.

What is branching in pipelining?

Pipelining is a very effective method for speeding up instruction execution along a sequential path. But if a branch introduces the pipeline and disorganizes the sequential processing, the implementation of the pipeline will be seriously disrupted unless appropriate methods are used.

What is meaning of delayed branch and branch prediction write a difference between them?

Delayed branch simply means that some number of instructions that appear after the branch in the instruction stream will be executed regardless of which way the branch ultimately goes.

Are branches slow?

A branch instruction is not inherently slower than any other instruction. However, the reason you heard that branches should avoided is because modern CPUs follow a pipeline architecture. This means that there are multiple sequential instructions being executed simultaneously.

How does Intel branch prediction work?

It predicts where to fetch from next cycle, and then based on that prediction it predicts where to fetch from the cycle after that, and so on. It doesn’t use any information about the decoded instructions, but only past behavior of the branches.

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