Why out of order processor use a technique called register renaming

Out-of-order processors use a technique called register renaming to eliminate WAR and WAW hazards. Register renaming adds some nonarchitectural renaming registers to the processor. For example, a processor might add 20 renaming registers, called T0–T19.

1. What is register renaming and explain its purpose?
2. What is out of order processor?
3. How does out of order execution work?
4. What do we mean when we say out order issue with out order completion?
5. What is register renaming and why is it used in superscalar processors?
6. How the register renaming is implemented in Tomasulo's approach?
7. Which of the following is a type of out of order execution?
8. Which architecture supports out of order execution?
9. Which processor uses in-order execution?
10. What is the different between in-order and out order superscalar processor?
11. When the processor tries to execute an instruction that was not fetched is called?
12. What type of data hazard becomes possible with out of order completion of instructions?
13. Why is in-order commit mandatory for a speculative out of order processor?
14. What is called when the processor executes multiple instructions at a time?
15. What is VLIW processor?

What is register renaming and explain its purpose?

Register renaming is a form of pipelining that deals with data dependences between instructions by renaming their register operands. ... Renaming replaces architectural register names by, in effect, value names, with a new value name for each instruction destination operand.

What is out of order processor?

Out-of-order processors

The instruction waits in the queue until its input operands are available. The instruction can leave the queue before older instructions. The instruction is issued to the appropriate functional unit and executed by that unit. The results are queued.

How does out of order execution work?

With out-of-order execution (OoO for short), the processor would issue each of the instructions in program order, and then enter a new pipeline stage called "read operands" during which instructions whose operands are available would move to the execution stage, regardless of their order in the program.

What do we mean when we say out order issue with out order completion?

Out-of-order issue, out-of-order completion. With in-order issue, the processor will only decode instructions up to the point of. dependency or conflict. The processor cannot look ahead of the point of conflict to subsequent instructions that may.

What is register renaming and why is it used in superscalar processors?

Abstract: Register renaming is a technique to remove false data dependencie-write after read (WAR) and write after write (WAW)-that occur in straight line code between register operands of subsequent instructions.

How the register renaming is implemented in Tomasulo's approach?

Tomasulo's algorithm implements register renaming through the use of what are called reservation stations. Reservation stations are buffers which fetch and store instruction operands as soon as they're available. Source operands point to either the register file or to other reservation stations.

Which of the following is a type of out of order execution?

Software pipelining is a type of out-of-order execution, except that the reordering is done by a compiler instead of the processor.

Which architecture supports out of order execution?

Which of the following architecture supports out-of-order execution? Explanation: Superscalar architecture support out-of-order execution in which the instructions later in the stream are executed before earlier instructions.

Which processor uses in-order execution?

In out-of-order processor, the instructions are executed in an order of availability of operands The steps required for In-order processor are as follows: 1. The processor retrieves program instructions from its memory.

What is the different between in-order and out order superscalar processor?

More precisely, superscalar processors can start executing two or more instructions in the same cycle. Pipelined processors can execute more than one instruction at a time, but a non-superscalar pipelined processor will only start a single instruction in any given cycle.

When the processor tries to execute an instruction that was not fetched is called?

Undefined instruction occurs when an unknown instruction is fetched. This exception is caused by an instruction in the IR that has an unknown opcode or an R-type instruction that has an unknown function code. System call occurs when the processor executes a syscall instruction.

What type of data hazard becomes possible with out of order completion of instructions?

WAR and WAW hazards occur during the out-of-order execution of the instructions.

Why is in-order commit mandatory for a speculative out of order processor?

It happens even on in-order pipelined CPUs. In-order commit is necessary¹ for precise exceptions that can roll-back to exactly the instruction that faulted, without any instructions after that having already retired. The cardinal rule of out-of-order execution is don't break single-threaded code.

What is called when the processor executes multiple instructions at a time?

In contrast to a scalar processor that can execute at most one single instruction per clock cycle, a superscalar processor can execute more than one instruction during a clock cycle by simultaneously dispatching multiple instructions to different execution units on the processor.

What is VLIW processor?

Very long instruction word (VLIW) describes a computer processing architecture in which a language compiler or pre-processor breaks program instruction down into basic operations that can be performed by the processor in parallel (that is, at the same time).