Jump prediction

Claim 2

Data processing apparatus comprising: (a) means (10) for fetching a series of instructions, including conditional jump instructions, (b) means (11, 12, 13) for executing the series of instructions, and (c) prediction means (28) for predicting the outcomes of execution of the conditional jump instructions on the basis of a stored history of previous occurrences of those instructions, characterised in that when a stored history is not available for a particular conditional jump instruction, the prediction means (28) predicts the outcome of that instruction on the basis of an internal attribute (N) of that instruction.

Claim 3

Data processing apparatus comprising (a) means for fetching a series of instructions, including conditional jump instructions, (b) means for executing the series of instructions, and (c) a memory (40) for storing a history of execution of the conditional jump instructions, characterised by (d) prediction means (39) for making a prediction of the outcome of a conditional jump instruction on the basis of an internal attribute (N) of that instruction, and (e) prediction correction means (46, 52) operable when the history of execution of a particular jump instruction is available in the memory (40), for correcting said prediction in accordance with the stored history of execution of that instruction.

Claim 4

Data processing apparatus comprising (a) means for fetching a series of instructions, including conditional jump instructions, (b) means for executing the series of instructions, and (c) a memory (40) for storing a history of execution of the conditional jump instructions, characterised by (d) prediction means (39) for making a prediction of the outcome of a conditional jump instruction on the basis of an internal attribute (N) of that instruction, and (e) prediction correction means (46, 52) operable when the history of execution of a particular jump instruction is available in the memory (40), for correcting said prediction in accordance with the stored history of execution of that instruction.

Claim 5

Apparatus according to claim 2 wherein the memory (40) holds a plurality of bits, each of which indicates whether the jump prediction for a particular jump instruction was correct on a previous occasion when said jump instruction was executed.

Claim 6

Apparatus according to claim 2 or 3 wherein said internal attribute (N) is a jump parameter.

Claim 7

Apparatus according to claim 4 wherein said prediction means (39) predicts a successful jump if said jump parameter (N) is less than a predetermined value.

Claim 8

Apparatus according to any one of claims 2-5 wherein said memory (40) is addressed by a hash address derived from the address of the jump instruction currently being processed by the prediction means.

Claim 9

Apparatus according to any one of claims 2-6 wherein said memory (40) is updated only when incorrect jump prediction is detected.

Claim 10

Apparatus according to any one of claims 2-7 wherein each location of said memory (40) holds a plurality of jump history indications, one for each of a plurality of different types of jump instruction, the apparatus also including means (47) for selecting one of the jump history indications according to the type of current jump instruction.

Claim 11

Apparatus according to any one of claims 2-8 wherein each location of said memory holds a validity field, which is set to the value of a process tag when the location is updated, the apparatus also includes means for comparing the validity field of the currently addressed location with said process tag to produce a validity signal when they match, said validity signals indicating that said stored history is available.