Intel Corporation

Bradley D Hoyt

Subramanian Natarajan

David B Papworth

Reynold V D'Sa

Glenn J Hinton

Michael A Fetterman

Ashwani Kumar Gupta

Sunil R Shenoy

Glenn I Hinton

Andrew F Glew

Rajesh Kumar

Donald D Parker

Gary L Brown

Adrian L Carbine

A Branch Target Buffer Circuit in a computer processor that predicts branch instructions with a stream of computer instructions is disclosed. The Branch Target Buffer Circuit uses a Branch Target Buffer Cache that stores branch information about previously executed branch instructions. The branch information stored in the Branch Target Buffer Cache is addressed by the last byte of each branch instruction. When an Instruction Fetch Unit in the computer processor fetches a block of instructions it sends the Branch Target Buffer Circuit an instruction pointer. Based on the instruction pointer, the Branch Target Buffer Circuit looks in the Branch Target Buffer Cache to see if any of the instructions in the block being fetched is a branch instruction. When the Branch Target Buffer Circuit finds an upcoming branch instruction in the Branch Target Buffer Cache, the Branch Target Buffer Circuit informs an Instruction Fetch Unit about the upcoming branch instruction.

Method and apparatus for implementing a set-associative branch target

A buffer is used to store information about the branch instructions within a pipelined microprocessor that can speculatively execute instructions. When a branch instruction in the microprocessor is decoded, the address of the instruction immediately following the branch instruction (the Next Linear Instruction Pointer or NLIP) and some processor state information is written into a Branch Instruction Pointer Table. The branch instruction then proceeds down the microprocessor pipeline. Eventually, the branch instruction is executed. The resolved branch outcome for the branch instruction is compared with a predicted branch outcome. If the branch prediction was correct, the microprocessor continues execution along the current path. However, if the branch prediction was wrong then the execution unit flushes the front-end microprocessor pipeline and restores the microprocessor state information that was stored in the Branch IP Table. If the branch was mispredicted as not taken, the execution unit instructs an Instruction Fetch Unit to resume execution at a final branch target address. Alternatively, if the branch was mispredicted as taken when the branch should not have been taken, the execution unit instructs the Instruction Fetch Unit to resume execution at the Next Linear Instruction Pointer (NLIP) address stored in the Branch IP Table.

Method and apparatus for a branch instruction pointer table

Method and apparatus for implementing a branch target buffer in CISC

A four stage branch instruction resolution system for a pipelined processor is disclosed. A first stage of the branch instruction resolution system predicts the existence and outcome of branch instructions within an instruction stream such that an instruction fetch unit can continually fetch instructions. A second stage decodes all the instructions fetched. If the decode stage determines that a branch instruction predicted by the first stage is not a branch instruction, the decode stage flushes the pipeline and restarts the processor at a corrected address. The decode stage verifies all branch predictions made by the branch prediction stage. Finally, the decode stage makes branch predictions for branches not predicted by the branch prediction stage. A third stage executes all the branch instructions to determine a final branch outcome and a final branch target address. The branch execution stage compares the final branch outcome and final branch target address with the predicted branch outcome and predicted branch target address to determine if the processor must flush the front-end of the microprocessor pipeline and restart at a corrected address. A final branch resolution stage retires all branch instructions. The retirement stage ensures that any instructions fetched after a mispredicted branch are not committed into permanent state.

Dual prediction branch system having two step of branch recovery process

A method and apparatus for resolving Return From Subroutine instructions in a computer processor are disclosed. The method and apparatus resolve Return From Subroutine instructions in four stages. A first stage predicts Call Subroutine instructions and Return From Subroutine instructions within the instruction stream. The first stage stores a return address in a return register when a Call Subroutine instruction is predicted. The first stage predicts a return to the return address in the return register when a Return From Subroutine instruction is predicted. A second stage decodes each Call Subroutine and Return From Subroutine instruction in order to maintain a Return Stack Buffer that stores a stack of return addresses. Each time the second stage decodes a Call Subroutine instruction, a return address is pushed onto the Return Stack Buffer. Correspondingly, each time the second stage decodes a Return From Subroutine instruction, a return address is popped off of the Return Stack Buffer. The second stage verifies predictions made by the first stage and predicts return addresses for Return From Subroutine instructions that were not predicted by the first stage. A third stage executes Return From Subroutine instructions such that the predictions are verified. Finally, a fourth stage retires Return From Subroutine instructions and ensures that no instructions fetch after a mispredicted return address are committed into permanent state.

Method and apparatus for predicting and handling resolving return from

A split queue system for a decoder that supplies one or more micro-operations and data associated with the micro-operations. A main queue is coupled to receive one or more micro-operations from the decoder, and supply it to a next processing stage to provide a process micro-operation. A shadow queue is coupled to receive data associated with the micro-operation, in the same cycle that the micro-operation is supplied to the main queue. A control circuit is coupled to the main queue for issuing micro-operation from the main queue into the next processing stage in a first cycle, and in a second cycle issuing, the micro-operation therefrom. Also in the second cycle, the control circuit issues the data associated with the micro-operation from the shadow queue, so that the data is synchronized with its associated processed micro-operation.

Decoder having a split queue system for processing intstructions in a

Method and apparatus for resolving return from subroutine instructions

A branch prediction mechanism that maintains both speculative history and actual history for each branch instruction in a branch target buffer. The actual branch history contains the branch history for fully resolved occurrences of the branch instruction. The speculative branch history contains the actual history plus the 'history' of recent branch predictions for the branch. If the speculative branch history contains any recent predictions, then a speculation bit is set. When the speculation bit is set, this indicates that there is speculative history for a branch. Therefore, when the speculation bit is set the speculative history is used to make branch predictions. If a misprediction is made for the branch, the speculation bit is cleared since the speculative history contains inaccurate branch history.

Branch target buffer for dynamically predicting branch instruction

A two level adaptive branch prediction mechanism for a computer processor. The branch prediction mechanism comprises a branch target buffer in which the branch prediction entries are partitioned into 'sets' of branch prediction entries. Each set of branch prediction entries is provided with a branch pattern table such that only the branch prediction entries in the same set share a branch pattern table thereby reducing branch pattern table interference.

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Portland, OR, United States of America

Bradley D Hoyt