International Business Machines Corporation

Gururaj S Rao

Howard E Sachar

Philip George Emma

Balakrishna Raghavendra Iyer

Satya Prakash Sharma

Inderpal Singh Narang

Casper A Scalzi

Rudolph N Rechtschaffen

Richard I Baum

James H Pomerene

Glen A Brent

Frank J Sparacio

Bhaskar Sinha

Jacques J Losq

Hatem M Ghafir

Lee H Wilson

A data-dependent branch table is a mechanism that is sensitive to operands that will be tested in order to determine branch action outcomes. The data dependent branch table operates in conjunction with a branch history table to anticipate those instances where the branch history table will make an erroneous prediction, and corrects the branch history table prior to the time that the actual prediction is made.

Branch prediction mechanism in which a branch history table is updated

A method and apparatus predicting the outcome of a conditional branch instruction based on the previous performance of the branch, rather than on the instruction fields. The prediction of the outcome of a conditional branch instruction is performed utilizing a table that records the history of the outcome of the branch at a given memory location. A decode-time history table (DHT) is utilized. The DHT attempts to guess only the outcome of a conditional branch instruction, but not its target address. Thus, it can only be used to guess the branch outcomes at decode time when the target address is available. During the decoding of a conditional branch instruction, a table is accessed using the memory address of the branch instruction itself or some portions thereof. The table records the history of the outcomes of the branch at this memory location up to the congruence of the table size. A combinational circuit determines the guess (taken or not taken) from the branch history as provided by the table.

Decode history table for conditional branch instructions

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Gururaj S Rao