Processor architecture supporting multiple speculative branching

A data processing system that performs operations responsive to a program including a plurality of instructions, the instructions including at least a first and second test instruction and at least a first and second branch instruction that determine an intended sequence of execution of the instructions within the program responsive to results of the first and second test instructions respectively, the system comprising:

• an operation unit that executes the instructions by performing operations responsive to the instructions;
• a branch prediction unit that speculates a first intended sequence of execution of the instructions responsive to the first branch instruction and speculates a second intended sequence of execution of the instructions responsive to the second branch instruction, the first and second intended sequences affecting sequence of execution of instructions by the operation unit;
• an evaluation unit that determines, responsive to execution of the first test instruction by the operation unit, whether the branch prediction unit has speculated the first intended sequence correctly, wherein the branch prediction unit speculates the second intended sequence prior to execution of the first test instruction;
• a repair unit that, upon a determination by the evaluation unit that the branch unit has speculated either the first intended sequence or the second intended sequence incorrectly, nullifies the effects of instructions of the incorrectly speculated intended sequence;
• and
• a result storage unit that stores results of the operations performed responsive to the instructions, and wherein the repair unit nullifies an instruction by reversing any update of results to the result storage unit affected by the nullified instruction and preventing any further update of results to the result storage unit by any future performance of operations responsive to the nullified instruction.

A data processing system capable of executing a sequence of instructions, the sequence including a plurality of branch instructions, each branch instruction of the plurality associated with a test instruction, the data processing system comprising:

• means for predicting speculative sequences of instructions following each branch instruction within the sequence of instructions;
• means for fetching the speculative sequences of instructions from an instruction memory;
• means for performing operations responsive to instructions in the instruction sequence, including the speculative sequences;
• means for shelving the plurality of branch instructions;
• means for evaluating each branch instruction stored in the shelving means subsequent to performance of an operation responsive to the test instruction associated with the branch instruction to determine based on a result of the operation performed responsive to the test instruction whether the branch instruction associated with the test instruction was correctly predicted;
• and
• means, upon detection of an incorrectly predicted branch instruction by the evaluating means, for repairing the incorrectly predicted branch instruction and instructions of the speculative sequence following the branch instruction predicted by the predicting means;
• wherein the predicting means is capable of predicting a speculative sequence of instructions following a later branch instruction while an earlier branch instruction remains unevaluated and the repairing means is capable of repairing the either the later branch instruction of the earlier branch instruction if they are determined to be incorrectly predicted.