Link stack repair of erroneous speculative update

Details Link stack repair of erroneous speculative update Link stack repair of erroneous speculative update

2011-06-28

2011-06-28

Chan, Eddie P (Department: 2183)

Electrical computers and digital processing systems: processing

Processing control

Branching

Reexamination Certificate

active

07971044

ABSTRACT:
Whenever a link address is written to the link stack, the prior value of the link stack entry is saved, and is restored to the link stack after a link stack push operation is speculatively executed following a mispredicted branch. This condition is detected by maintaining a count of the total number of uncommitted link stack write instructions in the pipeline, and a count of the number of uncommitted link stack write instructions ahead of each branch instruction. When a branch is evaluated and determined to have been mispredicted, the count associated with it is compared to the total count. A discrepancy indicates a link stack write instruction was speculatively issued into the pipeline after the mispredicted branch instruction, and pushed a link address onto the link stack. The prior link address is restored to the link stack from the link stack restore buffer.

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