Methods for partially saving a branch predictor state

A method comprising:

• maintaining, by a branch prediction unit, power to a subset of a plurality of memories, wherein each memory of the subset includes a plurality of saved branch prediction entries;
• in response to detecting an indication to exit a reduced power mode, pre-fetching, by a scheduling unit, a plurality of instructions;
• in response to determining that at least one of the plurality of instructions is a branch instruction, accessing, by the branch prediction unit, the subset of the plurality of memories;
• and
• in response to determining that a particular saved branch prediction entry of the plurality of saved branch prediction entries corresponds to the branch instruction, using, by the branch prediction unit, retained information included in the particular saved branch prediction entry to predict a direction of the branch instruction.

A system comprising:

• a scheduling unit configured to pre-fetch a plurality of instructions;
• an execution unit configured to execute the plurality of instructions;
• and
• a branch prediction unit configured to:
• store information associated with one or more executed branch instructions included in the plurality of instructions into one or more corresponding branch prediction entries in a plurality of memories;
• in response to a detection of an indication to enter a reduced power mode, power-down a first portion of the plurality of memories;
• maintain power to a second portion of memories of the plurality of memories, exclusive of the first portion;
• in response to exiting the reduced power mode, pre-fetching a group of instructions;
• in response to determining that at least one of the group of instructions is a pre-fetched branch instruction, accessing the second portion of memories;
• and
• in response to determining that a particular stored branch prediction entry of the one or more stored branch prediction entries corresponds to the pre-fetched branch instruction, using retained information included in the particular stored branch prediction entry to predict a direction of the branch instruction.