Stmicroelectronics (beijing) R&d Company Ltd.

Stmicroelectronics R&d (beijing) Co. Ltd

Kai-Feng Wang

Hong-Xia Sun

Yong-Qiang Wu

Peng-fei Zhu

Hong- Xia Sun

Peng-Fei Zhu

A system and method for predicting the execution of a branch of computer-executable instructions. In an embodiment, a branch predictor may include a program-counter register operable to store a program-counter value and a branch-history register operable to store a branch-history value. Additionally, the branch predictor may include a prediction hash table having a plurality of prediction values each uniquely corresponding to a plurality of memory locations. With these components, the branch predictor may generate a first prediction value that corresponds to the program-counter value and may generate a second prediction value that corresponds to a logical combination of the program-counter value and the branch-history value. With these two prediction values obtained from two different prediction schemas, the branch predictor is better suited to generate an overall prediction value based on the first and second prediction values that is more accurate than a single prediction value based upon a single prediction schema.

System and method for a multi-schema branch predictor

Some microprocessors check branch prediction information in a branch history table and/or a branch target buffer. To check for branch prediction information, a microprocessor can identify which instructions are control flow instructions and which instructions are non control flow instructions. To reduce power consumption in the branch history table and/or branch target buffer, the branch history table and/or branch target buffer can check for branch prediction information corresponding to the control flow instructions and not the non control flow instructions.

Reducing branch checking for non control flow instructions

A technique for selecting instructions for execution from an issue queue at multiple function units while reducing the chances of instruction collisions. In an embodiment, each function unit in a processor may include a selection logic circuit that selects a specific instruction from the issue queue for execution. In order to avoid instruction collision, a function unit may have a selection logic circuit that may select two instructions from an instruction queue: one according to a first selection technique and one according to a second selection technique. Then, by comparing the instruction selected by the first selection technique to the instruction selected by the selection logic circuit of another function unit, the instruction selected by the second technique may be used instead if there will be an instruction collision because the instruction selected by the first selection technique is the same as the instruction selected at a different function unit.

Reducing instruction collisions in a processor

A system for recovering an architecture register mapping table (ARMT). The system includes a first number of collection circuits and decode circuits, a second number of selection circuits, and an enable circuit. Information related to the mapping between each physical register and an appropriate architecture register is obtained from a physical register mapping table (PRMT) by one and only one collection circuit during only one of a fourth number of instruction cycles. Each decode circuit has its input coupled to the output of one different collection circuit and is capable of converting its input into a third number bit wide binary string selection code at its output. Each selection circuit is configured to receive from each selection code a bit from a bit position associated with that selection circuit. The enable circuit is configured to appropriately enable mapping of information from the PRMT to the ARMT.

Power efficient system for recovering an architecture register mapping table

A comparison circuit can reduce the amount of power consumed when searching a load queue or a store queue of a microprocessor. Some embodiments of the comparison circuit use a comparison unit that performs an initial comparison of addresses using a subset of the address bits. If the initial comparison results in a match, a second comparison unit can be enabled to compare another subset of the address bits.

Reduced power load/store queue searching by comparing subsets of address bits and enabling second subset comparison based on first subset comparison result

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Beijing, China

Kai-Feng Wang