Advanced Micro Devices Corporation

Aparna Thyagarajan

Marius Evers

Ashok Tirupathy Venkatachar

Arunachalam Annamalai

Anthony Jarvis

William Evan Jones, Iii

Angelo Wong

Techniques for controlling prefetching of instructions into an instruction cache are provided. The techniques include tracking either or both of branch target buffer misses and instruction cache misses, modifying a throttle toggle based on the tracking, and adjusting prefetch activity based on the throttle toggle.

Instruction cache prefetch throttle

A set of entries in a branch prediction structure for a set of second blocks are accessed based on a first address of a first block. The set of second blocks correspond to outcomes of one or more first branch instructions in the first block. Speculative prediction of outcomes of second branch instructions in the second blocks is initiated based on the entries in the branch prediction structure. State associated with the speculative prediction is selectively flushed based on types of the branch instructions. In some cases, the branch predictor can be accessed using an address of a previous block or a current block. State associated with the speculative prediction is selectively flushed from the ahead branch prediction, and prediction of outcomes of branch instructions in one of the second blocks is selectively initiated using non-ahead accessing, based on the types of the one or more branch instructions.

Selectively performing ahead branch prediction based on types of branch instructions

A processor predicts a number of loop iterations associated with a set of loop instructions. In response to the predicted number of loop iterations exceeding a first loop iteration threshold, the set of loop instructions are executed in a loop mode that includes placing at least one component of an instruction pipeline of the processor in a low-power mode or state and executing the set of loop instructions from a loop buffer. In response to the predicted number of loop iterations being less than or equal to a second loop iteration threshold, the set of instructions are executed in a non-loop mode that includes maintaining at least one component of the instruction pipeline in a powered up state and executing the set of loop instructions from an instruction fetch unit of the instruction pipeline.

Using loop exit prediction to accelerate or suppress loop mode of a processor

A processor includes a branch target buffer (BTB) having a plurality of entries whereby each entry corresponds to an associated instruction pointer value that is predicted to be a branch instruction. Each BTB entry stores a predicted branch target address for the branch instruction, and further stores information indicating whether the next branch in the block of instructions associated with the predicted branch target address is predicted to be a return instruction. In response to the BTB indicating that the next branch is predicted to be a return instruction, the processor initiates an access to a return stack that stores the return address for the predicted return instruction. By initiating access to the return stack responsive to the return prediction stored at the BTB, the processor reduces the delay in identifying the return address, thereby improving processing efficiency.

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Santa Clara, CA, United States of America

Aparna Thyagarajan