Branch Target Buffer Run-Ahead Prediction Circuitry

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing pipeline designs face challenges in efficiently managing branch prediction, particularly in balancing accuracy and capacity, which affects performance due to increased latency in resolving branches.

Innovation Solution

The implementation of a circuitry system that includes a dedicated program counter running ahead of the normal program counter to anticipate BTB entries, allowing predicted entries to be moved to faster-access BTB levels, thereby reducing latency and improving capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If storage capacity of branch target buffer is increased to track more branches, then capacity is improved, but access latency increases

Engineering Contradiction:

Improvebranch tracking capacityVSAvoidbranch resolution latency

Core Design Contradiction:

Quantity of substanceVSLoss of time

Solution Approach 1:

The branch target buffer is divided into multiple hierarchical levels (L1, L2, L3 BTBs), each with different capacities and access speeds. The L1 BTB provides fast access for frequently used branches, while L2 and L3 provide progressively larger capacity for less frequently accessed branches, resolving the contradiction between capacity and latency through structured segmentation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A run-ahead program counter predicts future branch targets and pre-populates the L1 BTB with these predicted entries before they are actually needed. This preliminary action ensures that when branches are executed, their targets are already cached in the fast L1 BTB, reducing access latency without requiring the entire buffer to be fast.

Inventive Principle:

Principle #10Preliminary action

2Quantity of substance

If traditional single program counter approach is used, then device complexity is low, but branch prediction accuracy and capacity are limited

Engineering Contradiction:

Improvebranch prediction capacityVSAvoidprogram counter structure

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The run-ahead program counter serves multiple functions: it predicts future branch targets, pre-populates the L1 BTB, and can operate independently or in coordination with the main program counter. This multi-functionality increases branch prediction capacity without proportionally increasing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The run-ahead program counter acts as an intermediary between the main program counter and the branch target buffers. It processes branch prediction requests in advance and prepares data for the L1 BTB, mediating between the need for accurate prediction and the constraints of the main execution pipeline.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20250110882A1Branch target buffer run-ahead

Publication Date: 2025.04.03 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

Branch target buffer structures are provided. A device can include a hierarchy of branch target buffers storing entries corresponding to branch instructions, the hierarchy of branch target buffers including respective branch target buffers that have progressively slower access times. The device can include a first program counter configured to generate a first program counter value associated with a next instruction of an executing application. The device can include a second program counter configured to predict a second program counter value that is associated with a subsequent instruction of the executing application that is after the next instruction. The device can include first branch prediction circuitry configured to populate a branch target buffer of the branch target buffers based on the second program counter value.