Processor Front End Parallel Decode for Branch Uncertainty

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Solution Overview

Problem

Modern processors face challenges in consistently fetching and decoding instructions to keep wide and deep pipelines of back end units busy due to imperfect branch prediction and cache misses, leading to pipeline flushes and increased power consumption.

Innovation Solution

The front end unit of processors is designed to fetch and decode two in-order sequences of instructions concurrently, one based on a control flow transfer operation, allowing for parallel processing and reducing the likelihood of pipeline flushes by predicting and preparing for reconvergent instructions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the processor waits for condition evaluation to complete before fetching and decoding instructions, then branch direction can be known with certainty, but fetching and decoding of additional instructions is unnecessarily slowed down

Engineering Contradiction:

Improvebranch direction certaintyVSAvoidinstruction fetching and decoding speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs preliminary action by fetching and decoding instructions in parallel before the condition evaluation completes. The front end unit initiates instruction fetch operations for multiple sequences simultaneously, preparing instructions ahead of time so that when condition evaluation finishes, the instructions are already ready for execution, eliminating the wait time penalty.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces a new dimension of parallelism by maintaining multiple in-order sequences of instructions simultaneously. Instead of a single linear instruction stream, the system manages multiple sequences that can be fetched and decoded in parallel, effectively adding a temporal and structural dimension to the traditional sequential execution model.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of operation

If the processor fetches and decodes instructions sequentially in a single in-order sequence, then control flow is simple to manage, but pipeline flushes occur frequently due to imperfect branch prediction and cache misses

Engineering Contradiction:

Improvecontrol flow management simplicityVSAvoidpower consumption due to pipeline flushes

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The system segments the instruction stream into multiple independent in-order sequences that can be managed separately. Each sequence maintains its own execution order and can be fetched and decoded independently, allowing the system to continue processing multiple sequences even when one sequence encounters a branch or cache miss, thereby reducing pipeline flushes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The front end unit performs preliminary fetching and decoding of instructions for multiple sequences in advance. By initiating these operations before execution is needed and maintaining them in parallel, the system prepares instructions ahead of time, reducing the impact of branch prediction failures and cache misses on overall pipeline efficiency.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If the processor maintains a single in-order sequence of instructions, then the fetch and decode process is simple, but the back end pipelines are not fully utilized due to waiting for condition evaluation

Engineering Contradiction:

Improvefetch and decode process complexityVSAvoidpipeline utilization efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The instruction stream is divided into multiple segments (in-order sequences) that can be processed in parallel. Each sequence is managed independently through its own fetch and decode process, allowing the back end pipelines to receive instructions from multiple sequences simultaneously, thereby increasing pipeline utilization efficiency without requiring complex coordination between sequences.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system transitions from a single-dimensional sequential instruction stream to a multi-dimensional parallel structure. Multiple in-order sequences are maintained and processed simultaneously, adding a temporal and structural dimension that enables the back end pipelines to be kept busy by receiving instructions from multiple sources rather than waiting for a single sequence to complete condition evaluation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS20260003622A1Processors, methods, and systems fetch and decode at least two in-order sequences of instructions in parallel

Publication Date: 2026.01.01 INTEL CORP

AI summary

A processor of an aspect includes a front end unit. The front end unit is to fetch and decode in parallel a first in-order sequence of instructions and a second in-order sequence of instructions. The first in-order sequence of instructions occurs before the second in-order sequence of instructions in program order. The processor also includes a back end unit coupled with the front end unit. The back end unit is to execute decoded instructions provided from the front end unit. Other processors, methods, systems, and instructions are disclosed.