Dynamic Two-Pass Execution for Partial Flag Updating

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Solution Overview

Problem

In processors, partial flag updating instructions face challenges in handling flag registers, leading to unnecessary delays due to false dependencies and resource inefficiencies, particularly when flag registers are renamed and split into multiple logical registers, which increases overhead and power consumption.

Innovation Solution

Implementing dynamic two-pass execution for partial flag register updating instructions, allowing the instruction to remain as a single micro-operation throughout the pipeline and optimizing execution based on dynamic execution status, without splitting into multiple micro-operations or injecting synchronization micro-operations, thus minimizing resource usage and overhead.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If flag registers are renamed and split into multiple logical registers, then false dependencies are handled, but overhead and power consumption increase

Engineering Contradiction:

Improvefalse dependency handlingVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The system dynamically determines whether to use single-pass or two-pass execution for partial flag updating instructions based on runtime conditions. The execution unit selects the appropriate execution mode dynamically, avoiding the static overhead of always using two-pass execution while still handling false dependencies when necessary.

Inventive Principle:

Principle #15Dynamics

2Productivity

If partial flag updating instructions are executed using single-pass execution, then resource usage is minimized, but false dependencies cause delays

Engineering Contradiction:

Improveresource usage efficiencyVSAvoidexecution delay

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The execution unit dynamically switches between single-pass and two-pass execution modes based on the specific instruction and runtime conditions. For instructions without false dependency issues, single-pass execution maintains high efficiency. For instructions with false dependencies, two-pass execution eliminates the delays, optimizing overall performance adaptively.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the execution parameter (number of passes) based on the instruction type and dependency analysis. Partial flag updating instructions that exhibit false dependencies are executed in two passes, while others use single-pass execution, allowing flexible parameter adjustment to resolve contradictions between speed and correctness.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If two-pass execution is always used for partial flag updating instructions, then false dependencies are eliminated, but resource queuing and pipeline bandwidth overhead increase

Engineering Contradiction:

Improvefalse dependency eliminationVSAvoidpipeline overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The execution unit implements dynamic selection between single-pass and two-pass execution modes. The control logic analyzes each partial flag updating instruction and selects the appropriate execution mode, avoiding the unnecessary complexity and overhead of always using two-pass execution while still eliminating false dependencies when required.

Inventive Principle:

Principle #15Dynamics

4Reliability

If partial flag updating instructions are split into multiple micro-operations, then flag register updates are handled correctly, but instruction overhead increases

Engineering Contradiction:

Improveflag register update correctnessVSAvoidinstruction overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system dynamically determines whether to use single-pass or two-pass execution for partial flag updating instructions. This dynamic approach allows the instruction to remain as a single micro-operation in most cases, avoiding the overhead of splitting, while still correctly handling flag register updates when executed in two passes when false dependencies are detected.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12039329B2Methods, systems, and apparatuses to optimize partial flag updating instructions via dynamic two-pass execution in a processor

Publication Date: 2024.07.16 INTEL CORP

AI summary

Systems, methods, and apparatuses relating to circuitry to implement dynamic two-pass execution of a partial flag updating instruction in a processor are described. In one embodiment, a hardware processor core includes a decoder circuit to decode instructions into a set of one or more micro-operations, an execution circuit to execute the micro-operations decoded for the instructions, a data register to store data, a flag register to store a plurality of flags, and a reservation station circuit coupled between the decoder circuit and the execution circuit, the reservation station circuit to, in response to an indicator bit set to a multiple pass mode for a single micro-operation in a reservation station entry, perform a first dispatch of the single micro-operation to the execution circuit, when a source data operand in the data register is ready for execution and a source flag operand in the flag register is not ready for execution, to generate a data resultant, and a second dispatch of the single micro-operation to the execution circuit when both the source data operand in the data register and the source flag operand in the flag register are ready for execution to generate a flag resultant based on one or more of the plurality of flags in the flag register.