Name Strings

SPV_KHR_terminate_invocation

Contact

To report problems with this extension, please open a new issue at:

https://github.com/KhronosGroup/SPIRV-Headers

Contributors

  • Alan Baker, Google LLC

  • Jeff Bolz, NVIDIA

  • John Kessenich, Google LLC

  • David Neto, Google LLC

  • Kevin Petit, ARM

Notice

Copyright (c) 2020 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html

Status

  • Complete

  • Approved by the SPIR Working Group: 2020-05-13

  • Approved by the Khrono Board of Promoters: 2020-06-26

Version

Last Modified Date

2020-05-01

Revision

2

Dependencies

This extension is written against the SPIR-V Specification, Version 1.5 Revision 2.

This extension requires SPIR-V 1.0.

Overview

This extension adds a new instruction OpTerminateInvocation to provide a disambiguated functionality compared to OpKill.

Extension Name

To use this extension within a SPIR-V module, the following OpExtension must be present in the module:

OpExtension "SPV_KHR_terminate_invocation"

Modifications to the SPIR-V Specification, Version 1.5

Terms

In section 2.2.5 "Control Flow", add OpTerminateInvocation to the Termination Instruction list.

Instructions

In section 3.22.17 "Control-Flow Instructions", add the new instruction:

OpTerminateInvocation

Fragment-shader terminate.

Ceases all further processing in any invocation that executes it: Only instructions these invocations executed before OpTerminateInvocation will have observable side effects. If this instruction is executed in non-uniform control flow, all subsequent control flow is non-uniform (for invocations that continue to execute).

This instruction must be the last instruction in a block.

This instruction is only valid in the Fragment Execution Model.

Capability:
Shader

1

4416

Issues

1) Why not just continue to use OpKill?

Discussion:

Historically, OpKill was mapped for both GLSL and HLSL discard builtins; however, the behavior of the two operations differs. HLSL’s discard maps more naturally to OpDemoteToHelperInvocationEXT (see SPV_EXT_demote_to_helper_invocation). Implementors naturally implemented OpKill to match their hardware, which might use either semantics. Introducing OpTerminateInvocation allows for better disambiguation of the desired behavior by an application and more rigorous testing of effects.

Revision History

Rev Date Author Changes

1

2020-04-08

Alan Baker

Initial revision

1

2020-05-01

Alan Baker

Rename extension