SPIR Overview

The Industry Open Standard Intermediate Language for Parallel Compute and Graphics

SPIR-V is catalyzing a revolution in the ecosystem for shader and kernel language compilers used for expressing parallel computation and GPU-based graphics. SPIR-V enables high-level language front-ends to emit programs in a standardized intermediate form to be ingested by Vulkan, OpenGL or OpenCL drivers. SPIR-V eliminates the need for high-level language front-end compilers in device drivers, significantly reducing driver complexity, enables a broad range of language and framework front-ends to run on diverse hardware architectures and encourages a vibrant ecosystem of open source analysis, porting, debug and optimization tools.

For developers, using SPIR-V means that kernel source code no longer has to be directly exposed, kernel load times can be accelerated, and developers can choose the use of a common language front-end compiler, improving kernel reliability and portability across multiple hardware implementations.

SPIR-V Language Ecosystem

The SPIR-V ecosystem includes a rich variety of language front-ends, tools and run-times

SPIR-V Specifications

• The SPIR V 1.5 Specification is available in the Khronos Registry
• SPIR-V 1.5 in the Vulkan 1.2 Press Release
• SPIR-V Tools project including an assembler, binary module parser, disassembler, optimizer, linker, and validator for SPIR-V

SPIR–V 1.3 Resources

• The SPIR V 1.3 Specification is available in the Khronos Registry
• SPIR-V 1.3 in the Vulkan 1.1 Press Release
• SPIR-V Tools project including an assembler, binary module parser, disassembler, optimizer, linker, and validator for SPIR-V
• SPIR-V Cross is a practical tool and library for performing reflection on SPIR-V and disassembling SPIR-V back to high level languages.
• SPIR-V LLVM Translator contains a LLVM <-> SPIR-V converter intended to serve as a foundation for LLVM-based front-end compilers targeting SPIR-V.
• SPIR-V issue reporting on GitHub
• SPIR-V feedback forum offers community support for questions and feedback

SPIR–V 1.2 Resources

• The SPIR V 1.2 Specification is available in the Khronos Registry

SPIR–V 1.1 Resources

• The SPIR V 1.1 Specification is available in the Khronos Registry

SPIR–V 1.0 Resources

• The SPIR V 1.0 Specification is available in the Khronos Registry
• SPIR-V Whitepaper An Introduction to SPIR-V

About SPIR and SPIR-V

SPIR (Standard Portable Intermediate Representation) was initially developed for use by OpenCL and SPIR versions 1.2 and 2.0 were based on LLVM. SPIR has now evolved into a cross-API intermediate language that is fully defined by Khronos with native support for shader and kernel features used by APIs such as Vulkan – called SPIR-V.

	SPIR 1.2	SPIR 2.0	SPIR-V 1.X
LLVM Interaction	Uses LLVM 3.2	Uses LLVM 3.4	100% Khronos defined Round-trip lossless conversion
Compute Constructs	Metadata/Intrinsics	Metadata/Intrinsics	Native
Graphics Constructs	No	No	Native
Supported Language Feature Supported	OpenCL C 1.2	OpenCL C 1.2 OpenCL C 2.0	OpenCL C 1.2 / 2.X OpenCL C++ GLSL
OpenCL Ingestion	OpenCL 1.2 Extension	OpenCL 2.0 Extension	OpenCL 2.1/2.2 Core
Graphics API Ingestion	—	—	Vulkan 1.X and OpenGL 4.6 Core

SPIR-V is the first open standard, cross-API intermediate language for natively representing parallel compute and graphics and is part of the core specifications of OpenCL 2.1, OpenCL 2.2, and the Vulkan GPU API. SPIR-V is also supported in an OpenGL 4.6 extension. SPIR–V does not use LLVM, and so is isolated from LLVM roadmap changes. Khronos has open sourced SPIR-V/LLVM conversion tools to enable construction of flexible toolchains that use both intermediate languages.

SPIR-V exposes the machine model for OpenCL 1.2, 2.0, 2.1, 2.2 and Vulkan - including full flow control, and graphics and parallel constructs not supported in LLVM. SPIR-V also supports OpenCL C and OpenCL C++ kernel languages as well as the GLSL shader language for Vulkan and OpenGL.

SPIR-V 1.1, launched in parallel with OpenCL 2.1, supported the kernel language features of OpenCL C++ in OpenCL 2.1, including initializer and finalizer function execution modes to support constructors and destructors. SPIR-V 1.1 also enhances the expressiveness of kernel programs by supporting named barriers, subgroup execution, and program scope pipes.

SPIR-V 1.2 launched in parallel with OpenCL 2.2 and fully supports the final OpenCL C++ kernel language and adds support for runtime specialization of key tuning parameters in OpenCL 2.2 such as workgroup size.

SPIR-V 1.3, launched in parallel with Vulkan 1.1, expands the capabilities of the Vulkan shader intermediate representation to support subgroup operations and enables enhanced compiler optimizations.

SPIR 1.2/2.0 Resources

SPIR 2.0 is a mapping from the OpenCL C programming language into LLVM IR. This version of the SPIR is based on LLVM 3.2 and OpenCL C as defined in the OpenCL 2.0 specification. SPIR 2.0 supports all core features and KHR extensions for version 2.0 of OpenCL C

• It’s recommend that all SPIR uses migrate, when possible, to SPIR-V
• The SPIR 2.0 Provisional Specification is available in the Khronos Registry
• The SPIR 1.2 Specification is available in the Khronos Registry
• The SPIR 1.2 Verifier from Khronos GitHub