Standard Portable Intermediate Representation (SPIR) is an

intermediate language An intermediate representation (IR) is the data structure or code used internally by a compiler or virtual machine to represent source code. An IR is designed to be conducive to further processing, such as optimization and translation. A "good" ...

for

parallel computing Parallel computing is a type of computing, computation in which many calculations or Process (computing), processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. ...

and graphics by

Khronos Group The Khronos Group, Inc. is an open, non-profit, member-driven consortium of 170 organizations developing, publishing and maintaining royalty-free interoperability standards for 3D graphics, virtual reality, augmented reality, parallel computat ...

. It is used in multiple execution environments, including the

Vulkan Vulkan is a cross-platform API and open standard for 3D graphics and computing. It was intended to address the shortcomings of OpenGL, and allow developers more control over the GPU. It is designed to support a wide variety of GPUs, CPUs and o ...

graphics API A graphics library or graphics API is a program library designed to aid in rendering computer graphics to a monitor. This typically involves providing optimized versions of functions that handle common rendering tasks. This can be done purely in ...

and the

OpenCL OpenCL (Open Computing Language) is a software framework, framework for writing programs that execute across heterogeneous computing, heterogeneous platforms consisting of central processing units (CPUs), graphics processing units (GPUs), di ...

compute API, to represent a

shader In computer graphics, a shader is a computer program that calculates the appropriate levels of light, darkness, and color during the rendering of a 3D scene—a process known as '' shading''. Shaders have evolved to perform a variety of s ...

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

. It is also used as an interchange language for cross compilation. SPIR-V is a new version of SPIR which was introduced in 2015 by the

, and has since replaced the original SPIR, which was introduced in 2012. On September 19th 2024, Microsoft has announced plans to adopt SPIR-V as the

Direct3D Direct3D is a graphics application programming interface (API) for Microsoft Windows. Part of DirectX, Direct3D is used to render three-dimensional graphics in applications where performance is important, such as games. Direct3D uses hardware ...

Interchange format in place of DXIL, beginning support from Shader Model 7 on.

Purpose

The purposes of SPIR-V are to natively represent the primitives needed by compute and graphics; to separate high-level language from the interface to compute and graphics drivers; to be the distribution form, or distribute fully compiled binaries; to be a fully self-contained specification; and to support multiple APIs. It is also used as an intermediate target for cross-compilation tools. For example, SPIR-V allows the Vulkan API to use any

shading language A shading language is a graphics programming language adapted to programming shader effects. Shading languages usually consist of special data types like "vector", "matrix", "color" and " normal". Offline rendering Shading languages used in of ...

, including

GLSL OpenGL Shading Language (GLSL) is a high-level shading language with a syntax based on the C programming language. It was created by the OpenGL ARB (OpenGL Architecture Review Board) to give developers more direct control of the graphics pipe ...

and

HLSL The High-Level Shader Language or High-Level Shading Language (HLSL) is a proprietary shading language developed by Microsoft for the Direct3D 9 API to augment the shader assembly language, and went on to become the required shading language ...

. SPIR-V can be decompiled into several shading languages (

, GLSL ES, MSL,

) using SPIRV-Cross, so that these languages can be interconverted. It also has paths to and/or from

WebGPU WebGPU API is a JavaScript, Rust, C++, and C API for cross-platform efficient graphics processing unit (GPU) access. Using a system's underlying Vulkan, Metal, or Direct3D 12 technologies, WebGPU allows for graphics processing, games, and mor ...

SYCL SYCL (pronounced "sickle") is a higher-level programming model to improve programming productivity on various hardware accelerators. It is a single-source embedded domain-specific language ( eDSL) based on pure C++17. It is a standard develope ...

, C++, and

Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

. In target platforms, ingesting SPIR-V removes the need to build a high-level language source compiler into device drivers, which reduces driver complexity.

Versions

SPIR was originally introduced in 2011 and SPIR-V was introduced in 2015.

LLVM-based versions

SPIR prior to the 2015 SPIR-V release was based on the

LLVM Intermediate Representation LLVM, also called LLVM Core, is a target-independent optimizer and code generator. It can be used to develop a frontend for any programming language and a backend for any instruction set architecture. LLVM is designed around a language-indepen ...

. A provisional specification for SPIR 1.0 was announced in 2012. On July 22, 2013, a provisional specification SPIR 1.2 was announced at SIGGRAPH 2013. The final SPIR 1.2 specification was released at HiPEAC 2014 on January 21, 2014. On August 11, 2014, a provisional specification for SPIR 2.0 was released at SIGGRAPH 2014. SPIR-V does not use LLVM.

SPIR-V

SPIR-V 1.0 is a new version of SPIR announced in March 2015, and released on November 16, 2015. The SPIR family now includes a true cross-API standard that is fully defined by Khronos with native support for shader and kernel features. A separate program by the Khronos Group allows for interconversion with LLVM IR. Support for ingestion of SPIR-V is incorporated in the core specification of OpenCL 2.1, the Vulkan API, and

OpenGL OpenGL (Open Graphics Library) is a Language-independent specification, cross-language, cross-platform application programming interface (API) for rendering 2D computer graphics, 2D and 3D computer graphics, 3D vector graphics. The API is typic ...

version 4.6.

Features

SPIR-V is a high-level intermediate language, exchanged in binary form. Functions are represented by a

control-flow graph In computer science, a control-flow graph (CFG) is a representation, using graph notation, of all paths that might be traversed through a program during its execution. The control-flow graph was conceived by Frances E. Allen, who noted that ...

of basic blocks, using

static single assignment In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a type of intermediate representation (IR) where each variable is assigned exactly once. SSA is used in most high-quality optimizing compilers for ...

(SSA) form. Data structures retain high-level hierarchical representation. It is not lossy like previous byte-code or virtual machine-like intermediate representations used for graphical shaders. This allows closer to optimum performance on the target devices.

Extensibility

SPIR-V can be extended by writing extensions to add semantics, or reserving ranges of the token values for the party's use. Vendors can independently add desired semantics to SPIR-V. Additional sets of extended instruction sets can be provided in separate specifications. Multiple sets can be imported without issue, as extended instructions are used by specifying the ID of the set and of the instruction within the set.

Shaders

Debuggers include RenderDoc, SwiftShader, and Amber. Graphical shaders use structured control flow in SPIR-V to state how control flow nests. This helps in defining divergence and reconvergence of control flow on parallel execution environments. Specialization reduces the number of variants of a shader that need to be distributed.

Validation

The SPIR-V specification states the rules that must be followed to have a valid SPIR-V module. This allows for offline validation. Drivers are not obligated to handle invalid SPIR-V modules. In testing, conformance testing verifies that drivers behave correctly when consuming valid SPIR-V, while validators verify that front-ends properly generate SPIR-V.

Linking

SPIR-V can express calls to functions in a different compilation unit. The standard version of SPIR-V uses this feature for OpenCL compute kernels, but not for shader stages, which the graphical APIs want fully linked into a single SPIR-V module. There are extensions available to allow tools to temporarily use partially linked shaders and also kernels.

Capabilities

A SPIR-V module is used by a client API to support that module's features, which are classified through capabilities, and declared early in the module. A validator can confirm that the module uses only its declared capabilities, and a client API can reject modules that declare unsupported capabilities.

SPIR-V for GLSL cross-compilation

SPIR-V has been used to help deal with multiple versions of source-level languages. For example, the multiple versions of OpenGL Shading Language (GLSL) require distribution of multiple versions of shaders, due to implementations that are pegged to a specific older version of GLSL, such as for WebGL 1.0 and Apple's OpenGL implementation. One of the notable use cases of SPIR-V is its ability to be used as an interchange format between GLSL versions, using tools maintained by the

for compiling GLSL to SPIR-V glslangValidator, optimizing SPIR-V spirv-opt, and cross-compiling to SPIR-V to different GLSL targets spirv-cross. As a format, however, SPIR-V has some limitations for cross-compilation, including the requirement that every SPIR-V module have at least one entry-point symbol. This prevents the format from being easily used for separate compilation, where complex shaders could be assembled by a series of partial compile steps followed by a linking step. This runs counter to the stated goals of some SPIR-V tools such as spirv-link, which aims to provide full linking functionality for SPIR-V binary code.

References

External links

Khronos SPIR webpage

{{Khronos Group standards Compiler construction Shading languages