User Guide for the DirectX Target — LLVM 22.1.6 documentation

# User Guide for the DirectX Target

Warning

Disclaimer: The DirectX backend is experimental and under active development. It is not yet feature complete or ready to be used outside of experimental or demonstration contexts.

## Introduction

The DirectX target implements the DirectX programmability interfaces. These interfaces are documented in the DirectX Specifications.

Initially the backend is aimed at supporting DirectX 12, and support for DirectX 11 is planned at a later date.

The DirectX backend is currently experimental and is not shipped with any release builds of LLVM tools. To build the DirectX backend locally, add `DirectX` to the `LLVM_EXPERIMENTAL_TARGETS_TO_BUILD` CMake option. For more information on building LLVM see the Building LLVM with CMake documentation.

## Target Triples

At present, the DirectX target only supports the `dxil` architecture, which generates code for the DirectX Intermediate Language.

In addition to target architecture, the DirectX backend also needs to know the target runtime version and pipeline stage. These are expressed using the OS and Environment triple component.

Presently, the DirectX backend requires targeting the `shadermodel` OS, and supports versions 6.0+ (as of writing, the latest announced version is 6.7).

Table 129 DirectX Environments
Environment | Description
--- | ---
`pixel` | Pixel shader
`vertex` | Vertex shader
`geometry` | Geometry shader
`hull` | Hull shader (tesselation)
`domain` | Domain shader (tesselation)
`compute` | Compute kernel
`library` | Linkable `dxil` library
`raygeneration` | Ray generation (ray tracing)
`intersection` | Ray intersection (ray tracing)
`anyhit` | Ray any collision (ray tracing)
`closesthit` | Ray closest collision (ray tracing)
`miss` | Ray miss (ray tracing)
`callable` | Callable shader (ray tracing)
`mesh` | Mesh shader
`amplification` | Amplification shader

## Output Binaries

The DirectX runtime APIs read a file format based on the DirectX Specification.. In different codebases the file format is referred to by different names (specifically `DXBC` and `DXILContainer`). Since the format is used to store both `DXBC` and `DXIL` outputs, and the ultimate goal is to support both as code generation targets in LLVM, the LLVM codebase uses a more neutral name, `DXContainer`.

The `DXContainer` format is sparsely documented in the functional specification, but a reference implementation exists in the DirectXShaderCompiler.. The format is documented in the LLVM project docs as well (see DirectX Container).

Support for generating `DXContainer` files in LLVM, is being added to the LLVM MC layer for object streamers and writers, and to the Object and ObjectYAML libraries for testing and object file tooling.

For `dxil` targeting, bitcode emission into `DXContainer` files follows a similar model to the `-fembed-bitcode` flag supported by clang for other targets.