# IDE Setup for CUTLASS Development

This document outlines instructions and tips for setting up a local editor for CUTLASS development, including support
for intellisense, go-to-definition, code formatting, and so on.

## Overview
In order for any intellisense tool to work with CUTLASS, the following things need to be configured with it:
* Include paths, i.e. where the compiler (or in this case, the intellisense tool) should look for header files
* Compiler flags; especially the C++ standard (`--std`)
* Preprocessor variables; especially CUDA-related ones

One usually needs to configure the above variables in a settings file. Below, two config approaches are described:
for VSCode, and for any editor that uses the clangd language server, which includes
Vim, Emacs, NeoVim, Sublime Text, and so on. Note that VSCode can also be configured to use clangd.
It might be worth setting up clangd for VSCode rather than the default intellisense,
and you might see faster responses and more stable performance with clangd.

## VSCode Setup

1. Install the [Official C/C++ extension](https://marketplace.visualstudio.com/items?itemName=ms-vscode.cpptools)
1. Open settings...
    1. `Ctrl+Shift+P` to open the command palette
    1. Enter "C/C++" to filter results
    1. Select "C/C++ Edit Configurations (UI)" (or "... (JSON)" if you feel like editing the raw JSON)
    1. View the documentation for these settings
       [here](https://code.visualstudio.com/docs/cpp/c-cpp-properties-schema-reference)
1. Edit "Include Path" to set up **include paths**. For CUTLASS, this includes the following:
    * `${workspaceFolder}/include`
    * `${workspaceFolder}/tools/util/include`
    * `${workspaceFolder}/examples/common`
    * ...others, depending on which files you edit
1. Edit C++ standard to be `c++17`, `gnu++17`, or equivalent.
1. Edit `defines` to define preprocessor variables. See
[Global Config below](#global-config) for examples. The important
   ones include `__CUDACC_VER_MAJOR__`, `__CUDA_ARCH__`, `__CUDA_ARCH_FEAT_SM90_ALL__`. But configure
   them according to your target architecture.
1. ...and possible edit any other fields for your specific setup.

## clangd Setup

`clangd` is a C++ language server that is part of the LLVM project. You must first set it up your specific IDE:
* `clangd` official [documentation](https://clangd.llvm.org/installation#editor-plugins) for editor setup.
* NeoVim setup is possible through [lsp](https://neovim.io/doc/user/lsp.html) and either manually installing clangd or
using an installation manager like Mason.

Then, one needs to edit the config ([documentation](https://clangd.llvm.org/config)). One typically has a
**global** and a **per-project** config.

### Global Config

Here is one example for a global config.
On linux this is usually located at `~/.config/clangd/config.yaml` . Here is one example config for CUDA projects on SM90.
The key settings here are the preprocessor vars (`-D__CUDACC_VER_MAJOR__` , `-D__CUDA_ARCH__`)

```
CompileFlags:
  Compiler: /usr/local/cuda/bin/nvcc
  Add:
    - --cuda-path=/usr/local/cuda
    - --cuda-gpu-arch=sm_90a
    - -I/usr/local/cuda/include
    - "-xcuda"
    # report all errors
    - "-ferror-limit=0"
    - --cuda-gpu-arch=sm_90a
    - --std=c++17
    - "-D__INTELLISENSE__"
    - "-D__CLANGD__"
    - "-DCUDA_12_0_SM90_FEATURES_SUPPORTED"
    - "-DCUTLASS_ARCH_MMA_SM90_SUPPORTED=1"
    - "-D_LIBCUDACXX_STD_VER=12"
    - "-D__CUDACC_VER_MAJOR__=12"
    - "-D__CUDACC_VER_MINOR__=3"
    - "-D__CUDA_ARCH__=900"
    - "-D__CUDA_ARCH_FEAT_SM90_ALL"
    - "-Wno-invalid-constexpr"
  Remove:
    # strip CUDA fatbin args
    - "-Xfatbin*"
    # strip CUDA arch flags
    - "-gencode*"
    - "--generate-code*"
    # strip CUDA flags unknown to clang
    - "-ccbin*"
    - "--compiler-options*"
    - "--expt-extended-lambda"
    - "--expt-relaxed-constexpr"
    - "-forward-unknown-to-host-compiler"
    - "-Werror=cross-execution-space-call"
Hover:
  ShowAKA: No
InlayHints:
  Enabled: No
Diagnostics:
  Suppress:
    - "variadic_device_fn"
    - "attributes_not_allowed"
```

### Local Config
Local config is needed to specify per-project settings, especially include paths. An example is:
```
CompileFlags:
  Add:
    - -I</absolute/path/to/cutlass>/include/
    - -I</absolute/path/to/cutlass>/tools/util/include/
    - -I</absolute/path/to/cutlass>/cutlass/examples/common/
```

Note that absolute paths are needed since clangd doesn't support relative paths.

### Note on compile_commands.json
For typical C++ projects, clangd can *automatically* configure itself by parsing the `compile_commands.json`
generated by your CMake build. The path to such a file is by default `build/compile_commands.json` and is
configured by the `CompilationDatabase` config.

This is usually a convenient way to configure projects, but it's not as simple for CUDA/nvcc projects, since
clang doesn't understand many of the compiler flags used by nvcc. Hence, for now, we don't recommend using
`compile_commands.json` to configure your CUDA project.

### Copyright

Copyright (c) 2017 - 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
SPDX-License-Identifier: BSD-3-Clause

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