llgo - A Go compiler based on LLVM
=====

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LLGo is a Go compiler based on LLVM in order to better integrate Go with the C ecosystem including Python. It's a subproject of [the Go+ project](https://github.com/goplus/gop).


## C standard libary support

```go
package main

import "github.com/goplus/llgo/c"

func main() {
	c.Printf(c.Str("Hello world\n"))
}
```

This is a simple example of calling the C `printf` function to print `Hello world`. Here, `c.Str` is not a function for converting a Go string to a C string, but a built-in instruction supported by `llgo` for generating a C string constant.

The `_demo` directory contains some C standard libary related demos (it start with `_` to prevent the `go` command from compiling it):

* [hello](_demo/hello/hello.go): call C `printf` to print `Hello world`
* [concat](_demo/concat/concat.go): call C `fprintf` with `stderr`
* [qsort](_demo/qsort/qsort.go): call C function with a callback (eg. `qsort`)

To run these demos (If you haven't installed `llgo` yet, please refer to [How to install](#how-to-install)):

```sh
export LLGOROOT=`pwd`
cd <demo-directory>  # eg. cd _demo/hello
llgo run .
```

See [github.com/goplus/llgo/c](https://pkg.go.dev/github.com/goplus/llgo/c) for more detials.


## Python support

You can import a Python library in LLGo!

And you can import any Python library into `llgo` through a program called `llpyg` (see [Development tools](#development-tools)). The currently imported libraries include:

* [sys](https://pkg.go.dev/github.com/goplus/llgo/py/sys)
* [os](https://pkg.go.dev/github.com/goplus/llgo/py/os)
* [math](https://pkg.go.dev/github.com/goplus/llgo/py/math)
* [json](https://pkg.go.dev/github.com/goplus/llgo/py/json)
* [inspect](https://pkg.go.dev/github.com/goplus/llgo/py/inspect)
* [statistics](https://pkg.go.dev/github.com/goplus/llgo/py/statistics)
* [numpy](https://pkg.go.dev/github.com/goplus/llgo/py/numpy)

Here is an example using the Python `math` library:

```go
package main

import (
	"github.com/goplus/llgo/c"
	"github.com/goplus/llgo/py"
	"github.com/goplus/llgo/py/math"
)

func main() {
	x := math.Sqrt(py.Float(2))
	c.Printf(c.Str("sqrt(2) = %f\n"), x.Float64())
}
```

Here, We call `py.Float(2)` to create a Python number 2, and pass it to Python’s `math.sqrt` to get `x`. Then use `x.Float64()` to convert x to Go's `float64` type, and print the value through the C `printf` function.

Let's look at a slightly more complex example. For example, we use `numpy` to calculate:

```go
package main

import (
	"github.com/goplus/llgo/c"
	"github.com/goplus/llgo/py"
	"github.com/goplus/llgo/py/numpy"
)

func main() {
	a := py.List(
		py.List(1.0, 2.0, 3.0),
		py.List(4.0, 5.0, 6.0),
		py.List(7.0, 8.0, 9.0),
	)
	b := py.List(
		py.List(9.0, 8.0, 7.0),
		py.List(6.0, 5.0, 4.0),
		py.List(3.0, 2.0, 1.0),
	)
	x := numpy.Add(a, b)
	c.Printf(c.Str("a+b = %s\n"), x.Str().CStr())
}
```

Here we define two 3x3 matrices a and b, add them to get x, and then print the result.

The `_pydemo` directory contains some python related demos:

* [callpy](_pydemo/callpy/callpy.go): call Python standard library function `math.sqrt`
* [pi](_pydemo/pi/pi.go): print python constants `math.pi`
* [statistics](_pydemo/statistics/statistics.go): define a python list and call `statistics.mean` to get the mean
* [matrix](_pydemo/matrix/matrix.go): a basic `numpy` demo

To run these demos, you need to set the `LLGO_LIB_PYTHON` environment variable first.

If Python is in the search path for `clang` linking, then `LLGO_LIB_PYTHON` only needs to be set to the name of the Python library. For example:

```sh
export LLGO_LIB_PYTHON=python3.12
```

You can also specify the path to tell `llgo` where the Python library is located:

```sh
export LLGO_LIB_PYTHON=/foo/bar/python3.12
```

For example, `/opt/homebrew/Frameworks/Python.framework/Versions/3.12/libpython3.12.dylib` is a typical python library location under macOS. So we should set it like this:

```sh
export LLGO_LIB_PYTHON=/opt/homebrew/Frameworks/Python.framework/Versions/3.12/python3.12
```

Note that the file name must be written in a platform-independent format, using `python3.12` instead of `libpython3.12.dylib`.

Then you can run the demos:

```sh
export LLGOROOT=`pwd`
cd <demo-directory>  # eg. cd _pydemo/callpy
llgo run .
```

See [github.com/goplus/llgo/py](https://pkg.go.dev/github.com/goplus/llgo/py) for more detials.


## Other frequently used libraries

LLGo can easily import any libraries from the C ecosystem. Currently, this import process is still manual, but in the future, it will be automated similar to Python library imports.

The currently imported libraries include:

* [llama2.c](https://pkg.go.dev/github.com/goplus/llgo/c/llama2)
* [cjson](https://pkg.go.dev/github.com/goplus/llgo/c/cjson)
* [sqlite](https://pkg.go.dev/github.com/goplus/llgo/c/sqlite)

Here are some examples related to them:

* [llama2-c](_demo/llama2-c): inference Llama 2 (It's the first llgo AI example)
* [mkjson](c/cjson/_demo/mkjson/mkjson.go): create a json object and print it
* [sqlitedemo](c/sqlite/_demo/sqlitedemo/demo.go): a basic sqlite demo


## Go syntax support

The priority of `llgo` feature iteration is:

* Popular C/Python libraries
* Full Go syntax
* Go standard libraries
* Popular Go packages

Common Go syntax is already supported. Except for the following, which needs to be improved:

* interface (Limited support)
* map (Very limited support)
* panic (Limited support)
* recover (Not supported yet)
* defer (Not supported yet)
* gc (Not supported yet)
* chan (Not supported yet)
* goroutine (Not supported yet)
* generics (Not supported yet)

Here are some examples related to Go syntax:

* [concat](_demo/concat/concat.go): define a variadic function
* [genints](_demo/genints/genints.go): various forms of closure usage (including C function, recv.method and anonymous function)


## How to install

Follow these steps to generate the `llgo` command (its usage is the same as the `go` command):

### on macOS

```sh
brew update  # execute if needed
brew install llvm@17
go install -v ./...
```

### on Linux

```sh
echo 'deb http://apt.llvm.org/focal/ llvm-toolchain-focal-17 main' | sudo tee /etc/apt/sources.list.d/llvm.list
wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
sudo apt-get update  # execute if needed
sudo apt-get install --no-install-recommends llvm-17-dev
go install -v ./...
```

### on Windows

TODO


## Development tools

* [pydump](chore/_xtool/pydump): It's the first program compiled by `llgo` (NOT `go`) in a production environment. It outputs symbol information (functions, variables, and constants) from a Python library in JSON format, preparing for the generation of corresponding packages in `llgo`.
* [llpyg](chore/llpyg): It is used to automatically convert Python libraries into Go packages that `llgo` can import. It depends on `pydump` to accomplish the task.
* [llgen](chore/llgen): It is used to compile Go packages into LLVM IR files (*.ll).
* [ssadump](chore/ssadump): It is a Go SSA builder and interpreter.

How do I generate these tools?

```sh
go install -v ./...  # compile all tools except pydump
cd chore/_xtool
llgo install ./...   # compile pydump
```

## Key modules

Below are the key modules for understanding the implementation principles of `llgo`:

* [llgo/ssa](https://pkg.go.dev/github.com/goplus/llgo/ssa): It generates LLVM IR files (LLVM SSA) using the semantics (interfaces) of Go SSA. Although `LLVM SSA` and `Go SSA` are both IR languages, they work at completely different levels. `LLVM SSA` is closer to machine code, which abstracts different instruction sets. While `Go SSA` is closer to a high-level language. We can think of it as the instruction set of the `Go computer`. `llgo/ssa` is not just limited to the `llgo` compiler. If we view it as the high-level expressive power of `LLVM`, you'll find it very useful. Prior to `llgo/ssa`, you had to operate `LLVM` using machine code semantics. But now, with the advanced SSA form (in the semantics of Go SSA), you can conveniently utilize `LLVM`.
* [llgo/cl](https://pkg.go.dev/github.com/goplus/llgo/cl): It is the core of the llgo compiler. It converts a Go package into LLVM IR files. It depends on `llgo/ssa`.
* [llgo/internal/build](https://pkg.go.dev/github.com/goplus/llgo/internal/build): It strings together the entire compilation process of `llgo`. It depends on `llgo/ssa` and `llgo/cl`.