Leaven: Compile LLVM IR to Go

Leaven translates LLVM intermediate representation to Go. In theory, it should be able to transpile any language that has an LLVM-based compiler to Go. But so far I’ve only used it for C.

Each LLVM instruction is translated to an equivalent statement in Go. This produces very verbose code; if you are looking for a tool that will convert a C codebase into maintainable Go, Leaven isn’t it.

But it does allow you to call C code from Go without using CGo. And I am hoping that it can produce a working Go translation of a program, which will be a good starting point for incrementally re-translating it (probably by hand) into idiomatic Go.

Warning

This software is incomplete and experimental. It does not support nearly all LLVM instructions.

The transpiler at github.com/andybalholm/c2go produces much better results (but it is not as automatic).

Usage Example

(Translating strcmp from musl libc.)

$ cat strcmp.c
#include <string.h>

int strcmp(const char *l, const char *r)
{
	for (; *l==*r && *l; l++, r++);
	return *(unsigned char *)l - *(unsigned char *)r;
}
$ clang -S -emit-llvm -fno-discard-value-names strcmp.c
$ leaven strcmp.ll
$ goimports -w strcmp.go
$ cat strcmp.go
package main

import "unsafe"

func strcmp(l *byte, r *byte) int32 {
	var l_addr, r_addr **byte
	var v0, v2, v4, v7, incdec_ptr, v8, incdec_ptr4, v9, v11 *byte
	var cmp, tobool, v6 bool
	var v1, v3, v5, v10, v12 byte
	var conv, conv1, conv3, conv5, conv6, sub int32

	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _ = l_addr, r_addr, v0, v1, conv, v2, v3, conv1, cmp, v4, v5, conv3, tobool, v6, v7, incdec_ptr, v8, incdec_ptr4, v9, v10, conv5, v11, v12, conv6, sub

	l_addr = new(*byte)
	r_addr = new(*byte)
	*l_addr = l
	*r_addr = r
	goto for_cond

for_cond:
	v0 = *l_addr
	v1 = *v0
	conv = int32(int8(v1))
	v2 = *r_addr
	v3 = *v2
	conv1 = int32(int8(v3))
	cmp = conv == conv1
	if cmp {
		goto land_rhs
	} else {
		v6 = false
		goto land_end
	}

land_rhs:
	v4 = *l_addr
	v5 = *v4
	conv3 = int32(int8(v5))
	tobool = conv3 != 0
	v6 = tobool
	goto land_end

land_end:
	if v6 {
		goto for_body
	} else {
		goto for_end
	}

for_body:
	goto for_inc

for_inc:
	v7 = *l_addr
	incdec_ptr = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(v7)) + 1*unsafe.Sizeof(*(*byte)(nil))))
	*l_addr = incdec_ptr
	v8 = *r_addr
	incdec_ptr4 = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(v8)) + 1*unsafe.Sizeof(*(*byte)(nil))))
	*r_addr = incdec_ptr4
	goto for_cond

for_end:
	v9 = *l_addr
	v10 = *v9
	conv5 = int32(uint32(v10))
	v11 = *r_addr
	v12 = *v11
	conv6 = int32(uint32(v12))
	sub = conv5 - conv6
	return sub
}