ruby-llvm factorial example using MCJIT

factorial_mcjit.rb

require 'ffi'
require 'llvm/core'
require 'llvm/execution_engine'
require 'llvm/target'

# Start the "engine" before driving
# call InitializeNativeTargetAsmPrinter and InitializeNativeTargetAsmParser
LLVM::Target.init_native(true)

LLVM::C.link_in_mcjit

# modules hold functions and variables
mod = LLVM::Module.new('Factorial.mcjit')

fun = 
  mod.functions.add("fac", [LLVM::Int], LLVM::Int) do |fac, n|
    n.name    = "n"
    entry     = fac.basic_blocks.append("entry")
    recur     = fac.basic_blocks.append("recur")
    result    = fac.basic_blocks.append("result")
    n_fac_n_1 = nil # predeclare within function's scope

    entry.build do |b|
      test = b.icmp(:eq, n, LLVM::Int(1), "test")
      b.cond(test, result, recur)
    end

    recur.build do |b|
      n_1       = b.sub(n, LLVM::Int(1), "n-1")
      fac_n_1   = b.call(fac, n_1, "fac(n-1)")
      n_fac_n_1 = b.mul(n, fac_n_1, "n*fac(n-1)")
      b.br(result)
    end

    result.build do |b|
      fac = b.phi(LLVM::Int,
                 { entry => LLVM::Int(1),
                   recur => n_fac_n_1 },
                 "fac")
      b.ret(fac)
    end
  end

mod.verify
mod.dump

# MCJIT
execution_engine =
  FFI::MemoryPointer.new(:pointer) do |ptr|
    error  = FFI::MemoryPointer.new(:pointer)
    status = LLVM::C.create_mcjit_compiler_for_module(ptr, mod, nil, 0, error)

    unless status.zero?
      errorp  = error.read_pointer
      message = errorp.read_string unless errorp.null?
      LLVM::C.dispose_message(error)
      error.autorelease=false
      raise RuntimeError, "Error creating JIT compiler: #{message}"
    end
  end

execution_engine = execution_engine.read_pointer

# Run function
fac_n = ARGV[0] || 15

LLVM::C.get_pointer_to_global(execution_engine, fun).tap do |ptr|
  fn  = FFI::Function.new(:int, [:int], ptr)
  fac = fn.call(fac_n)
  puts "fac(#{fac_n}) = #{fac}"
end

LLVM::C.dispose_execution_engine(execution_engine)