llvm_fprintf.rb

require 'llvm/core'
require 'llvm/analysis'
require 'llvm/execution_engine'

mod = LLVM::Module.new("test.fprintf")

str = "value = %d\n"

V_STRING = mod.globals.add(LLVM::Array(LLVM::Int8, str.size + 1), "str") do |value|
           value.linkage         = :internal
           value.unnamed_addr    = true
           value.global_constant = 1
           value.initializer     = LLVM::ConstantArray.string(str)
         end

# int fprintf(T_FILE * restrict stream, const char * restrict format, ...);
T_FILE = LLVM::Type.struct([], false, "struct.FILE")

V_STDERR = mod.globals.add(LLVM::Pointer(T_FILE), "__stderrp"); # Mac OS X 10.9

fprintf = mod.functions.add("fprintf", [T_FILE.pointer, LLVM::Pointer(LLVM::Int8)], LLVM::Int, :varargs => true) do |fn, stream, format|
            stream.name = "stream"
            format.name = "format"
            fn.add_attribute(:no_unwind_attribute)
          end

mod.functions.add("main", [], LLVM::Int) do |fn|
  fn.basic_blocks.append.build do |builder|
    format = builder.gep(V_STRING, [LLVM::Int(0), LLVM::Int(0)])
    stream = builder.load(V_STDERR)
    builder.call(fprintf, stream, format, LLVM::Int(rand 1000))
    builder.ret LLVM::Int(0)
  end
end

mod.verify!
mod.dump

# ; ModuleID = 'test.fprintf'
# 
# %struct.FILE = type opaque
# 
# @str = internal unnamed_addr constant [12 x i8] c"value = %d\0A\00"
# @__stderrp = external global %struct.FILE*
# 
# ; Function Attrs: nounwind
# declare i32 @fprintf(%struct.FILE*, i8*, ...) #0
# 
# define i32 @main() {
#   %1 = load %struct.FILE** @__stderrp
#   %2 = call i32 (%struct.FILE*, i8*, ...)* @fprintf(%struct.FILE* %1, i8* getelementptr inbounds ([12 x i8]* @str, i32 0, i32 0), i32 406)
#   ret i32 0
# }
# 
# attributes #0 = { nounwind }

# ---- JIT
LLVM.init_jit

engine = LLVM::JITCompiler.new(mod)
engine.run_function(mod.functions["main"])