// This example produces LLVM IR code equivalent to the following C code,
// which implements a pseudo-random number generator.
//
//    int abs(int x);
//
//    int seed = 0;
//
//    // ref: https://en.wikipedia.org/wiki/Linear_congruential_generator
//    //    a = 0x15A4E35
//    //    c = 1
//    int rand(void) {
//       seed = seed*0x15A4E35 + 1;
//       return abs(seed);
//    }

// Create convenience types and constants.
i32 := types.I32
zero := constant.NewInt(0, i32)
a := constant.NewInt(0x15A4E35, i32) // multiplier of the PRNG.
c := constant.NewInt(1, i32)         // increment of the PRNG.

// Create a new LLVM IR module.
m := ir.NewModule()

// Create an external function declaration and append it to the module.
//
//    int abs(int x);
abs := m.NewFunction("abs", i32, ir.NewParam("x", i32))

// Create a global variable definition and append it to the module.
//
//    int seed = 0;
seed := m.NewGlobalDef("seed", zero)

// Create a function definition and append it to the module.
//
//    int rand(void) { ... }
rand := m.NewFunction("rand", i32)

// Create an unnamed entry basic block and append it to the `rand` function.
entry := rand.NewBlock("")

// Create instructions and append them to the entry basic block.
tmp1 := entry.NewLoad(seed)
tmp2 := entry.NewMul(tmp1, a)
tmp3 := entry.NewAdd(tmp2, c)
entry.NewStore(tmp3, seed)
tmp4 := entry.NewCall(abs, tmp3)
entry.NewRet(tmp4)

// Print the LLVM IR assembly of the module.
fmt.Println(m)

// Parse the LLVM IR assembly file `rand.ll`.
m, err := asm.ParseFile("testdata/rand.ll")
if err != nil {
    log.Fatal(err)
}
// Pretty-print the data types of the parsed LLVM IR module.
pretty.Println(m)

package main

import (
    "fmt"
    "log"

    "github.com/llir/llvm/asm"
    "github.com/llir/llvm/ir"
    "github.com/llir/llvm/ir/constant"
    "github.com/llir/llvm/ir/types"
    "github.com/llir/llvm/ir/value"
)

func main() {
    // Parse the LLVM IR assembly file `eval.ll`.
    m, err := asm.ParseFile("testdata/eval.ll")
    if err != nil {
        log.Fatal(err)
    }
    // Evalute and print the return value of the `@main` function.
    for _, f := range m.Funcs {
        if f.Name == "main" {
            e := newEvaluator(f)
            fmt.Println("result:", e.eval())
            break
        }
    }
}

// evaluator is a function evaluator.
type evaluator struct {
    // Function.
    f *ir.Function
    // Function arguments.
    args []value.Value
}

// newEvaluator returns a new function evaluator, for evaluating the result of
// invoking f with args.
func newEvaluator(f *ir.Function, args ...value.Value) *evaluator {
    return &evaluator{f: f, args: args}
}

// eval evalutes f and returns the corresponding 32-bit integer.
func (e *evaluator) eval() uint32 {
    f := e.f
    if !types.Equal(f.Sig.Ret, types.I32) {
        panic(fmt.Errorf("support for function return type %v not yet implemented", f.Sig.Ret))
    }
    for _, block := range f.Blocks {
        switch term := block.Term.(type) {
        case *ir.TermRet:
            // NOTE: support for functions with more than one RET terminator not
            // yet implemented.
            if term.X != nil {
                // Evaluate the result of the first return value of a function is
                // evaluated.
                return e.evalValue(term.X)
            }
        }
    }
    panic(fmt.Errorf("unable to locate RET terminator in function %q", f.Name))
}

// evalInst evaluates inst and returns the corresponding 32-bit integer.
func (e *evaluator) evalInst(inst ir.Instruction) uint32 {
    switch inst := inst.(type) {
    // Binary instructions.
    case *ir.InstAdd:
        return e.evalValue(inst.X) + e.evalValue(inst.Y)
    case *ir.InstSub:
        return e.evalValue(inst.X) - e.evalValue(inst.Y)
    case *ir.InstMul:
        return e.evalValue(inst.X) * e.evalValue(inst.Y)
    case *ir.InstUDiv:
        return e.evalValue(inst.X) / e.evalValue(inst.Y)
    case *ir.InstSDiv:
        return e.evalValue(inst.X) / e.evalValue(inst.Y)
    case *ir.InstURem:
        return e.evalValue(inst.X) % e.evalValue(inst.Y)
    case *ir.InstSRem:
        return e.evalValue(inst.X) % e.evalValue(inst.Y)
    // Bitwise instructions.
    case *ir.InstShl:
        return e.evalValue(inst.X) << e.evalValue(inst.Y)
    case *ir.InstLShr:
        return e.evalValue(inst.X) >> e.evalValue(inst.Y)
    case *ir.InstAShr:
        x, y := e.evalValue(inst.X), e.evalValue(inst.Y)
        result := x >> y
        if x&0x80000000 != 0 {
            for i := uint32(31); i >= 0; i-- {
                mask := uint32(1 << i)
                if result&mask != 0 {
                    break
                }
                result |= mask
            }
        }
        return result
    case *ir.InstAnd:
        return e.evalValue(inst.X) & e.evalValue(inst.Y)
    case *ir.InstOr:
        return e.evalValue(inst.X) | e.evalValue(inst.Y)
    case *ir.InstXor:
        return e.evalValue(inst.X) ^ e.evalValue(inst.Y)
    // Other instructions.
    case *ir.InstCall:
        callee, ok := inst.Callee.(*ir.Function)
        if !ok {
            panic(fmt.Errorf("support for callee of type %T not yet implemented", inst.Callee))
        }
        ee := newEvaluator(callee, inst.Args...)
        return ee.eval()
    default:
        panic(fmt.Errorf("support for instruction type %T not yet implemented", inst))
    }
}

// evalValue evalutes v and returns the corresponding 32-bit integer.
func (e *evaluator) evalValue(v value.Value) uint32 {
    switch v := v.(type) {
    case ir.Instruction:
        return e.evalInst(v)
    case *constant.Int:
        return uint32(v.X.Int64())
    case *types.Param:
        if len(v.Name) == 0 {
            panic("support for unnamed parameters not yet implemented")
        }
        f := e.f
        for i, param := range f.Sig.Params {
            if v.Name == param.Name {
                return e.evalValue(e.args[i])
            }
        }
        panic(fmt.Errorf("unable to locate paramater %q of function %q", v.Name, f.Name))
    default:
        panic(fmt.Errorf("support for value type %T not yet implemented", v))
    }
}