tinygo/tgo.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"go/build"
	"go/constant"
	"go/token"
	"go/types"
	"os"
	"sort"
	"strings"

	"golang.org/x/tools/go/loader"
	"golang.org/x/tools/go/ssa"
	"golang.org/x/tools/go/ssa/ssautil"
	"llvm.org/llvm/bindings/go/llvm"
)

func init() {
	llvm.InitializeAllTargets()
	llvm.InitializeAllTargetMCs()
	llvm.InitializeAllTargetInfos()
	llvm.InitializeAllAsmParsers()
	llvm.InitializeAllAsmPrinters()
}

type Compiler struct {
	triple          string
	mod             llvm.Module
	ctx             llvm.Context
	builder         llvm.Builder
	machine         llvm.TargetMachine
	targetData      llvm.TargetData
	intType         llvm.Type
	uintptrType     llvm.Type
	stringLenType   llvm.Type
	stringType      llvm.Type
	interfaceType   llvm.Type
	typeassertType  llvm.Type
	itfTypeNumbers  map[types.Type]uint64
	itfTypes        []types.Type
	initFuncs       []llvm.Value
}

type Frame struct {
	llvmFn llvm.Value
	params map[*ssa.Parameter]int   // arguments to the function
	locals map[ssa.Value]llvm.Value // local variables
	blocks map[*ssa.BasicBlock]llvm.BasicBlock
	phis   []Phi
}

func pkgPrefix(pkg *ssa.Package) string {
	if pkg.Pkg.Name() == "main" {
		return "main"
	}
	return pkg.Pkg.Path()
}

type Phi struct {
	ssa  *ssa.Phi
	llvm llvm.Value
}

func NewCompiler(pkgName, triple string) (*Compiler, error) {
	c := &Compiler{
		triple:         triple,
		itfTypeNumbers: make(map[types.Type]uint64),
	}

	target, err := llvm.GetTargetFromTriple(triple)
	if err != nil {
		return nil, err
	}
	c.machine = target.CreateTargetMachine(triple, "", "", llvm.CodeGenLevelDefault, llvm.RelocDefault, llvm.CodeModelDefault)
	c.targetData = c.machine.CreateTargetData()

	c.mod = llvm.NewModule(pkgName)
	c.ctx = c.mod.Context()
	c.builder = c.ctx.NewBuilder()

	// Depends on platform (32bit or 64bit), but fix it here for now.
	c.intType = llvm.Int32Type()
	c.stringLenType = llvm.Int32Type()
	c.uintptrType = c.targetData.IntPtrType()

	// Go string: tuple of (len, ptr)
	c.stringType = llvm.StructType([]llvm.Type{c.stringLenType, llvm.PointerType(llvm.Int8Type(), 0)}, false)

	// Go interface: tuple of (type, ptr)
	c.interfaceType = llvm.StructType([]llvm.Type{llvm.Int32Type(), llvm.PointerType(llvm.Int8Type(), 0)}, false)

	// Go typeassert result: tuple of (ptr, bool)
	c.typeassertType = llvm.StructType([]llvm.Type{llvm.PointerType(llvm.Int8Type(), 0), llvm.Int1Type()}, false)

	return c, nil
}

func (c *Compiler) Parse(mainPath string, buildTags []string) error {
	tripleSplit := strings.Split(c.triple, "-")

	config := loader.Config {
		// TODO: TypeChecker.Sizes
		Build: &build.Context {
			GOARCH:      tripleSplit[0],
			GOOS:        tripleSplit[2],
			GOROOT:      ".",
			CgoEnabled:  true,
			UseAllFiles: false,
			Compiler:    "gc", // must be one of the recognized compilers
			BuildTags:   append([]string{"tgo"}, buildTags...),
		},
		AllowErrors: true,
	}
	config.Import("runtime")
	config.Import(mainPath)
	lprogram, err := config.Load()
	if err != nil {
		return err
	}

	// TODO: pick the error of the first package, not a random package
	for _, pkgInfo := range lprogram.AllPackages {
		fmt.Println("package:", pkgInfo.Pkg.Name())
		if len(pkgInfo.Errors) != 0 {
			return pkgInfo.Errors[0]
		}
	}

	program := ssautil.CreateProgram(lprogram, ssa.SanityCheckFunctions | ssa.BareInits)
	program.Build()

	// Make a list of packages in import order.
	packageList := []*ssa.Package{}
	packageSet := map[string]struct{}{}
	worklist := [][]string{{"runtime", mainPath}}
	for len(worklist) != 0 {
		for _, pkgPath := range worklist[0] {
			pkg := program.ImportedPackage(pkgPath)
			if pkg == nil {
				packageSet[pkgPath] = struct{}{}
				continue // non-SSA package (e.g. cgo)
			}
			if _, ok := packageSet[pkgPath]; ok {
				continue
			}

			unsatisfiedImports := make([]string, 0)
			imports := pkg.Pkg.Imports()
			if pkgPath != "runtime" && pkgPath != "unsafe" && pkgPath != "runtime/cgo" && pkgPath != "syscall" {
				imports = append(imports, program.ImportedPackage("runtime").Pkg)
			}
			for _, pkg := range imports {
				if _, ok := packageSet[pkg.Path()]; ok {
					continue
				}
				unsatisfiedImports = append(unsatisfiedImports, pkg.Path())
			}
			if len(unsatisfiedImports) == 0 {
				// all dependencies are in packageList inserted
				packageList = append(packageList, pkg)
				packageSet[pkgPath] = struct{}{}
			} else {
				unsatisfiedImports = append(unsatisfiedImports, pkgPath) // reconsider
				worklist = append(worklist, unsatisfiedImports)
			}
		}
		worklist = worklist[1:]
	}

	// Transform each package into LLVM IR.
	for _, pkg := range packageList {
		err := c.parsePackage(program, pkg)
		if err != nil {
			return err
		}
	}

	// After all packages are imported, add a synthetic initializer function
	// that calls the initializer of each package.
	initType := llvm.FunctionType(llvm.VoidType(), nil, false)
	initFn := llvm.AddFunction(c.mod, "runtime.initAll", initType)
	block := c.ctx.AddBasicBlock(initFn, "entry")
	c.builder.SetInsertPointAtEnd(block)
	for _, fn := range c.initFuncs {
		c.builder.CreateCall(fn, nil, "")
	}
	c.builder.CreateRetVoid()

	return nil
}

func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
	fmt.Println("        type:", goType)
	switch typ := goType.(type) {
	case *types.Array:
		elemType, err := c.getLLVMType(typ.Elem())
		if err != nil {
			return llvm.Type{}, err
		}
		return llvm.ArrayType(elemType, int(typ.Len())), nil
	case *types.Basic:
		switch typ.Kind() {
		case types.Bool:
			return llvm.Int1Type(), nil
		case types.Int8, types.Uint8:
			return llvm.Int8Type(), nil
		case types.Int16, types.Uint16:
			return llvm.Int16Type(), nil
		case types.Int32, types.Uint32:
			return llvm.Int32Type(), nil
		case types.Int, types.Uint:
			return c.intType, nil
		case types.Int64, types.Uint64:
			return llvm.Int64Type(), nil
		case types.String:
			return c.stringType, nil
		case types.Uintptr:
			return c.uintptrType, nil
		case types.UnsafePointer:
			return llvm.PointerType(llvm.Int8Type(), 0), nil
		default:
			return llvm.Type{}, errors.New("todo: unknown basic type: " + fmt.Sprintf("%#v", typ))
		}
	case *types.Interface:
		return c.interfaceType, nil
	case *types.Named:
		return c.getLLVMType(typ.Underlying())
	case *types.Pointer:
		ptrTo, err := c.getLLVMType(typ.Elem())
		if err != nil {
			return llvm.Type{}, err
		}
		return llvm.PointerType(ptrTo, 0), nil
	case *types.Struct:
		members := make([]llvm.Type, typ.NumFields())
		for i := 0; i < typ.NumFields(); i++ {
			member, err := c.getLLVMType(typ.Field(i).Type())
			if err != nil {
				return llvm.Type{}, err
			}
			members[i] = member
		}
		return llvm.StructType(members, false), nil
	default:
		return llvm.Type{}, errors.New("todo: unknown type: " + fmt.Sprintf("%#v", goType))
	}
}

func (c *Compiler) getZeroValue(typ llvm.Type) (llvm.Value, error) {
	switch typ.TypeKind() {
	case llvm.ArrayTypeKind:
		subTyp := typ.ElementType()
		vals := make([]llvm.Value, typ.ArrayLength())
		for i := range vals {
			val, err := c.getZeroValue(subTyp)
			if err != nil {
				return llvm.Value{}, err
			}
			vals[i] = val
		}
		return llvm.ConstArray(subTyp, vals), nil
	case llvm.IntegerTypeKind:
		return llvm.ConstInt(typ, 0, false), nil
	case llvm.PointerTypeKind:
		return llvm.ConstPointerNull(typ), nil
	case llvm.StructTypeKind:
		types := typ.StructElementTypes()
		vals := make([]llvm.Value, len(types))
		for i, subTyp := range types {
			val, err := c.getZeroValue(subTyp)
			if err != nil {
				return llvm.Value{}, err
			}
			vals[i] = val
		}
		return llvm.ConstStruct(vals, false), nil
	default:
		return llvm.Value{}, errors.New("todo: LLVM zero initializer")
	}
}

func (c *Compiler) getInterfaceType(typ types.Type) llvm.Value {
	if _, ok := c.itfTypeNumbers[typ]; !ok {
		num := uint64(len(c.itfTypes))
		c.itfTypes = append(c.itfTypes, typ)
		c.itfTypeNumbers[typ] = num
	}
	return llvm.ConstInt(llvm.Int32Type(), c.itfTypeNumbers[typ], false)
}

func (c *Compiler) getFunctionName(fn *ssa.Function) string {
	if fn.Signature.Recv() != nil {
		// Method on a defined type.
		typeName := fn.Params[0].Type().(*types.Named).Obj().Name()
		return pkgPrefix(fn.Pkg) + "." + typeName + "." + fn.Name()
	} else {
		// Bare function.
		if strings.HasPrefix(fn.Name(), "_Cfunc_") {
			// Name CGo functions directly.
			return fn.Name()[len("_Cfunc_"):]
		} else {
			return pkgPrefix(fn.Pkg) + "." + fn.Name()
		}
	}
}

func (c *Compiler) parsePackage(program *ssa.Program, pkg *ssa.Package) error {
	fmt.Println("package:", pkg.Pkg.Path())

	// Make sure we're walking through all members in a constant order every
	// run.
	memberNames := make([]string, 0)
	for name := range pkg.Members {
		if strings.HasPrefix(name, "_Cgo_") || strings.HasPrefix(name, "_cgo") {
			// _Cgo_ptr, _Cgo_use, _cgoCheckResult, _cgo_runtime_cgocall
			continue // CGo-internal functions
		}
		if strings.HasPrefix(name, "__cgofn__cgo_") {
			continue // CGo function pointer in global scope
		}
		memberNames = append(memberNames, name)
	}
	sort.Strings(memberNames)

	frames := make(map[*ssa.Function]*Frame)

	// First, build all function declarations.
	for _, name := range memberNames {
		member := pkg.Members[name]

		switch member := member.(type) {
		case *ssa.Function:
			frame, err := c.parseFuncDecl(member)
			if err != nil {
				return err
			}
			frames[member] = frame
			if member.Synthetic == "package initializer" {
				c.initFuncs = append(c.initFuncs, frame.llvmFn)
			}
		case *ssa.NamedConst:
			// Ignore package-level untyped constants. The SSA form doesn't need
			// them.
		case *ssa.Global:
			typ := member.Type()
			if typPtr, ok := typ.(*types.Pointer); ok {
				typ = typPtr.Elem()
			} else {
				return errors.New("global is not a pointer")
			}
			llvmType, err := c.getLLVMType(typ)
			if err != nil {
				return err
			}
			global := llvm.AddGlobal(c.mod, llvmType, pkgPrefix(member.Pkg) + "." +  member.Name())
			global.SetLinkage(llvm.PrivateLinkage)
			initializer, err := c.getZeroValue(llvmType)
			if err != nil {
				return err
			}
			global.SetInitializer(initializer)
		case *ssa.Type:
			ms := program.MethodSets.MethodSet(member.Type())
			for i := 0; i < ms.Len(); i++ {
				fn := program.MethodValue(ms.At(i))
				frame, err := c.parseFuncDecl(fn)
				if err != nil {
					return err
				}
				frames[fn] = frame
			}
		default:
			return errors.New("todo: member: " + fmt.Sprintf("%#v", member))
		}
	}

	// Now, add definitions to those declarations.
	for _, name := range memberNames {
		member := pkg.Members[name]
		fmt.Println("member:", member.Token(), member)

		switch member := member.(type) {
		case *ssa.Function:
			if strings.HasPrefix(name, "_Cfunc_") {
				// CGo function. Don't implement it's body.
				continue
			}
			if member.Blocks == nil {
				continue // external function
			}
			var err error
			if member.Synthetic == "package initializer" {
				err = c.parseInitFunc(frames[member], member)
			} else {
				err = c.parseFunc(frames[member], member)
			}
			if err != nil {
				return err
			}
		case *ssa.Type:
			ms := program.MethodSets.MethodSet(member.Type())
			for i := 0; i < ms.Len(); i++ {
				fn := program.MethodValue(ms.At(i))
				err := c.parseFunc(frames[fn], fn)
				if err != nil {
					return err
				}
			}
		}
	}

	return nil
}

func (c *Compiler) parseFuncDecl(f *ssa.Function) (*Frame, error) {
	f.WriteTo(os.Stdout)
	name := c.getFunctionName(f)

	frame := &Frame{
		params: make(map[*ssa.Parameter]int),
		locals: make(map[ssa.Value]llvm.Value),
		blocks: make(map[*ssa.BasicBlock]llvm.BasicBlock),
	}

	var retType llvm.Type
	if f.Signature.Results() == nil {
		retType = llvm.VoidType()
	} else if f.Signature.Results().Len() == 1 {
		var err error
		retType, err = c.getLLVMType(f.Signature.Results().At(0).Type())
		if err != nil {
			return nil, err
		}
	} else {
		return nil, errors.New("todo: return values")
	}

	var paramTypes []llvm.Type
	for i, param := range f.Params {
		paramType, err := c.getLLVMType(param.Type())
		if err != nil {
			return nil, err
		}
		paramTypes = append(paramTypes, paramType)
		frame.params[param] = i
	}

	fnType := llvm.FunctionType(retType, paramTypes, false)

	frame.llvmFn = c.mod.NamedFunction(name)
	if frame.llvmFn.IsNil() {
		frame.llvmFn = llvm.AddFunction(c.mod, name, fnType)
	}
	return frame, nil
}

// Special function parser for generated package initializers (which also
// initializes global variables).
func (c *Compiler) parseInitFunc(frame *Frame, f *ssa.Function) error {
	llvmBlock := c.ctx.AddBasicBlock(frame.llvmFn, "entry")
	c.builder.SetInsertPointAtEnd(llvmBlock)

	for _, block := range f.DomPreorder() {
		for _, instr := range block.Instrs {
			var err error
			switch instr := instr.(type) {
			case *ssa.Convert:
				// ignore: CGo pointer conversion
			case *ssa.Return:
				err = c.parseInstr(frame, instr)
			case *ssa.FieldAddr:
				// ignore
			case *ssa.Store:
				var llvmAddr llvm.Value
				switch addr := instr.Addr.(type) {
				case *ssa.Global:
					// Regular store, like a global int variable.
					if strings.HasPrefix(addr.Name(), "__cgofn__cgo_") || strings.HasPrefix(addr.Name(), "_cgo_") {
						// Ignore CGo global variables which we don't use.
						continue
					}
					val, err := c.parseExpr(frame, instr.Val)
					if err != nil {
						return err
					}
					fullName := pkgPrefix(addr.Pkg) + "." + addr.Name()
					llvmAddr = c.mod.NamedGlobal(fullName)
					llvmAddr.SetInitializer(val)
				case *ssa.FieldAddr:
					// Initialize field of a global struct.
					// LLVM does not allow setting an initializer on part of a
					// global variable. So we take the current initializer, add
					// the field, and replace the initializer with the new
					// initializer.
					val, err := c.parseExpr(frame, instr.Val)
					if err != nil {
						return err
					}
					global := addr.X.(*ssa.Global)
					llvmAddr := c.mod.NamedGlobal(pkgPrefix(global.Pkg) + "." + global.Name())
					llvmValue := llvmAddr.Initializer()
					llvmValue = c.builder.CreateInsertValue(llvmValue, val, addr.Field, "")
					llvmAddr.SetInitializer(llvmValue)
				default:
					return errors.New("unknown init store: " + fmt.Sprintf("%#v", addr))
				}
			default:
				return errors.New("unknown init instruction: " + fmt.Sprintf("%#v", instr))
			}
			if err != nil {
				return err
			}
		}
	}
	return nil
}

func (c *Compiler) parseFunc(frame *Frame, f *ssa.Function) error {
	if frame.llvmFn.Name() != "main.main" {
		// This function is only used from within Go.
		frame.llvmFn.SetLinkage(llvm.PrivateLinkage)
	}

	// Pre-create all basic blocks in the function.
	for _, block := range f.DomPreorder() {
		llvmBlock := c.ctx.AddBasicBlock(frame.llvmFn, block.Comment)
		frame.blocks[block] = llvmBlock
	}

	// Load function parameters
	for _, param := range f.Params {
		llvmParam := frame.llvmFn.Param(frame.params[param])
		frame.locals[param] = llvmParam
	}

	// Fill those blocks with instructions.
	for _, block := range f.DomPreorder() {
		c.builder.SetInsertPointAtEnd(frame.blocks[block])
		for _, instr := range block.Instrs {
			fmt.Printf("  instr: %v\n", instr)
			err := c.parseInstr(frame, instr)
			if err != nil {
				return err
			}
		}
	}

	// Resolve phi nodes
	for _, phi := range frame.phis {
		block := phi.ssa.Block()
		for i, edge := range phi.ssa.Edges {
			llvmVal, err := c.parseExpr(frame, edge)
			if err != nil {
				return err
			}
			llvmBlock := frame.blocks[block.Preds[i]]
			phi.llvm.AddIncoming([]llvm.Value{llvmVal}, []llvm.BasicBlock{llvmBlock})
		}
	}

	return nil
}

func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) error {
	switch instr := instr.(type) {
	case ssa.Value:
		value, err := c.parseExpr(frame, instr)
		frame.locals[instr] = value
		return err
	case *ssa.If:
		cond, err := c.parseExpr(frame, instr.Cond)
		if err != nil {
			return err
		}
		block := instr.Block()
		blockThen := frame.blocks[block.Succs[0]]
		blockElse := frame.blocks[block.Succs[1]]
		c.builder.CreateCondBr(cond, blockThen, blockElse)
		return nil
	case *ssa.Jump:
		blockJump := frame.blocks[instr.Block().Succs[0]]
		c.builder.CreateBr(blockJump)
		return nil
	case *ssa.Panic:
		value, err := c.parseExpr(frame, instr.X)
		if err != nil {
			return err
		}
		c.builder.CreateCall(c.mod.NamedFunction("runtime._panic"), []llvm.Value{value}, "")
		c.builder.CreateUnreachable()
		return nil
	case *ssa.Return:
		if len(instr.Results) == 0 {
			c.builder.CreateRetVoid()
			return nil
		} else if len(instr.Results) == 1 {
			val, err := c.parseExpr(frame, instr.Results[0])
			if err != nil {
				return err
			}
			c.builder.CreateRet(val)
			return nil
		} else {
			return errors.New("todo: return value")
		}
	case *ssa.Store:
		addr, err := c.parseExpr(frame, instr.Addr)
		if err != nil {
			return err
		}
		val, err := c.parseExpr(frame, instr.Val)
		if err != nil {
			return err
		}
		c.builder.CreateStore(val, addr)
		return nil
	default:
		return errors.New("unknown instruction: " + fmt.Sprintf("%#v", instr))
	}
}

func (c *Compiler) parseBuiltin(frame *Frame, args []ssa.Value, callName string) (llvm.Value, error) {
	fmt.Printf("    builtin: %v\n", callName)

	switch callName {
	case "print", "println":
		for i, arg := range args {
			if i >= 1 {
				c.builder.CreateCall(c.mod.NamedFunction("runtime.printspace"), nil, "")
			}
			fmt.Printf("    arg: %s\n", arg);
			value, err := c.parseExpr(frame, arg)
			if err != nil {
				return llvm.Value{}, err
			}
			typ := arg.Type()
			if _, ok := typ.(*types.Named); ok {
				typ = typ.Underlying()
			}
			switch typ := typ.(type) {
			case *types.Basic:
				switch typ.Kind() {
				case types.Uint8:
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printbyte"), []llvm.Value{value}, "")
				case types.Int, types.Int32: // TODO: assumes a 32-bit int type
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printint32"), []llvm.Value{value}, "")
				case types.Uint, types.Uint32:
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printuint32"), []llvm.Value{value}, "")
				case types.Int64:
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printint64"), []llvm.Value{value}, "")
				case types.Uint64:
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printuint64"), []llvm.Value{value}, "")
				case types.String:
					c.builder.CreateCall(c.mod.NamedFunction("runtime.printstring"), []llvm.Value{value}, "")
				default:
					return llvm.Value{}, errors.New("unknown basic arg type: " + fmt.Sprintf("%#v", typ))
				}
			default:
				return llvm.Value{}, errors.New("unknown arg type: " + fmt.Sprintf("%#v", typ))
			}
		}
		if callName == "println" {
			c.builder.CreateCall(c.mod.NamedFunction("runtime.printnl"), nil, "")
		}
		return llvm.Value{}, nil // print() or println() returns void
	case "len":
		value, err := c.parseExpr(frame, args[0])
		if err != nil {
			return llvm.Value{}, err
		}
		switch typ := args[0].Type().(type) {
		case *types.Basic:
			switch typ.Kind() {
			case types.String:
				return c.builder.CreateExtractValue(value, 0, "len"), nil
			default:
				return llvm.Value{}, errors.New("todo: len: unknown basic type")
			}
		default:
			return llvm.Value{}, errors.New("todo: len: unknown type")
		}
	default:
		return llvm.Value{}, errors.New("todo: builtin: " + callName)
	}
}

func (c *Compiler) parseFunctionCall(frame *Frame, call *ssa.CallCommon, fn *ssa.Function) (llvm.Value, error) {
	fmt.Printf("    function: %s\n", fn)

	name := c.getFunctionName(fn)
	target := c.mod.NamedFunction(name)
	if target.IsNil() {
		return llvm.Value{}, errors.New("undefined function: " + name)
	}

	var params []llvm.Value
	for _, param := range call.Args {
		val, err := c.parseExpr(frame, param)
		if err != nil {
			return llvm.Value{}, err
		}
		params = append(params, val)
	}

	return c.builder.CreateCall(target, params, ""), nil
}

func (c *Compiler) parseCall(frame *Frame, instr *ssa.Call) (llvm.Value, error) {
	fmt.Printf("    call: %s\n", instr)

	switch call := instr.Common().Value.(type) {
	case *ssa.Builtin:
		return c.parseBuiltin(frame, instr.Common().Args, call.Name())
	case *ssa.Function:
		return c.parseFunctionCall(frame, instr.Common(), call)
	default:
		return llvm.Value{}, errors.New("todo: unknown call type: " + fmt.Sprintf("%#v", call))
	}
}

func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
	fmt.Printf("      expr: %v\n", expr)

	if frame != nil {
		if value, ok := frame.locals[expr]; ok {
			// Value is a local variable that has already been computed.
			fmt.Println("        from local var")
			if value.IsNil() {
				return llvm.Value{}, errors.New("undefined local var (from cgo?)")
			}
			return value, nil
		}
	}

	switch expr := expr.(type) {
	case *ssa.Alloc:
		typ, err := c.getLLVMType(expr.Type().Underlying().(*types.Pointer).Elem())
		if err != nil {
			return llvm.Value{}, err
		}
		var buf llvm.Value
		if expr.Heap {
			// TODO: escape analysis
			buf = c.builder.CreateMalloc(typ, expr.Comment)
		} else {
			buf = c.builder.CreateAlloca(typ, expr.Comment)
		}
		if err != nil {
			return llvm.Value{}, err
		}
		zero, err := c.getZeroValue(typ)
		if err != nil {
			return llvm.Value{}, err
		}
		c.builder.CreateStore(zero, buf) // zero-initialize var
		return buf, nil
	case *ssa.BinOp:
		return c.parseBinOp(frame, expr)
	case *ssa.Call:
		return c.parseCall(frame, expr)
	case *ssa.ChangeType:
		return c.parseConvert(frame, expr.Type(), expr.X)
	case *ssa.Const:
		return c.parseConst(expr)
	case *ssa.Convert:
		return c.parseConvert(frame, expr.Type(), expr.X)
	case *ssa.Extract:
		value, err := c.parseExpr(frame, expr.Tuple)
		if err != nil {
			return llvm.Value{}, err
		}
		result := c.builder.CreateExtractValue(value, expr.Index, "")
		return result, nil
	case *ssa.FieldAddr:
		val, err := c.parseExpr(frame, expr.X)
		if err != nil {
			return llvm.Value{}, err
		}
		indices := []llvm.Value{
			llvm.ConstInt(llvm.Int32Type(), 0, false),
			llvm.ConstInt(llvm.Int32Type(), uint64(expr.Field), false),
		}
		return c.builder.CreateGEP(val, indices, ""), nil
	case *ssa.Global:
		fullName := pkgPrefix(expr.Pkg) + "." + expr.Name()
		value := c.mod.NamedGlobal(fullName)
		if value.IsNil() {
			return llvm.Value{}, errors.New("global not found: " + fullName)
		}
		return value, nil
	case *ssa.IndexAddr:
		val, err := c.parseExpr(frame, expr.X)
		if err != nil {
			return llvm.Value{}, err
		}
		index, err := c.parseExpr(frame, expr.Index)
		if err != nil {
			return llvm.Value{}, err
		}

		// Get buffer length
		var buflen llvm.Value
		typ := expr.X.Type().(*types.Pointer).Elem()
		switch typ := typ.(type) {
		case *types.Array:
			buflen = llvm.ConstInt(llvm.Int32Type(), uint64(typ.Len()), false)
		default:
			return llvm.Value{}, errors.New("todo: indexaddr: len")
		}

		// Bounds check
		// TODO: inline, and avoid if possible
		constZero := llvm.ConstInt(c.intType, 0, false)
		isNegative := c.builder.CreateICmp(llvm.IntSLT, index, constZero, "") // index < 0
		isTooBig := c.builder.CreateICmp(llvm.IntSGE, index, buflen, "") // index >= len(value)
		isOverflow := c.builder.CreateOr(isNegative, isTooBig, "")
		c.builder.CreateCall(c.mod.NamedFunction("runtime.boundsCheck"), []llvm.Value{isOverflow}, "")

		indices := []llvm.Value{
			llvm.ConstInt(llvm.Int32Type(), 0, false),
			index,
		}
		return c.builder.CreateGEP(val, indices, ""), nil
	case *ssa.Lookup:
		if expr.CommaOk {
			return llvm.Value{}, errors.New("todo: lookup with comma-ok")
		}
		if _, ok := expr.X.Type().(*types.Map); ok {
			return llvm.Value{}, errors.New("todo: lookup in map")
		}
		// Value type must be a string, which is a basic type.
		if expr.X.Type().(*types.Basic).Kind() != types.String {
			panic("lookup on non-string?")
		}
		value, err := c.parseExpr(frame, expr.X)
		if err != nil {
			return llvm.Value{}, nil
		}
		index, err := c.parseExpr(frame, expr.Index)
		if err != nil {
			return llvm.Value{}, nil
		}

		// Bounds check
		// TODO: inline, and avoid if possible
		if frame.llvmFn.Name() != "runtime.boundsCheck" {
			constZero := llvm.ConstInt(c.intType, 0, false)
			isNegative := c.builder.CreateICmp(llvm.IntSLT, index, constZero, "") // index < 0
			strlen, err := c.parseBuiltin(frame, []ssa.Value{expr.X}, "len")
			if err != nil {
				return llvm.Value{}, err // shouldn't happen
			}
			isTooBig := c.builder.CreateICmp(llvm.IntSGE, index, strlen, "") // index >= len(value)
			isOverflow := c.builder.CreateOr(isNegative, isTooBig, "")
			c.builder.CreateCall(c.mod.NamedFunction("runtime.boundsCheck"), []llvm.Value{isOverflow}, "")
		}

		// Lookup byte
		buf := c.builder.CreateExtractValue(value, 1, "")
		bufPtr := c.builder.CreateGEP(buf, []llvm.Value{index}, "")
		return c.builder.CreateLoad(bufPtr, ""), nil
	case *ssa.MakeInterface:
		val, err := c.parseExpr(frame, expr.X)
		if err != nil {
			return llvm.Value{}, err
		}
		var itfValue llvm.Value
		switch typ := expr.X.Type().(type) {
		case *types.Basic:
			itfValueType := llvm.PointerType(llvm.Int8Type(), 0)
			if typ.Info() & types.IsInteger != 0 { // TODO: 64-bit int on 32-bit platform
				itfValue = c.builder.CreateIntToPtr(val, itfValueType, "")
			} else if typ.Kind() == types.String {
				// TODO: escape analysis
				itfValue = c.builder.CreateMalloc(c.stringType, "")
				c.builder.CreateStore(val, itfValue)
				itfValue = c.builder.CreateBitCast(itfValue, itfValueType, "")
			} else {
				return llvm.Value{}, errors.New("todo: make interface: unknown basic type")
			}
		default:
			return llvm.Value{}, errors.New("todo: make interface: unknown type")
		}
		itfType := c.getInterfaceType(expr.X.Type())
		itf := c.ctx.ConstStruct([]llvm.Value{itfType, llvm.Undef(llvm.PointerType(llvm.Int8Type(), 0))}, false)
		itf = c.builder.CreateInsertValue(itf, itfValue, 1, "")
		return itf, nil
	case *ssa.Phi:
		t, err := c.getLLVMType(expr.Type())
		if err != nil {
			return llvm.Value{}, err
		}
		phi := c.builder.CreatePHI(t, "")
		frame.phis = append(frame.phis, Phi{expr, phi})
		return phi, nil
	case *ssa.TypeAssert:
		if !expr.CommaOk {
			return llvm.Value{}, errors.New("todo: type assert without comma-ok")
		}
		itf, err := c.parseExpr(frame, expr.X)
		if err != nil {
			return llvm.Value{}, err
		}
		assertedType, err := c.getLLVMType(expr.AssertedType)
		if err != nil {
			return llvm.Value{}, err
		}
		assertedTypeNum := c.getInterfaceType(expr.AssertedType)
		actualTypeNum := c.builder.CreateExtractValue(itf, 0, "interface.type")
		valuePtr := c.builder.CreateExtractValue(itf, 1, "interface.value")
		var value llvm.Value
		switch typ := expr.AssertedType.(type) {
		case *types.Basic:
			if typ.Info() & types.IsInteger != 0 {
				value = c.builder.CreatePtrToInt(valuePtr, assertedType, "")
			} else if typ.Kind() == types.String {
				valueStringPtr := c.builder.CreateBitCast(valuePtr, llvm.PointerType(c.stringType, 0), "")
				value = c.builder.CreateLoad(valueStringPtr, "")
			} else {
				return llvm.Value{}, errors.New("todo: typeassert: unknown basic type")
			}
		default:
			return llvm.Value{}, errors.New("todo: typeassert: unknown type")
		}
		commaOk := c.builder.CreateICmp(llvm.IntEQ, assertedTypeNum, actualTypeNum, "")
		tuple := llvm.ConstStruct([]llvm.Value{llvm.Undef(assertedType), llvm.Undef(llvm.Int1Type())}, false) // create empty tuple
		tuple = c.builder.CreateInsertValue(tuple, value, 0, "") // insert value
		tuple = c.builder.CreateInsertValue(tuple, commaOk, 1, "") // insert 'comma ok' boolean
		return tuple, nil
	case *ssa.UnOp:
		return c.parseUnOp(frame, expr)
	default:
		return llvm.Value{}, errors.New("todo: unknown expression: " + fmt.Sprintf("%#v", expr))
	}
}

func (c *Compiler) parseBinOp(frame *Frame, binop *ssa.BinOp) (llvm.Value, error) {
	x, err := c.parseExpr(frame, binop.X)
	if err != nil {
		return llvm.Value{}, err
	}
	y, err := c.parseExpr(frame, binop.Y)
	if err != nil {
		return llvm.Value{}, err
	}
	typ := binop.X.Type()
	if typNamed, ok := typ.(*types.Named); ok {
		typ = typNamed.Underlying()
	}
	signed := typ.(*types.Basic).Info() & types.IsUnsigned == 0
	switch binop.Op {
	case token.ADD: // +
		return c.builder.CreateAdd(x, y, ""), nil
	case token.SUB: // -
		return c.builder.CreateSub(x, y, ""), nil
	case token.MUL: // *
		return c.builder.CreateMul(x, y, ""), nil
	case token.QUO: // /
		if signed {
			return c.builder.CreateSDiv(x, y, ""), nil
		} else {
			return c.builder.CreateUDiv(x, y, ""), nil
		}
	case token.REM: // %
		if signed {
			return c.builder.CreateSRem(x, y, ""), nil
		} else {
			return c.builder.CreateURem(x, y, ""), nil
		}
	case token.AND: // &
		return c.builder.CreateAnd(x, y, ""), nil
	case token.OR:  // |
		return c.builder.CreateOr(x, y, ""), nil
	case token.XOR: // ^
		return c.builder.CreateXor(x, y, ""), nil
	case token.SHL: // <<
		return c.builder.CreateShl(x, y, ""), nil
	case token.SHR: // >>
		if signed {
			return c.builder.CreateAShr(x, y, ""), nil
		} else {
			return c.builder.CreateLShr(x, y, ""), nil
		}
	case token.AND_NOT: // &^
		// Go specific. Calculate "and not" with x & (~y)
		inv := c.builder.CreateNot(y, "") // ~y
		return c.builder.CreateAnd(x, inv, ""), nil
	case token.EQL: // ==
		return c.builder.CreateICmp(llvm.IntEQ, x, y, ""), nil
	case token.NEQ: // !=
		return c.builder.CreateICmp(llvm.IntNE, x, y, ""), nil
	case token.LSS: // <
		if signed {
			return c.builder.CreateICmp(llvm.IntSLT, x, y, ""), nil
		} else {
			return c.builder.CreateICmp(llvm.IntULT, x, y, ""), nil
		}
	case token.LEQ: // <=
		if signed {
			return c.builder.CreateICmp(llvm.IntSLE, x, y, ""), nil
		} else {
			return c.builder.CreateICmp(llvm.IntULE, x, y, ""), nil
		}
	case token.GTR: // >
		if signed {
			return c.builder.CreateICmp(llvm.IntSGT, x, y, ""), nil
		} else {
			return c.builder.CreateICmp(llvm.IntUGT, x, y, ""), nil
		}
	case token.GEQ: // >=
		if signed {
			return c.builder.CreateICmp(llvm.IntSGE, x, y, ""), nil
		} else {
			return c.builder.CreateICmp(llvm.IntUGE, x, y, ""), nil
		}
	default:
		return llvm.Value{}, errors.New("unknown binop")
	}
}

func (c *Compiler) parseConst(expr *ssa.Const) (llvm.Value, error) {
	switch expr.Value.Kind() {
	case constant.Bool, constant.Int:
		return c.parseConstInt(expr, expr.Type())
	case constant.String:
		str := constant.StringVal(expr.Value)
		strLen := llvm.ConstInt(c.stringLenType, uint64(len(str)), false)
		strPtr := c.builder.CreateGlobalStringPtr(str, ".str") // TODO: remove \0 at end
		strObj := llvm.ConstStruct([]llvm.Value{strLen, strPtr}, false)
		return strObj, nil
	default:
		return llvm.Value{}, errors.New("todo: unknown constant: " + fmt.Sprintf("%#v", expr.Value.Kind()))
	}
}

func (c *Compiler) parseConstInt(expr *ssa.Const, typ types.Type) (llvm.Value, error) {
	switch typ := typ.(type) {
	case *types.Basic:
		llvmType, err := c.getLLVMType(typ)
		if err != nil {
			return llvm.Value{}, err
		}
		if typ.Info() & types.IsBoolean != 0 {
			b := constant.BoolVal(expr.Value)
			n := uint64(0)
			if b {
				n = 1
			}
			return llvm.ConstInt(llvmType, n, false), nil
		} else if typ.Info() & types.IsUnsigned != 0 {
			n, _ := constant.Uint64Val(expr.Value)
			return llvm.ConstInt(llvmType, n, false), nil
		} else if typ.Info() & types.IsInteger != 0 { // signed
			n, _ := constant.Int64Val(expr.Value)
			return llvm.ConstInt(llvmType, uint64(n), true), nil
		} else {
			return llvm.Value{}, errors.New("unknown integer constant")
		}
	case *types.Named:
		return c.parseConstInt(expr, typ.Underlying())
	default:
		return llvm.Value{}, errors.New("todo: unknown constant: " + fmt.Sprintf("%#v", typ))
	}
}

func (c *Compiler) parseConvert(frame *Frame, typeTo types.Type, x ssa.Value) (llvm.Value, error) {
	switch typeTo := typeTo.(type) {
	case *types.Basic:
		value, err := c.parseExpr(frame, x)
		if err != nil {
			return value, nil
		}

		llvmTypeFrom, err := c.getLLVMType(x.Type())
		if err != nil {
			return llvm.Value{}, err
		}
		sizeFrom := c.targetData.TypeAllocSize(llvmTypeFrom)
		llvmTypeTo, err := c.getLLVMType(typeTo)
		if err != nil {
			return llvm.Value{}, err
		}
		sizeTo := c.targetData.TypeAllocSize(llvmTypeTo)

		if sizeFrom == sizeTo {
			return c.builder.CreateBitCast(value, llvmTypeTo, ""), nil
		}

		if typeTo.Info() & types.IsInteger == 0 { // if not integer
			return llvm.Value{}, errors.New("todo: convert: extend non-integer type")
		}

		if sizeFrom > sizeTo {
			return c.builder.CreateTrunc(value, llvmTypeTo, ""), nil
		} else if typeTo.Info() & types.IsUnsigned != 0 { // if unsigned
			return c.builder.CreateZExt(value, llvmTypeTo, ""), nil
		} else { // if signed
			return c.builder.CreateSExt(value, llvmTypeTo, ""), nil
		}
	case *types.Named:
		return c.parseConvert(frame, typeTo.Underlying(), x)
	default:
		return llvm.Value{}, errors.New("todo: convert: extend non-basic type: " + fmt.Sprintf("%#v", typeTo))
	}
}

func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
	x, err := c.parseExpr(frame, unop.X)
	if err != nil {
		return llvm.Value{}, err
	}
	switch unop.Op {
	case token.NOT: // !
		return c.builder.CreateNot(x, ""), nil
	case token.SUB: // -num
		return c.builder.CreateSub(llvm.ConstInt(x.Type(), 0, false), x, ""), nil
	case token.MUL: // *ptr, dereference pointer
		return c.builder.CreateLoad(x, ""), nil
	default:
		return llvm.Value{}, errors.New("todo: unknown unop")
	}
}

// IR returns the whole IR as a human-readable string.
func (c *Compiler) IR() string {
	return c.mod.String()
}

func (c *Compiler) Verify() error {
	return llvm.VerifyModule(c.mod, 0)
}

func (c *Compiler) LinkModule(mod llvm.Module) error {
	return llvm.LinkModules(c.mod, mod)
}

func (c *Compiler) ApplyFunctionSections() {
	// Put every function in a separate section. This makes it possible for the
	// linker to remove dead code (--gc-sections).
	llvmFn := c.mod.FirstFunction()
	for !llvmFn.IsNil() {
		if !llvmFn.IsDeclaration() {
			llvmFn.SetSection(".text." + llvmFn.Name())
		}
		llvmFn = llvm.NextFunction(llvmFn)
	}
}

func (c *Compiler) Optimize(optLevel, sizeLevel int) {
	builder := llvm.NewPassManagerBuilder()
	defer builder.Dispose()
	builder.SetOptLevel(optLevel)
	builder.SetSizeLevel(sizeLevel)
	builder.UseInlinerWithThreshold(200) // TODO depend on opt level, and -Os

	funcPasses := llvm.NewFunctionPassManagerForModule(c.mod)
	defer funcPasses.Dispose()
	builder.PopulateFunc(funcPasses)

	modPasses := llvm.NewPassManager()
	defer modPasses.Dispose()
	builder.Populate(modPasses)

	modPasses.Run(c.mod)
}

func (c *Compiler) EmitObject(path string) error {
	// Generate output
	var buf []byte
	if strings.HasSuffix(path, ".o") {
		llvmBuf, err := c.machine.EmitToMemoryBuffer(c.mod, llvm.ObjectFile)
		if err != nil {
			return err
		}
		buf = llvmBuf.Bytes()
	} else if strings.HasSuffix(path, ".bc") {
		buf = llvm.WriteBitcodeToMemoryBuffer(c.mod).Bytes()
	} else if strings.HasSuffix(path, ".ll") {
		buf = []byte(c.mod.String())
	} else {
		return errors.New("unknown output file extension")
	}

	// Write output to file
	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
	if err != nil {
		return err
	}
	f.Write(buf)
	f.Close()
	return nil
}

// Helper function for Compiler object.
func Compile(pkgName, runtimePath, outpath, target string, printIR bool) error {
	var buildTags []string
	// TODO: put this somewhere else
	if target == "pca10040" {
		buildTags = append(buildTags, "nrf")
		target = "armv7m-none-eabi"
	}

	c, err := NewCompiler(pkgName, target)
	if err != nil {
		return err
	}

	parseErr := c.Parse(pkgName, buildTags)
	if printIR {
		fmt.Println(c.IR())
	}
	if parseErr != nil {
		return parseErr
	}

	// Add C runtime.
	runtime, err := llvm.ParseBitcodeFile(runtimePath)
	if err != nil {
		return err
	}
	err = c.LinkModule(runtime)
	if err != nil {
		return err
	}

	c.ApplyFunctionSections() // -ffunction-sections

	if err := c.Verify(); err != nil {
		return err
	}
	c.Optimize(2, 1) // -O2 -Os
	if err := c.Verify(); err != nil {
		return err
	}

	err = c.EmitObject(outpath)
	if err != nil {
		return err
	}

	return nil
}


func main() {
	outpath := flag.String("o", "", "output filename")
	printIR := flag.Bool("printir", false, "print LLVM IR after optimizing")
	runtime := flag.String("runtime", "", "runtime LLVM bitcode files (from C sources)")
	target := flag.String("target", llvm.DefaultTargetTriple(), "LLVM target")

	flag.Parse()

	if *outpath == "" || flag.NArg() != 1 {
		fmt.Fprintf(os.Stderr, "usage: %s [-printir] -runtime=<runtime.bc> [-target=<target>] -o <output> <input>", os.Args[0])
		flag.PrintDefaults()
		return
	}

	os.Setenv("CC", "clang -target=" + *target)

	err := Compile(flag.Args()[0], *runtime, *outpath, *target, *printIR)
	if err != nil {
		fmt.Fprintln(os.Stderr, "error:", err)
		os.Exit(1)
	}
}