writer.go

	// least.

	pragma := asPragmaFlag(decl.Pragma)
	if pragma&ir.Systemstack != 0 && pragma&ir.Nosplit != 0 {
		w.p.errorf(decl, "go:nosplit and go:systemstack cannot be combined")
	}
	wi := asWasmImport(decl.Pragma)

	if decl.Body != nil {
		if pragma&ir.Noescape != 0 {
			w.p.errorf(decl, "can only use //go:noescape with external func implementations")
		}
		if wi != nil {
			w.p.errorf(decl, "can only use //go:wasmimport with external func implementations")
		}
		if (pragma&ir.UintptrKeepAlive != 0 && pragma&ir.UintptrEscapes == 0) && pragma&ir.Nosplit == 0 {
			// Stack growth can't handle uintptr arguments that may
			// be pointers (as we don't know which are pointers
			// when creating the stack map). Thus uintptrkeepalive
			// functions (and all transitive callees) must be
			// nosplit.
			//
			// N.B. uintptrescapes implies uintptrkeepalive but it
			// is OK since the arguments must escape to the heap.
			//
			// TODO(prattmic): Add recursive nosplit check of callees.
			// TODO(prattmic): Functions with no body (i.e.,
			// assembly) must also be nosplit, but we can't check
			// that here.
			w.p.errorf(decl, "go:uintptrkeepalive requires go:nosplit")
		}
	} else {
		if base.Flag.Complete || decl.Name.Value == "init" {
			// Linknamed functions are allowed to have no body. Hopefully
			// the linkname target has a body. See issue 23311.
			// Wasmimport functions are also allowed to have no body.
			if _, ok := w.p.linknames[obj]; !ok && wi == nil {
				w.p.errorf(decl, "missing function body")
			}
		}
	}

	sig, block := obj.Type().(*types2.Signature), decl.Body
	body, closureVars := w.p.bodyIdx(sig, block, w.dict)
	assert(len(closureVars) == 0)

	w.Sync(pkgbits.SyncFuncExt)
	w.pragmaFlag(pragma)
	w.linkname(obj)

	if buildcfg.GOARCH == "wasm" {
		if wi != nil {
			w.String(wi.Module)
			w.String(wi.Name)
		} else {
			w.String("")
			w.String("")
		}
	}

	w.Bool(false) // stub extension
	w.Reloc(pkgbits.RelocBody, body)
	w.Sync(pkgbits.SyncEOF)
}

func (w *writer) typeExt(obj *types2.TypeName) {
	decl, ok := w.p.typDecls[obj]
	assert(ok)

	w.Sync(pkgbits.SyncTypeExt)

	w.pragmaFlag(asPragmaFlag(decl.Pragma))

	// No LSym.SymIdx info yet.
	w.Int64(-1)
	w.Int64(-1)
}

func (w *writer) varExt(obj *types2.Var) {
	w.Sync(pkgbits.SyncVarExt)
	w.linkname(obj)
}

func (w *writer) linkname(obj types2.Object) {
	w.Sync(pkgbits.SyncLinkname)
	w.Int64(-1)
	w.String(w.p.linknames[obj])
}

func (w *writer) pragmaFlag(p ir.PragmaFlag) {
	w.Sync(pkgbits.SyncPragma)
	w.Int(int(p))
}

// @@@ Function bodies

// bodyIdx returns the index for the given function body (specified by
// block), adding it to the export data
func (pw *pkgWriter) bodyIdx(sig *types2.Signature, block *syntax.BlockStmt, dict *writerDict) (idx pkgbits.Index, closureVars []posVar) {
	w := pw.newWriter(pkgbits.RelocBody, pkgbits.SyncFuncBody)
	w.sig = sig
	w.dict = dict

	w.funcargs(sig)
	if w.Bool(block != nil) {
		w.stmts(block.List)
		w.pos(block.Rbrace)
	}

	return w.Flush(), w.closureVars
}

func (w *writer) funcargs(sig *types2.Signature) {
	do := func(params *types2.Tuple, result bool) {
		for i := 0; i < params.Len(); i++ {
			w.funcarg(params.At(i), result)
		}
	}

	if recv := sig.Recv(); recv != nil {
		w.funcarg(recv, false)
	}
	do(sig.Params(), false)
	do(sig.Results(), true)
}

func (w *writer) funcarg(param *types2.Var, result bool) {
	if param.Name() != "" || result {
		w.addLocal(param)
	}
}

// addLocal records the declaration of a new local variable.
func (w *writer) addLocal(obj *types2.Var) {
	idx := len(w.localsIdx)

	w.Sync(pkgbits.SyncAddLocal)
	if w.p.SyncMarkers() {
		w.Int(idx)
	}
	w.varDictIndex(obj)

	if w.localsIdx == nil {
		w.localsIdx = make(map[*types2.Var]int)
	}
	w.localsIdx[obj] = idx
}

// useLocal writes a reference to the given local or free variable
// into the bitstream.
func (w *writer) useLocal(pos syntax.Pos, obj *types2.Var) {
	w.Sync(pkgbits.SyncUseObjLocal)

	if idx, ok := w.localsIdx[obj]; w.Bool(ok) {
		w.Len(idx)
		return
	}

	idx, ok := w.closureVarsIdx[obj]
	if !ok {
		if w.closureVarsIdx == nil {
			w.closureVarsIdx = make(map[*types2.Var]int)
		}
		idx = len(w.closureVars)
		w.closureVars = append(w.closureVars, posVar{pos, obj})
		w.closureVarsIdx[obj] = idx
	}
	w.Len(idx)
}

func (w *writer) openScope(pos syntax.Pos) {
	w.Sync(pkgbits.SyncOpenScope)
	w.pos(pos)
}

func (w *writer) closeScope(pos syntax.Pos) {
	w.Sync(pkgbits.SyncCloseScope)
	w.pos(pos)
	w.closeAnotherScope()
}

func (w *writer) closeAnotherScope() {
	w.Sync(pkgbits.SyncCloseAnotherScope)
}

// @@@ Statements

// stmt writes the given statement into the function body bitstream.
func (w *writer) stmt(stmt syntax.Stmt) {
	var stmts []syntax.Stmt
	if stmt != nil {
		stmts = []syntax.Stmt{stmt}
	}
	w.stmts(stmts)
}

func (w *writer) stmts(stmts []syntax.Stmt) {
	w.Sync(pkgbits.SyncStmts)
	for _, stmt := range stmts {
		w.stmt1(stmt)
	}
	w.Code(stmtEnd)
	w.Sync(pkgbits.SyncStmtsEnd)
}

func (w *writer) stmt1(stmt syntax.Stmt) {
	switch stmt := stmt.(type) {
	default:
		w.p.unexpected("statement", stmt)

	case nil, *syntax.EmptyStmt:
		return

	case *syntax.AssignStmt:
		switch {
		case stmt.Rhs == nil:
			w.Code(stmtIncDec)
			w.op(binOps[stmt.Op])
			w.expr(stmt.Lhs)
			w.pos(stmt)

		case stmt.Op != 0 && stmt.Op != syntax.Def:
			w.Code(stmtAssignOp)
			w.op(binOps[stmt.Op])
			w.expr(stmt.Lhs)
			w.pos(stmt)

			var typ types2.Type
			if stmt.Op != syntax.Shl && stmt.Op != syntax.Shr {
				typ = w.p.typeOf(stmt.Lhs)
			}
			w.implicitConvExpr(typ, stmt.Rhs)

		default:
			w.assignStmt(stmt, stmt.Lhs, stmt.Rhs)
		}

	case *syntax.BlockStmt:
		w.Code(stmtBlock)
		w.blockStmt(stmt)

	case *syntax.BranchStmt:
		w.Code(stmtBranch)
		w.pos(stmt)
		w.op(branchOps[stmt.Tok])
		w.optLabel(stmt.Label)

	case *syntax.CallStmt:
		w.Code(stmtCall)
		w.pos(stmt)
		w.op(callOps[stmt.Tok])
		w.expr(stmt.Call)

	case *syntax.DeclStmt:
		for _, decl := range stmt.DeclList {
			w.declStmt(decl)
		}

	case *syntax.ExprStmt:
		w.Code(stmtExpr)
		w.expr(stmt.X)

	case *syntax.ForStmt:
		w.Code(stmtFor)
		w.forStmt(stmt)

	case *syntax.IfStmt:
		w.Code(stmtIf)
		w.ifStmt(stmt)

	case *syntax.LabeledStmt:
		w.Code(stmtLabel)
		w.pos(stmt)
		w.label(stmt.Label)
		w.stmt1(stmt.Stmt)

	case *syntax.ReturnStmt:
		w.Code(stmtReturn)
		w.pos(stmt)

		resultTypes := w.sig.Results()
		dstType := func(i int) types2.Type {
			return resultTypes.At(i).Type()
		}
		w.multiExpr(stmt, dstType, unpackListExpr(stmt.Results))

	case *syntax.SelectStmt:
		w.Code(stmtSelect)
		w.selectStmt(stmt)

	case *syntax.SendStmt:
		chanType := types2.CoreType(w.p.typeOf(stmt.Chan)).(*types2.Chan)

		w.Code(stmtSend)
		w.pos(stmt)
		w.expr(stmt.Chan)
		w.implicitConvExpr(chanType.Elem(), stmt.Value)

	case *syntax.SwitchStmt:
		w.Code(stmtSwitch)
		w.switchStmt(stmt)
	}
}

func (w *writer) assignList(expr syntax.Expr) {
	exprs := unpackListExpr(expr)
	w.Len(len(exprs))

	for _, expr := range exprs {
		w.assign(expr)
	}
}

func (w *writer) assign(expr syntax.Expr) {
	expr = unparen(expr)

	if name, ok := expr.(*syntax.Name); ok {
		if name.Value == "_" {
			w.Code(assignBlank)
			return
		}

		if obj, ok := w.p.info.Defs[name]; ok {
			obj := obj.(*types2.Var)

			w.Code(assignDef)
			w.pos(obj)
			w.localIdent(obj)
			w.typ(obj.Type())

			// TODO(mdempsky): Minimize locals index size by deferring
			// this until the variables actually come into scope.
			w.addLocal(obj)
			return
		}
	}

	w.Code(assignExpr)
	w.expr(expr)
}

func (w *writer) declStmt(decl syntax.Decl) {
	switch decl := decl.(type) {
	default:
		w.p.unexpected("declaration", decl)

	case *syntax.ConstDecl, *syntax.TypeDecl:

	case *syntax.VarDecl:
		w.assignStmt(decl, namesAsExpr(decl.NameList), decl.Values)
	}
}

// assignStmt writes out an assignment for "lhs = rhs".
func (w *writer) assignStmt(pos poser, lhs0, rhs0 syntax.Expr) {
	lhs := unpackListExpr(lhs0)
	rhs := unpackListExpr(rhs0)

	w.Code(stmtAssign)
	w.pos(pos)

	// As if w.assignList(lhs0).
	w.Len(len(lhs))
	for _, expr := range lhs {
		w.assign(expr)
	}

	dstType := func(i int) types2.Type {
		dst := lhs[i]

		// Finding dstType is somewhat involved, because for VarDecl
		// statements, the Names are only added to the info.{Defs,Uses}
		// maps, not to info.Types.
		if name, ok := unparen(dst).(*syntax.Name); ok {
			if name.Value == "_" {
				return nil // ok: no implicit conversion
			} else if def, ok := w.p.info.Defs[name].(*types2.Var); ok {
				return def.Type()
			} else if use, ok := w.p.info.Uses[name].(*types2.Var); ok {
				return use.Type()
			} else {
				w.p.fatalf(dst, "cannot find type of destination object: %v", dst)
			}
		}

		return w.p.typeOf(dst)
	}

	w.multiExpr(pos, dstType, rhs)
}

func (w *writer) blockStmt(stmt *syntax.BlockStmt) {
	w.Sync(pkgbits.SyncBlockStmt)
	w.openScope(stmt.Pos())
	w.stmts(stmt.List)
	w.closeScope(stmt.Rbrace)
}

func (w *writer) forStmt(stmt *syntax.ForStmt) {
	w.Sync(pkgbits.SyncForStmt)
	w.openScope(stmt.Pos())

	if rang, ok := stmt.Init.(*syntax.RangeClause); w.Bool(ok) {
		w.pos(rang)
		w.assignList(rang.Lhs)
		w.expr(rang.X)

		xtyp := w.p.typeOf(rang.X)
		if _, isMap := types2.CoreType(xtyp).(*types2.Map); isMap {
			w.rtype(xtyp)
		}
		{
			lhs := unpackListExpr(rang.Lhs)
			assign := func(i int, src types2.Type) {
				if i >= len(lhs) {
					return
				}
				dst := unparen(lhs[i])
				if name, ok := dst.(*syntax.Name); ok && name.Value == "_" {
					return
				}

				var dstType types2.Type
				if rang.Def {
					// For `:=` assignments, the LHS names only appear in Defs,
					// not Types (as used by typeOf).
					dstType = w.p.info.Defs[dst.(*syntax.Name)].(*types2.Var).Type()
				} else {
					dstType = w.p.typeOf(dst)
				}

				w.convRTTI(src, dstType)
			}

			keyType, valueType := w.p.rangeTypes(rang.X)
			assign(0, keyType)
			assign(1, valueType)
		}

	} else {
		w.pos(stmt)
		w.stmt(stmt.Init)
		w.optExpr(stmt.Cond)
		w.stmt(stmt.Post)
	}

	w.blockStmt(stmt.Body)
	w.Bool(base.Debug.LoopVar > 0)
	w.closeAnotherScope()
}

// rangeTypes returns the types of values produced by ranging over
// expr.
func (pw *pkgWriter) rangeTypes(expr syntax.Expr) (key, value types2.Type) {
	typ := pw.typeOf(expr)
	switch typ := types2.CoreType(typ).(type) {
	case *types2.Pointer: // must be pointer to array
		return types2.Typ[types2.Int], types2.CoreType(typ.Elem()).(*types2.Array).Elem()
	case *types2.Array:
		return types2.Typ[types2.Int], typ.Elem()
	case *types2.Slice:
		return types2.Typ[types2.Int], typ.Elem()
	case *types2.Basic:
		if typ.Info()&types2.IsString != 0 {
			return types2.Typ[types2.Int], runeTypeName.Type()
		}
	case *types2.Map:
		return typ.Key(), typ.Elem()
	case *types2.Chan:
		return typ.Elem(), nil
	}
	pw.fatalf(expr, "unexpected range type: %v", typ)
	panic("unreachable")
}

func (w *writer) ifStmt(stmt *syntax.IfStmt) {
	w.Sync(pkgbits.SyncIfStmt)
	w.openScope(stmt.Pos())
	w.pos(stmt)
	w.stmt(stmt.Init)
	w.expr(stmt.Cond)
	w.blockStmt(stmt.Then)
	w.stmt(stmt.Else)
	w.closeAnotherScope()
}

func (w *writer) selectStmt(stmt *syntax.SelectStmt) {
	w.Sync(pkgbits.SyncSelectStmt)

	w.pos(stmt)
	w.Len(len(stmt.Body))
	for i, clause := range stmt.Body {
		if i > 0 {
			w.closeScope(clause.Pos())
		}
		w.openScope(clause.Pos())

		w.pos(clause)
		w.stmt(clause.Comm)
		w.stmts(clause.Body)
	}
	if len(stmt.Body) > 0 {
		w.closeScope(stmt.Rbrace)
	}
}

func (w *writer) switchStmt(stmt *syntax.SwitchStmt) {
	w.Sync(pkgbits.SyncSwitchStmt)

	w.openScope(stmt.Pos())
	w.pos(stmt)
	w.stmt(stmt.Init)

	var iface, tagType types2.Type
	if guard, ok := stmt.Tag.(*syntax.TypeSwitchGuard); w.Bool(ok) {
		iface = w.p.typeOf(guard.X)

		w.pos(guard)
		if tag := guard.Lhs; w.Bool(tag != nil) {
			w.pos(tag)

			// Like w.localIdent, but we don't have a types2.Object.
			w.Sync(pkgbits.SyncLocalIdent)
			w.pkg(w.p.curpkg)
			w.String(tag.Value)
		}
		w.expr(guard.X)
	} else {
		tag := stmt.Tag

		if tag != nil {
			tagType = w.p.typeOf(tag)
		} else {
			tagType = types2.Typ[types2.Bool]
		}

		// Walk is going to emit comparisons between the tag value and
		// each case expression, and we want these comparisons to always
		// have the same type. If there are any case values that can't be
		// converted to the tag value's type, then convert everything to
		// `any` instead.
	Outer:
		for _, clause := range stmt.Body {
			for _, cas := range unpackListExpr(clause.Cases) {
				if casType := w.p.typeOf(cas); !types2.AssignableTo(casType, tagType) {
					tagType = types2.NewInterfaceType(nil, nil)
					break Outer
				}
			}
		}

		if w.Bool(tag != nil) {
			w.implicitConvExpr(tagType, tag)
		}
	}

	w.Len(len(stmt.Body))
	for i, clause := range stmt.Body {
		if i > 0 {
			w.closeScope(clause.Pos())
		}
		w.openScope(clause.Pos())

		w.pos(clause)

		cases := unpackListExpr(clause.Cases)
		if iface != nil {
			w.Len(len(cases))
			for _, cas := range cases {
				if w.Bool(isNil(w.p, cas)) {
					continue
				}
				w.exprType(iface, cas)
			}
		} else {
			// As if w.exprList(clause.Cases),
			// but with implicit conversions to tagType.

			w.Sync(pkgbits.SyncExprList)
			w.Sync(pkgbits.SyncExprs)
			w.Len(len(cases))
			for _, cas := range cases {
				w.implicitConvExpr(tagType, cas)
			}
		}

		if obj, ok := w.p.info.Implicits[clause]; ok {
			// TODO(mdempsky): These pos details are quirkish, but also
			// necessary so the variable's position is correct for DWARF
			// scope assignment later. It would probably be better for us to
			// instead just set the variable's DWARF scoping info earlier so
			// we can give it the correct position information.
			pos := clause.Pos()
			if typs := unpackListExpr(clause.Cases); len(typs) != 0 {
				pos = typeExprEndPos(typs[len(typs)-1])
			}
			w.pos(pos)

			obj := obj.(*types2.Var)
			w.typ(obj.Type())
			w.addLocal(obj)
		}

		w.stmts(clause.Body)
	}
	if len(stmt.Body) > 0 {
		w.closeScope(stmt.Rbrace)
	}

	w.closeScope(stmt.Rbrace)
}

func (w *writer) label(label *syntax.Name) {
	w.Sync(pkgbits.SyncLabel)

	// TODO(mdempsky): Replace label strings with dense indices.
	w.String(label.Value)
}

func (w *writer) optLabel(label *syntax.Name) {
	w.Sync(pkgbits.SyncOptLabel)
	if w.Bool(label != nil) {
		w.label(label)
	}
}

// @@@ Expressions

// expr writes the given expression into the function body bitstream.
func (w *writer) expr(expr syntax.Expr) {
	base.Assertf(expr != nil, "missing expression")

	expr = unparen(expr) // skip parens; unneeded after typecheck

	obj, inst := lookupObj(w.p, expr)
	targs := inst.TypeArgs

	if tv, ok := w.p.maybeTypeAndValue(expr); ok {
		if tv.IsType() {
			w.p.fatalf(expr, "unexpected type expression %v", syntax.String(expr))
		}

		if tv.Value != nil {
			w.Code(exprConst)
			w.pos(expr)
			typ := idealType(tv)
			assert(typ != nil)
			w.typ(typ)
			w.Value(tv.Value)

			// TODO(mdempsky): These details are only important for backend
			// diagnostics. Explore writing them out separately.
			w.op(constExprOp(expr))
			w.String(syntax.String(expr))
			return
		}

		if _, isNil := obj.(*types2.Nil); isNil {
			w.Code(exprNil)
			w.pos(expr)
			w.typ(tv.Type)
			return
		}

		// With shape types (and particular pointer shaping), we may have
		// an expression of type "go.shape.*uint8", but need to reshape it
		// to another shape-identical type to allow use in field
		// selection, indexing, etc.
		if typ := tv.Type; !tv.IsBuiltin() && !isTuple(typ) && !isUntyped(typ) {
			w.Code(exprReshape)
			w.typ(typ)
			// fallthrough
		}
	}

	if obj != nil {
		if targs.Len() != 0 {
			obj := obj.(*types2.Func)

			w.Code(exprFuncInst)
			w.pos(expr)
			w.funcInst(obj, targs)
			return
		}

		if isGlobal(obj) {
			w.Code(exprGlobal)
			w.obj(obj, nil)
			return
		}

		obj := obj.(*types2.Var)
		assert(!obj.IsField())

		w.Code(exprLocal)
		w.useLocal(expr.Pos(), obj)
		return
	}

	switch expr := expr.(type) {
	default:
		w.p.unexpected("expression", expr)

	case *syntax.CompositeLit:
		w.Code(exprCompLit)
		w.compLit(expr)

	case *syntax.FuncLit:
		w.Code(exprFuncLit)
		w.funcLit(expr)

	case *syntax.SelectorExpr:
		sel, ok := w.p.info.Selections[expr]
		assert(ok)

		switch sel.Kind() {
		default:
			w.p.fatalf(expr, "unexpected selection kind: %v", sel.Kind())

		case types2.FieldVal:
			w.Code(exprFieldVal)
			w.expr(expr.X)
			w.pos(expr)
			w.selector(sel.Obj())

		case types2.MethodVal:
			w.Code(exprMethodVal)
			typ := w.recvExpr(expr, sel)
			w.pos(expr)
			w.methodExpr(expr, typ, sel)

		case types2.MethodExpr:
			w.Code(exprMethodExpr)

			tv := w.p.typeAndValue(expr.X)
			assert(tv.IsType())

			index := sel.Index()
			implicits := index[:len(index)-1]

			typ := tv.Type
			w.typ(typ)

			w.Len(len(implicits))
			for _, ix := range implicits {
				w.Len(ix)
				typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
			}

			recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
			if w.Bool(isPtrTo(typ, recv)) { // need deref
				typ = recv
			} else if w.Bool(isPtrTo(recv, typ)) { // need addr
				typ = recv
			}

			w.pos(expr)
			w.methodExpr(expr, typ, sel)
		}

	case *syntax.IndexExpr:
		_ = w.p.typeOf(expr.Index) // ensure this is an index expression, not an instantiation

		xtyp := w.p.typeOf(expr.X)

		var keyType types2.Type
		if mapType, ok := types2.CoreType(xtyp).(*types2.Map); ok {
			keyType = mapType.Key()
		}

		w.Code(exprIndex)
		w.expr(expr.X)
		w.pos(expr)
		w.implicitConvExpr(keyType, expr.Index)
		if keyType != nil {
			w.rtype(xtyp)
		}

	case *syntax.SliceExpr:
		w.Code(exprSlice)
		w.expr(expr.X)
		w.pos(expr)
		for _, n := range &expr.Index {
			w.optExpr(n)
		}

	case *syntax.AssertExpr:
		iface := w.p.typeOf(expr.X)

		w.Code(exprAssert)
		w.expr(expr.X)
		w.pos(expr)
		w.exprType(iface, expr.Type)
		w.rtype(iface)

	case *syntax.Operation:
		if expr.Y == nil {
			w.Code(exprUnaryOp)
			w.op(unOps[expr.Op])
			w.pos(expr)
			w.expr(expr.X)
			break
		}

		var commonType types2.Type
		switch expr.Op {
		case syntax.Shl, syntax.Shr:
			// ok: operands are allowed to have different types
		default:
			xtyp := w.p.typeOf(expr.X)
			ytyp := w.p.typeOf(expr.Y)
			switch {
			case types2.AssignableTo(xtyp, ytyp):
				commonType = ytyp
			case types2.AssignableTo(ytyp, xtyp):
				commonType = xtyp
			default:
				w.p.fatalf(expr, "failed to find common type between %v and %v", xtyp, ytyp)
			}
		}

		w.Code(exprBinaryOp)
		w.op(binOps[expr.Op])
		w.implicitConvExpr(commonType, expr.X)
		w.pos(expr)
		w.implicitConvExpr(commonType, expr.Y)

	case *syntax.CallExpr:
		tv := w.p.typeAndValue(expr.Fun)
		if tv.IsType() {
			assert(len(expr.ArgList) == 1)
			assert(!expr.HasDots)
			w.convertExpr(tv.Type, expr.ArgList[0], false)
			break
		}

		var rtype types2.Type
		if tv.IsBuiltin() {
			switch obj, _ := lookupObj(w.p, expr.Fun); obj.Name() {
			case "make":
				assert(len(expr.ArgList) >= 1)
				assert(!expr.HasDots)

				w.Code(exprMake)
				w.pos(expr)
				w.exprType(nil, expr.ArgList[0])
				w.exprs(expr.ArgList[1:])

				typ := w.p.typeOf(expr)
				switch coreType := types2.CoreType(typ).(type) {
				default:
					w.p.fatalf(expr, "unexpected core type: %v", coreType)
				case *types2.Chan:
					w.rtype(typ)
				case *types2.Map:
					w.rtype(typ)
				case *types2.Slice:
					w.rtype(sliceElem(typ))
				}

				return

			case "new":
				assert(len(expr.ArgList) == 1)
				assert(!expr.HasDots)

				w.Code(exprNew)
				w.pos(expr)
				w.exprType(nil, expr.ArgList[0])
				return

			case "append":
				rtype = sliceElem(w.p.typeOf(expr))
			case "copy":
				typ := w.p.typeOf(expr.ArgList[0])
				if tuple, ok := typ.(*types2.Tuple); ok { // "copy(g())"
					typ = tuple.At(0).Type()
				}
				rtype = sliceElem(typ)
			case "delete":
				typ := w.p.typeOf(expr.ArgList[0])
				if tuple, ok := typ.(*types2.Tuple); ok { // "delete(g())"
					typ = tuple.At(0).Type()
				}
				rtype = typ
			case "Slice":
				rtype = sliceElem(w.p.typeOf(expr))
			}
		}

		writeFunExpr := func() {
			fun := unparen(expr.Fun)

			if selector, ok := fun.(*syntax.SelectorExpr); ok {
				if sel, ok := w.p.info.Selections[selector]; ok && sel.Kind() == types2.MethodVal {
					w.Bool(true) // method call
					typ := w.recvExpr(selector, sel)
					w.methodExpr(selector, typ, sel)
					return
				}
			}

			w.Bool(false) // not a method call (i.e., normal function call)

			if obj, inst := lookupObj(w.p, fun); w.Bool(obj != nil && inst.TypeArgs.Len() != 0) {
				obj := obj.(*types2.Func)

				w.pos(fun)
				w.funcInst(obj, inst.TypeArgs)
				return
			}

			w.expr(fun)
		}

		sigType := types2.CoreType(tv.Type).(*types2.Signature)
		paramTypes := sigType.Params()

		w.Code(exprCall)
		writeFunExpr()
		w.pos(expr)

		paramType := func(i int) types2.Type {
			if sigType.Variadic() && !expr.HasDots && i >= paramTypes.Len()-1 {
				return paramTypes.At(paramTypes.Len() - 1).Type().(*types2.Slice).Elem()
			}
			return paramTypes.At(i).Type()
		}

		w.multiExpr(expr, paramType, expr.ArgList)
		w.Bool(expr.HasDots)
		if rtype != nil {
			w.rtype(rtype)
		}
	}
}

func sliceElem(typ types2.Type) types2.Type {
	return types2.CoreType(typ).(*types2.Slice).Elem()
}

func (w *writer) optExpr(expr syntax.Expr) {
	if w.Bool(expr != nil) {
		w.expr(expr)
	}
}

// recvExpr writes out expr.X, but handles any implicit addressing,
// dereferencing, and field selections appropriate for the method
// selection.
func (w *writer) recvExpr(expr *syntax.SelectorExpr, sel *types2.Selection) types2.Type {
	index := sel.Index()
	implicits := index[:len(index)-1]

	w.Code(exprRecv)
	w.expr(expr.X)
	w.pos(expr)
	w.Len(len(implicits))

	typ := w.p.typeOf(expr.X)
	for _, ix := range implicits {
		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
		w.Len(ix)
	}

	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
	if w.Bool(isPtrTo(typ, recv)) { // needs deref
		typ = recv
	} else if w.Bool(isPtrTo(recv, typ)) { // needs addr
		typ = recv
	}

	return typ
}

// funcInst writes a reference to an instantiated function.
func (w *writer) funcInst(obj *types2.Func, targs *types2.TypeList) {
	info := w.p.objInstIdx(obj, targs, w.dict)

	// Type arguments list contains derived types; we can emit a static
	// call to the shaped function, but need to dynamically compute the
	// runtime dictionary pointer.
	if w.Bool(info.anyDerived()) {
		w.Len(w.dict.subdictIdx(info))
		return
	}

	// Type arguments list is statically known; we can emit a static
	// call with a statically reference to the respective runtime
	// dictionary.
	w.objInfo(info)
}

// methodExpr writes out a reference to the method selected by
// expr. sel should be the corresponding types2.Selection, and recv
// the type produced after any implicit addressing, dereferencing, and
// field selection. (Note: recv might differ from sel.Obj()'s receiver
// parameter in the case of interface types, and is needed for
// handling type parameter methods.)
func (w *writer) methodExpr(expr *syntax.SelectorExpr, recv types2.Type, sel *types2.Selection) {