[dev.typeparams] cmd/compile: add types2-based noder

This CL adds "irgen", a new noding implementation that utilizes types2
to guide IR construction. Notably, it completely skips dealing with
constant and type expressions (aside from using ir.TypeNode to
interoperate with the types1 typechecker), because types2 already
handled those. It also omits any syntax checking, trusting that types2
already rejected any errors.

It currently still utilizes the types1 typechecker for the desugaring
operations it handles (e.g., turning OAS2 into OAS2FUNC/etc, inserting
implicit conversions, rewriting f(g()) functions, and so on). However,
the IR is constructed in a fully incremental fashion, so it should be
easy to now piecemeal replace those dependencies as needed.

Nearly all of "go test std cmd" passes with -G=3 enabled by
default. The main remaining blocker is the number of test/run.go
failures. There also appear to be cases where types2 does not provide
us with position information. These will be iterated upon.

Portions and ideas from Dan Scales's CL 276653.

Change-Id: Ic99e8f2d0267b0312d30c10d5d043f5817a59c9d
Reviewed-on: https://go-review.googlesource.com/c/go/+/281932
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/noder/decl.go

@@ -0,0 +1,222 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+)
+
+// TODO(mdempsky): Skip blank declarations? Probably only safe
+// for declarations without pragmas.
+
+func (g *irgen) decls(decls []syntax.Decl) []ir.Node {
+	var res ir.Nodes
+	for _, decl := range decls {
+		switch decl := decl.(type) {
+		case *syntax.ConstDecl:
+			g.constDecl(&res, decl)
+		case *syntax.FuncDecl:
+			g.funcDecl(&res, decl)
+		case *syntax.TypeDecl:
+			if ir.CurFunc == nil {
+				continue // already handled in irgen.generate
+			}
+			g.typeDecl(&res, decl)
+		case *syntax.VarDecl:
+			g.varDecl(&res, decl)
+		default:
+			g.unhandled("declaration", decl)
+		}
+	}
+	return res
+}
+
+func (g *irgen) importDecl(p *noder, decl *syntax.ImportDecl) {
+	// TODO(mdempsky): Merge with gcimports so we don't have to import
+	// packages twice.
+
+	g.pragmaFlags(decl.Pragma, 0)
+
+	ipkg := importfile(decl)
+	if ipkg == ir.Pkgs.Unsafe {
+		p.importedUnsafe = true
+	}
+}
+
+func (g *irgen) constDecl(out *ir.Nodes, decl *syntax.ConstDecl) {
+	g.pragmaFlags(decl.Pragma, 0)
+
+	for _, name := range decl.NameList {
+		name, obj := g.def(name)
+		name.SetVal(obj.(*types2.Const).Val())
+		out.Append(ir.NewDecl(g.pos(decl), ir.ODCLCONST, name))
+	}
+}
+
+func (g *irgen) funcDecl(out *ir.Nodes, decl *syntax.FuncDecl) {
+	fn := ir.NewFunc(g.pos(decl))
+	fn.Nname, _ = g.def(decl.Name)
+	fn.Nname.Func = fn
+	fn.Nname.Defn = fn
+
+	fn.Pragma = g.pragmaFlags(decl.Pragma, funcPragmas)
+	if fn.Pragma&ir.Systemstack != 0 && fn.Pragma&ir.Nosplit != 0 {
+		base.ErrorfAt(fn.Pos(), "go:nosplit and go:systemstack cannot be combined")
+	}
+
+	if decl.Name.Value == "init" && decl.Recv == nil {
+		g.target.Inits = append(g.target.Inits, fn)
+	}
+
+	g.funcBody(fn, decl.Recv, decl.Type, decl.Body)
+
+	out.Append(fn)
+}
+
+func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
+	if decl.Alias {
+		if !types.AllowsGoVersion(types.LocalPkg, 1, 9) {
+			base.ErrorfAt(g.pos(decl), "type aliases only supported as of -lang=go1.9")
+		}
+
+		name, _ := g.def(decl.Name)
+		g.pragmaFlags(decl.Pragma, 0)
+
+		// TODO(mdempsky): This matches how typecheckdef marks aliases for
+		// export, but this won't generalize to exporting function-scoped
+		// type aliases. We should maybe just use n.Alias() instead.
+		if ir.CurFunc == nil {
+			name.Sym().Def = ir.TypeNode(name.Type())
+		}
+
+		out.Append(ir.NewDecl(g.pos(decl), ir.ODCLTYPE, name))
+		return
+	}
+
+	name, obj := g.def(decl.Name)
+	ntyp, otyp := name.Type(), obj.Type()
+	if ir.CurFunc != nil {
+		typecheck.TypeGen++
+		ntyp.Vargen = typecheck.TypeGen
+	}
+
+	pragmas := g.pragmaFlags(decl.Pragma, typePragmas)
+	name.SetPragma(pragmas) // TODO(mdempsky): Is this still needed?
+
+	if pragmas&ir.NotInHeap != 0 {
+		ntyp.SetNotInHeap(true)
+	}
+
+	// We need to use g.typeExpr(decl.Type) here to ensure that for
+	// chained, defined-type declarations like
+	//
+	//	type T U
+	//
+	//	//go:notinheap
+	//	type U struct { … }
+	//
+	// that we mark both T and U as NotInHeap. If we instead used just
+	// g.typ(otyp.Underlying()), then we'd instead set T's underlying
+	// type directly to the struct type (which is not marked NotInHeap)
+	// and fail to mark T as NotInHeap.
+	//
+	// Also, we rely here on Type.SetUnderlying allowing passing a
+	// defined type and handling forward references like from T to U
+	// above. Contrast with go/types's Named.SetUnderlying, which
+	// disallows this.
+	//
+	// [mdempsky: Subtleties like these are why I always vehemently
+	// object to new type pragmas.]
+	ntyp.SetUnderlying(g.typeExpr(decl.Type))
+
+	if otyp, ok := otyp.(*types2.Named); ok && otyp.NumMethods() != 0 {
+		methods := make([]*types.Field, otyp.NumMethods())
+		for i := range methods {
+			m := otyp.Method(i)
+			meth := g.obj(m)
+			methods[i] = types.NewField(meth.Pos(), g.selector(m), meth.Type())
+			methods[i].Nname = meth
+		}
+		ntyp.Methods().Set(methods)
+	}
+
+	out.Append(ir.NewDecl(g.pos(decl), ir.ODCLTYPE, name))
+}
+
+func (g *irgen) varDecl(out *ir.Nodes, decl *syntax.VarDecl) {
+	pos := g.pos(decl)
+	names := make([]*ir.Name, len(decl.NameList))
+	for i, name := range decl.NameList {
+		names[i], _ = g.def(name)
+	}
+	values := g.exprList(decl.Values)
+
+	if decl.Pragma != nil {
+		pragma := decl.Pragma.(*pragmas)
+		if err := varEmbed(g.makeXPos, names[0], decl, pragma); err != nil {
+			base.ErrorfAt(g.pos(decl), "%s", err.Error())
+		}
+		g.reportUnused(pragma)
+	}
+
+	var as2 *ir.AssignListStmt
+	if len(values) != 0 && len(names) != len(values) {
+		as2 = ir.NewAssignListStmt(pos, ir.OAS2, make([]ir.Node, len(names)), values)
+	}
+
+	for i, name := range names {
+		if ir.CurFunc != nil {
+			out.Append(ir.NewDecl(pos, ir.ODCL, name))
+		}
+		if as2 != nil {
+			as2.Lhs[i] = name
+			name.Defn = as2
+		} else {
+			as := ir.NewAssignStmt(pos, name, nil)
+			if len(values) != 0 {
+				as.Y = values[i]
+				name.Defn = as
+			} else if ir.CurFunc == nil {
+				name.Defn = as
+			}
+			out.Append(typecheck.Stmt(as))
+		}
+	}
+	if as2 != nil {
+		out.Append(typecheck.Stmt(as2))
+	}
+}
+
+// pragmaFlags returns any specified pragma flags included in allowed,
+// and reports errors about any other, unexpected pragmas.
+func (g *irgen) pragmaFlags(pragma syntax.Pragma, allowed ir.PragmaFlag) ir.PragmaFlag {
+	if pragma == nil {
+		return 0
+	}
+	p := pragma.(*pragmas)
+	present := p.Flag & allowed
+	p.Flag &^= allowed
+	g.reportUnused(p)
+	return present
+}
+
+// reportUnused reports errors about any unused pragmas.
+func (g *irgen) reportUnused(pragma *pragmas) {
+	for _, pos := range pragma.Pos {
+		if pos.Flag&pragma.Flag != 0 {
+			base.ErrorfAt(g.makeXPos(pos.Pos), "misplaced compiler directive")
+		}
+	}
+	if len(pragma.Embeds) > 0 {
+		for _, e := range pragma.Embeds {
+			base.ErrorfAt(g.makeXPos(e.Pos), "misplaced go:embed directive")
+		}
+	}
+}

src/cmd/compile/internal/noder/expr.go

@@ -0,0 +1,204 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+)
+
+func (g *irgen) expr(expr syntax.Expr) ir.Node {
+	// TODO(mdempsky): Change callers to not call on nil?
+	if expr == nil {
+		return nil
+	}
+
+	if expr == syntax.ImplicitOne {
+		base.Fatalf("expr of ImplicitOne")
+	}
+
+	if expr, ok := expr.(*syntax.Name); ok && expr.Value == "_" {
+		return ir.BlankNode
+	}
+
+	// TODO(mdempsky): Is there a better way to recognize and handle qualified identifiers?
+	if expr, ok := expr.(*syntax.SelectorExpr); ok {
+		if name, ok := expr.X.(*syntax.Name); ok {
+			if _, ok := g.info.Uses[name].(*types2.PkgName); ok {
+				return g.use(expr.Sel)
+			}
+		}
+	}
+
+	tv, ok := g.info.Types[expr]
+	if !ok {
+		base.FatalfAt(g.pos(expr), "missing type for %v (%T)", expr, expr)
+	}
+	switch {
+	case tv.IsBuiltin():
+		// TODO(mdempsky): Handle in CallExpr?
+		return g.use(expr.(*syntax.Name))
+	case tv.IsType():
+		return ir.TypeNode(g.typ(tv.Type))
+	case tv.IsValue(), tv.IsVoid():
+		// ok
+	default:
+		base.FatalfAt(g.pos(expr), "unrecognized type-checker result")
+	}
+
+	// Constant expression.
+	if tv.Value != nil {
+		return Const(g.pos(expr), g.typ(tv.Type), tv.Value)
+	}
+
+	// TODO(mdempsky): Remove dependency on typecheck.Expr.
+	n := typecheck.Expr(g.expr0(tv.Type, expr))
+	if !g.match(n.Type(), tv.Type, tv.HasOk()) {
+		base.FatalfAt(g.pos(expr), "expected %L to have type %v", n, tv.Type)
+	}
+	return n
+}
+
+func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
+	pos := g.pos(expr)
+
+	switch expr := expr.(type) {
+	case *syntax.Name:
+		if _, isNil := g.info.Uses[expr].(*types2.Nil); isNil {
+			return Nil(pos, g.typ(typ))
+		}
+		return g.use(expr)
+
+	case *syntax.CompositeLit:
+		return g.compLit(typ, expr)
+	case *syntax.FuncLit:
+		return g.funcLit(typ, expr)
+
+	case *syntax.AssertExpr:
+		return Assert(pos, g.expr(expr.X), g.typeExpr(expr.Type))
+	case *syntax.CallExpr:
+		return Call(pos, g.expr(expr.Fun), g.exprs(expr.ArgList), expr.HasDots)
+	case *syntax.IndexExpr:
+		return Index(pos, g.expr(expr.X), g.expr(expr.Index))
+	case *syntax.ParenExpr:
+		return g.expr(expr.X) // skip parens; unneeded after parse+typecheck
+	case *syntax.SelectorExpr:
+		// TODO(mdempsky/danscales): Use g.info.Selections[expr]
+		// to resolve field/method selection. See CL 280633.
+		return ir.NewSelectorExpr(pos, ir.OXDOT, g.expr(expr.X), g.name(expr.Sel))
+	case *syntax.SliceExpr:
+		return Slice(pos, g.expr(expr.X), g.expr(expr.Index[0]), g.expr(expr.Index[1]), g.expr(expr.Index[2]))
+
+	case *syntax.Operation:
+		if expr.Y == nil {
+			return Unary(pos, g.op(expr.Op, unOps[:]), g.expr(expr.X))
+		}
+		switch op := g.op(expr.Op, binOps[:]); op {
+		case ir.OEQ, ir.ONE, ir.OLT, ir.OLE, ir.OGT, ir.OGE:
+			return Compare(pos, g.typ(typ), op, g.expr(expr.X), g.expr(expr.Y))
+		default:
+			return Binary(pos, op, g.expr(expr.X), g.expr(expr.Y))
+		}
+
+	default:
+		g.unhandled("expression", expr)
+		panic("unreachable")
+	}
+}
+
+func (g *irgen) exprList(expr syntax.Expr) []ir.Node {
+	switch expr := expr.(type) {
+	case nil:
+		return nil
+	case *syntax.ListExpr:
+		return g.exprs(expr.ElemList)
+	default:
+		return []ir.Node{g.expr(expr)}
+	}
+}
+
+func (g *irgen) exprs(exprs []syntax.Expr) []ir.Node {
+	nodes := make([]ir.Node, len(exprs))
+	for i, expr := range exprs {
+		nodes[i] = g.expr(expr)
+	}
+	return nodes
+}
+
+func (g *irgen) compLit(typ types2.Type, lit *syntax.CompositeLit) ir.Node {
+	if ptr, ok := typ.Underlying().(*types2.Pointer); ok {
+		if _, isNamed := typ.(*types2.Named); isNamed {
+			// TODO(mdempsky): Questionable, but this is
+			// currently allowed by cmd/compile, go/types,
+			// and gccgo:
+			//
+			//	type T *struct{}
+			//	var _ = []T{{}}
+			base.FatalfAt(g.pos(lit), "defined-pointer composite literal")
+		}
+		return ir.NewAddrExpr(g.pos(lit), g.compLit(ptr.Elem(), lit))
+	}
+
+	_, isStruct := typ.Underlying().(*types2.Struct)
+
+	exprs := make([]ir.Node, len(lit.ElemList))
+	for i, elem := range lit.ElemList {
+		switch elem := elem.(type) {
+		case *syntax.KeyValueExpr:
+			if isStruct {
+				exprs[i] = ir.NewStructKeyExpr(g.pos(elem), g.name(elem.Key.(*syntax.Name)), g.expr(elem.Value))
+			} else {
+				exprs[i] = ir.NewKeyExpr(g.pos(elem), g.expr(elem.Key), g.expr(elem.Value))
+			}
+		default:
+			exprs[i] = g.expr(elem)
+		}
+	}
+
+	return ir.NewCompLitExpr(g.pos(lit), ir.OCOMPLIT, ir.TypeNode(g.typ(typ)), exprs)
+}
+
+func (g *irgen) funcLit(typ types2.Type, expr *syntax.FuncLit) ir.Node {
+	fn := ir.NewFunc(g.pos(expr))
+	fn.SetIsHiddenClosure(ir.CurFunc != nil)
+
+	fn.Nname = ir.NewNameAt(g.pos(expr), typecheck.ClosureName(ir.CurFunc))
+	ir.MarkFunc(fn.Nname)
+	fn.Nname.SetType(g.typ(typ))
+	fn.Nname.Func = fn
+	fn.Nname.Defn = fn
+
+	fn.OClosure = ir.NewClosureExpr(g.pos(expr), fn)
+	fn.OClosure.SetType(fn.Nname.Type())
+	fn.OClosure.SetTypecheck(1)
+
+	g.funcBody(fn, nil, expr.Type, expr.Body)
+
+	ir.FinishCaptureNames(fn.Pos(), ir.CurFunc, fn)
+
+	// TODO(mdempsky): ir.CaptureName should probably handle
+	// copying these fields from the canonical variable.
+	for _, cv := range fn.ClosureVars {
+		cv.SetType(cv.Canonical().Type())
+		cv.SetTypecheck(1)
+		cv.SetWalkdef(1)
+	}
+
+	g.target.Decls = append(g.target.Decls, fn)
+
+	return fn.OClosure
+}
+
+func (g *irgen) typeExpr(typ syntax.Expr) *types.Type {
+	n := g.expr(typ)
+	if n.Op() != ir.OTYPE {
+		base.FatalfAt(g.pos(typ), "expected type: %L", n)
+	}
+	return n.Type()
+}

src/cmd/compile/internal/noder/func.go

@@ -0,0 +1,74 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+)
+
+func (g *irgen) funcBody(fn *ir.Func, recv *syntax.Field, sig *syntax.FuncType, block *syntax.BlockStmt) {
+	typecheck.Func(fn)
+
+	// TODO(mdempsky): Remove uses of ir.CurFunc and
+	// typecheck.DeclContext after we stop relying on typecheck
+	// for desugaring.
+	outerfn, outerctxt := ir.CurFunc, typecheck.DeclContext
+	ir.CurFunc = fn
+
+	typ := fn.Type()
+	if param := typ.Recv(); param != nil {
+		g.defParam(param, recv, ir.PPARAM)
+	}
+	for i, param := range typ.Params().FieldSlice() {
+		g.defParam(param, sig.ParamList[i], ir.PPARAM)
+	}
+	for i, result := range typ.Results().FieldSlice() {
+		g.defParam(result, sig.ResultList[i], ir.PPARAMOUT)
+	}
+
+	// We may have type-checked a call to this function already and
+	// calculated its size, including parameter offsets. Now that we've
+	// created the parameter Names, force a recalculation to ensure
+	// their offsets are correct.
+	typ.Align = 0
+	types.CalcSize(typ)
+
+	if block != nil {
+		typecheck.DeclContext = ir.PAUTO
+
+		fn.Body = g.stmts(block.List)
+		if fn.Body == nil {
+			fn.Body = []ir.Node{ir.NewBlockStmt(src.NoXPos, nil)}
+		}
+		fn.Endlineno = g.makeXPos(block.Rbrace)
+
+		if base.Flag.Dwarf {
+			g.recordScopes(fn, sig)
+		}
+	}
+
+	ir.CurFunc, typecheck.DeclContext = outerfn, outerctxt
+}
+
+func (g *irgen) defParam(param *types.Field, decl *syntax.Field, class ir.Class) {
+	typecheck.DeclContext = class
+
+	var name *ir.Name
+	if decl.Name != nil {
+		name, _ = g.def(decl.Name)
+	} else if class == ir.PPARAMOUT {
+		name = g.obj(g.info.Implicits[decl])
+	}
+
+	if name != nil {
+		param.Nname = name
+		param.Sym = name.Sym() // in case it was renamed
+	}
+}

src/cmd/compile/internal/noder/helpers.go

@@ -0,0 +1,130 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+	"go/constant"
+)
+
+// Helpers for constructing typed IR nodes.
+//
+// TODO(mdempsky): Move into their own package so they can be easily
+// reused by iimport and frontend optimizations.
+//
+// TODO(mdempsky): Update to consistently return already typechecked
+// results, rather than leaving the caller responsible for using
+// typecheck.Expr or typecheck.Stmt.
+
+// Values
+
+func Const(pos src.XPos, typ *types.Type, val constant.Value) ir.Node {
+	n := ir.NewBasicLit(pos, val)
+	n.SetType(typ)
+	return n
+}
+
+func Nil(pos src.XPos, typ *types.Type) ir.Node {
+	n := ir.NewNilExpr(pos)
+	n.SetType(typ)
+	return n
+}
+
+// Expressions
+
+func Assert(pos src.XPos, x ir.Node, typ *types.Type) ir.Node {
+	return typecheck.Expr(ir.NewTypeAssertExpr(pos, x, ir.TypeNode(typ)))
+}
+
+func Binary(pos src.XPos, op ir.Op, x, y ir.Node) ir.Node {
+	switch op {
+	case ir.OANDAND, ir.OOROR:
+		return ir.NewLogicalExpr(pos, op, x, y)
+	default:
+		return ir.NewBinaryExpr(pos, op, x, y)
+	}
+}
+
+func Call(pos src.XPos, fun ir.Node, args []ir.Node, dots bool) ir.Node {
+	// TODO(mdempsky): This should not be so difficult.
+
+	n := ir.NewCallExpr(pos, ir.OCALL, fun, args)
+	n.IsDDD = dots
+
+	// Actually a type conversion.
+	if fun.Op() == ir.OTYPE {
+		return typecheck.Expr(n)
+	}
+
+	if fun, ok := fun.(*ir.Name); ok && fun.BuiltinOp != 0 {
+		switch fun.BuiltinOp {
+		case ir.OCLOSE, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN:
+			return typecheck.Stmt(n)
+		default:
+			return typecheck.Expr(n)
+		}
+	}
+
+	// We probably already typechecked fun, and typecheck probably
+	// got it wrong because it didn't know the expression was
+	// going to be called immediately. Correct its mistakes.
+	switch fun := fun.(type) {
+	case *ir.ClosureExpr:
+		fun.Func.SetClosureCalled(true)
+	case *ir.SelectorExpr:
+		if fun.Op() == ir.OCALLPART {
+			op := ir.ODOTMETH
+			if fun.X.Type().IsInterface() {
+				op = ir.ODOTINTER
+			}
+			fun.SetOp(op)
+			fun.SetType(fun.Selection.Type)
+		}
+	}
+
+	typecheck.Call(n)
+	return n
+}
+
+func Compare(pos src.XPos, typ *types.Type, op ir.Op, x, y ir.Node) ir.Node {
+	n := typecheck.Expr(ir.NewBinaryExpr(pos, op, x, y))
+	n.SetType(typ)
+	return n
+}
+
+func Index(pos src.XPos, x, index ir.Node) ir.Node {
+	return ir.NewIndexExpr(pos, x, index)
+}
+
+func Slice(pos src.XPos, x, low, high, max ir.Node) ir.Node {
+	op := ir.OSLICE
+	if max != nil {
+		op = ir.OSLICE3
+	}
+	return ir.NewSliceExpr(pos, op, x, low, high, max)
+}
+
+func Unary(pos src.XPos, op ir.Op, x ir.Node) ir.Node {
+	switch op {
+	case ir.OADDR:
+		return typecheck.NodAddrAt(pos, x)
+	case ir.ODEREF:
+		return ir.NewStarExpr(pos, x)
+	default:
+		return ir.NewUnaryExpr(pos, op, x)
+	}
+}
+
+// Statements
+
+var one = constant.MakeInt64(1)
+
+func IncDec(pos src.XPos, op ir.Op, x ir.Node) ir.Node {
+	x = typecheck.AssignExpr(x)
+	return ir.NewAssignOpStmt(pos, op, x, typecheck.DefaultLit(ir.NewBasicLit(pos, one), x.Type()))
+}

src/cmd/compile/internal/noder/irgen.go

@@ -0,0 +1,176 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"os"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/dwarfgen"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+)
+
+// check2 type checks a Go package using types2, and then generates IR
+// using the results.
+func check2(noders []*noder) {
+	if base.SyntaxErrors() != 0 {
+		base.ErrorExit()
+	}
+
+	// setup and syntax error reporting
+	var m posMap
+	files := make([]*syntax.File, len(noders))
+	for i, p := range noders {
+		m.join(&p.posMap)
+		files[i] = p.file
+	}
+
+	// typechecking
+	conf := types2.Config{
+		InferFromConstraints:  true,
+		IgnoreBranches:        true, // parser already checked via syntax.CheckBranches mode
+		CompilerErrorMessages: true, // use error strings matching existing compiler errors
+		Error: func(err error) {
+			terr := err.(types2.Error)
+			if len(terr.Msg) > 0 && terr.Msg[0] == '\t' {
+				// types2 reports error clarifications via separate
+				// error messages which are indented with a tab.
+				// Ignore them to satisfy tools and tests that expect
+				// only one error in such cases.
+				// TODO(gri) Need to adjust error reporting in types2.
+				return
+			}
+			base.ErrorfAt(m.makeXPos(terr.Pos), "%s", terr.Msg)
+		},
+		Importer: &gcimports{
+			packages: make(map[string]*types2.Package),
+		},
+		Sizes: &gcSizes{},
+	}
+	info := types2.Info{
+		Types:      make(map[syntax.Expr]types2.TypeAndValue),
+		Defs:       make(map[*syntax.Name]types2.Object),
+		Uses:       make(map[*syntax.Name]types2.Object),
+		Selections: make(map[*syntax.SelectorExpr]*types2.Selection),
+		Implicits:  make(map[syntax.Node]types2.Object),
+		Scopes:     make(map[syntax.Node]*types2.Scope),
+		// expand as needed
+	}
+	pkg, err := conf.Check(base.Ctxt.Pkgpath, files, &info)
+	files = nil
+	if err != nil {
+		base.FatalfAt(src.NoXPos, "conf.Check error: %v", err)
+	}
+	base.ExitIfErrors()
+	if base.Flag.G < 2 {
+		os.Exit(0)
+	}
+
+	g := irgen{
+		target: typecheck.Target,
+		self:   pkg,
+		info:   &info,
+		posMap: m,
+		objs:   make(map[types2.Object]*ir.Name),
+	}
+	g.generate(noders)
+
+	if base.Flag.G < 3 {
+		os.Exit(0)
+	}
+}
+
+type irgen struct {
+	target *ir.Package
+	self   *types2.Package
+	info   *types2.Info
+
+	posMap
+	objs   map[types2.Object]*ir.Name
+	marker dwarfgen.ScopeMarker
+}
+
+func (g *irgen) generate(noders []*noder) {
+	types.LocalPkg.Name = g.self.Name()
+	typecheck.TypecheckAllowed = true
+
+	// At this point, types2 has already handled name resolution and
+	// type checking. We just need to map from its object and type
+	// representations to those currently used by the rest of the
+	// compiler. This happens mostly in 3 passes.
+
+	// 1. Process all import declarations. We use the compiler's own
+	// importer for this, rather than types2's gcimporter-derived one,
+	// to handle extensions and inline function bodies correctly.
+	//
+	// Also, we need to do this in a separate pass, because mappings are
+	// instantiated on demand. If we interleaved processing import
+	// declarations with other declarations, it's likely we'd end up
+	// wanting to map an object/type from another source file, but not
+	// yet have the import data it relies on.
+	declLists := make([][]syntax.Decl, len(noders))
+Outer:
+	for i, p := range noders {
+		g.pragmaFlags(p.file.Pragma, ir.GoBuildPragma)
+		for j, decl := range p.file.DeclList {
+			switch decl := decl.(type) {
+			case *syntax.ImportDecl:
+				g.importDecl(p, decl)
+			default:
+				declLists[i] = p.file.DeclList[j:]
+				continue Outer // no more ImportDecls
+			}
+		}
+	}
+	types.LocalPkg.Height = myheight
+
+	// 2. Process all package-block type declarations. As with imports,
+	// we need to make sure all types are properly instantiated before
+	// trying to map any expressions that utilize them. In particular,
+	// we need to make sure type pragmas are already known (see comment
+	// in irgen.typeDecl).
+	//
+	// We could perhaps instead defer processing of package-block
+	// variable initializers and function bodies, like noder does, but
+	// special-casing just package-block type declarations minimizes the
+	// differences between processing package-block and function-scoped
+	// declarations.
+	for _, declList := range declLists {
+		for _, decl := range declList {
+			switch decl := decl.(type) {
+			case *syntax.TypeDecl:
+				g.typeDecl((*ir.Nodes)(&g.target.Decls), decl)
+			}
+		}
+	}
+
+	// 3. Process all remaining declarations.
+	for _, declList := range declLists {
+		g.target.Decls = append(g.target.Decls, g.decls(declList)...)
+	}
+	typecheck.DeclareUniverse()
+
+	for _, p := range noders {
+		// Process linkname and cgo pragmas.
+		p.processPragmas()
+
+		// Double check for any type-checking inconsistencies. This can be
+		// removed once we're confident in IR generation results.
+		syntax.Walk(p.file, func(n syntax.Node) bool {
+			g.validate(n)
+			return false
+		})
+	}
+}
+
+func (g *irgen) unhandled(what string, p poser) {
+	base.FatalfAt(g.pos(p), "unhandled %s: %T", what, p)
+	panic("unreachable")
+}

src/cmd/compile/internal/noder/noder.go

@@ -23,48 +23,31 @@ import (
 	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
-	"cmd/compile/internal/types2"
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 )
 
 func LoadPackage(filenames []string) {
 	base.Timer.Start("fe", "parse")
-	lines := ParseFiles(filenames)
-	base.Timer.Stop()
-	base.Timer.AddEvent(int64(lines), "lines")
 
-	if base.Flag.G != 0 && base.Flag.G < 3 {
+	mode := syntax.CheckBranches
-		// can only parse generic code for now
+	if base.Flag.G != 0 {
-		base.ExitIfErrors()
+		mode |= syntax.AllowGenerics
-		return
 	}
 
-	// Typecheck.
-	Package()
-
-	// With all user code typechecked, it's now safe to verify unused dot imports.
-	CheckDotImports()
-	base.ExitIfErrors()
-}
-
-// ParseFiles concurrently parses files into *syntax.File structures.
-// Each declaration in every *syntax.File is converted to a syntax tree
-// and its root represented by *Node is appended to Target.Decls.
-// Returns the total count of parsed lines.
-func ParseFiles(filenames []string) (lines uint) {
-	noders := make([]*noder, 0, len(filenames))
 	// Limit the number of simultaneously open files.
 	sem := make(chan struct{}, runtime.GOMAXPROCS(0)+10)
 
-	for _, filename := range filenames {
+	noders := make([]*noder, len(filenames))
-		p := &noder{
+	for i, filename := range filenames {
+		p := noder{
 			err:         make(chan syntax.Error),
 			trackScopes: base.Flag.Dwarf,
 		}
-		noders = append(noders, p)
+		noders[i] = &p
 
-		go func(filename string) {
+		filename := filename
+		go func() {
 			sem <- struct{}{}
 			defer func() { <-sem }()
 			defer close(p.err)
@@ -77,115 +60,42 @@ func ParseFiles(filenames []string) (lines uint) {
 			}
 			defer f.Close()
 
-			mode := syntax.CheckBranches
-			if base.Flag.G != 0 {
-				mode |= syntax.AllowGenerics
-			}
 			p.file, _ = syntax.Parse(fbase, f, p.error, p.pragma, mode) // errors are tracked via p.error
-		}(filename)
+		}()
 	}
 
-	// generic noding phase (using new typechecker)
+	var lines uint
-	if base.Flag.G != 0 {
-		// setup and syntax error reporting
-		nodersmap := make(map[string]*noder)
-		var files []*syntax.File
-		for _, p := range noders {
-			for e := range p.err {
-				p.errorAt(e.Pos, "%s", e.Msg)
-			}
-
-			nodersmap[p.file.Pos().RelFilename()] = p
-			files = append(files, p.file)
-			lines += p.file.EOF.Line()
-
-		}
-		if base.SyntaxErrors() != 0 {
-			base.ErrorExit()
-		}
-
-		// typechecking
-		conf := types2.Config{
-			InferFromConstraints:  true,
-			IgnoreBranches:        true, // parser already checked via syntax.CheckBranches mode
-			CompilerErrorMessages: true, // use error strings matching existing compiler errors
-			Error: func(err error) {
-				terr := err.(types2.Error)
-				if len(terr.Msg) > 0 && terr.Msg[0] == '\t' {
-					// types2 reports error clarifications via separate
-					// error messages which are indented with a tab.
-					// Ignore them to satisfy tools and tests that expect
-					// only one error in such cases.
-					// TODO(gri) Need to adjust error reporting in types2.
-					return
-				}
-				p := nodersmap[terr.Pos.RelFilename()]
-				base.ErrorfAt(p.makeXPos(terr.Pos), "%s", terr.Msg)
-			},
-			Importer: &gcimports{
-				packages: make(map[string]*types2.Package),
-			},
-			Sizes: &gcSizes{},
-		}
-		info := types2.Info{
-			Types:      make(map[syntax.Expr]types2.TypeAndValue),
-			Defs:       make(map[*syntax.Name]types2.Object),
-			Uses:       make(map[*syntax.Name]types2.Object),
-			Selections: make(map[*syntax.SelectorExpr]*types2.Selection),
-			// expand as needed
-		}
-		conf.Check(base.Ctxt.Pkgpath, files, &info)
-		base.ExitIfErrors()
-		if base.Flag.G < 2 {
-			return
-		}
-
-		// noding
-		for _, p := range noders {
-			// errors have already been reported
-
-			p.typeInfo = &info
-			p.node()
-			lines += p.file.EOF.Line()
-			p.file = nil // release memory
-			base.ExitIfErrors()
-
-			// Always run testdclstack here, even when debug_dclstack is not set, as a sanity measure.
-			types.CheckDclstack()
-		}
-
-		types.LocalPkg.Height = myheight
-		return
-	}
-
-	// traditional (non-generic) noding phase
 	for _, p := range noders {
 		for e := range p.err {
 			p.errorAt(e.Pos, "%s", e.Msg)
 		}
-
-		p.node()
 		lines += p.file.EOF.Line()
-		p.file = nil // release memory
-		if base.SyntaxErrors() != 0 {
-			base.ErrorExit()
-		}
-
-		// Always run testdclstack here, even when debug_dclstack is not set, as a sanity measure.
-		types.CheckDclstack()
 	}
+	base.Timer.AddEvent(int64(lines), "lines")
+
+	if base.Flag.G != 0 {
+		// Use types2 to type-check and possibly generate IR.
+		check2(noders)
+		return
+	}
+
+	for _, p := range noders {
+		p.node()
+		p.file = nil // release memory
+	}
+
+	if base.SyntaxErrors() != 0 {
+		base.ErrorExit()
+	}
+	types.CheckDclstack()
 
 	for _, p := range noders {
 		p.processPragmas()
 	}
 
+	// Typecheck.
 	types.LocalPkg.Height = myheight
-	return
-}
-
-func Package() {
 	typecheck.DeclareUniverse()
-
 	typecheck.TypecheckAllowed = true
 
 	// Process top-level declarations in phases.
@@ -242,8 +152,10 @@ func Package() {
 	}
 
 	// Phase 5: With all user code type-checked, it's now safe to verify map keys.
+	// With all user code typechecked, it's now safe to verify unused dot imports.
 	typecheck.CheckMapKeys()
-
+	CheckDotImports()
+	base.ExitIfErrors()
 }
 
 func (p *noder) errorAt(pos syntax.Pos, format string, args ...interface{}) {
@@ -272,37 +184,6 @@ type noder struct {
 	trackScopes    bool
 
 	funcState *funcState
-
-	// typeInfo provides access to the type information computed by the new
-	// typechecker. It is only present if -G is set, and all noders point to
-	// the same types.Info. For now this is a local field, if need be we can
-	// make it global.
-	typeInfo *types2.Info
-}
-
-// For now we provide these basic accessors to get to type and object
-// information of expression nodes during noding. Eventually we will
-// attach this information directly to the syntax tree which should
-// simplify access and make it more efficient as well.
-
-// typ returns the type and value information for the given expression.
-func (p *noder) typ(x syntax.Expr) types2.TypeAndValue {
-	return p.typeInfo.Types[x]
-}
-
-// def returns the object for the given name in its declaration.
-func (p *noder) def(x *syntax.Name) types2.Object {
-	return p.typeInfo.Defs[x]
-}
-
-// use returns the object for the given name outside its declaration.
-func (p *noder) use(x *syntax.Name) types2.Object {
-	return p.typeInfo.Uses[x]
-}
-
-// sel returns the selection information for the given selector expression.
-func (p *noder) sel(x *syntax.SelectorExpr) *types2.Selection {
-	return p.typeInfo.Selections[x]
 }
 
 // funcState tracks all per-function state to make handling nested
@@ -380,7 +261,6 @@ type linkname struct {
 }
 
 func (p *noder) node() {
-	types.Block = 1
 	p.importedUnsafe = false
 	p.importedEmbed = false
 

src/cmd/compile/internal/noder/object.go

@@ -0,0 +1,169 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+)
+
+func (g *irgen) def(name *syntax.Name) (*ir.Name, types2.Object) {
+	obj, ok := g.info.Defs[name]
+	if !ok {
+		base.FatalfAt(g.pos(name), "unknown name %v", name)
+	}
+	return g.obj(obj), obj
+}
+
+func (g *irgen) use(name *syntax.Name) *ir.Name {
+	obj, ok := g.info.Uses[name]
+	if !ok {
+		base.FatalfAt(g.pos(name), "unknown name %v", name)
+	}
+	return ir.CaptureName(g.pos(obj), ir.CurFunc, g.obj(obj))
+}
+
+// obj returns the Name that represents the given object. If no such
+// Name exists yet, it will be implicitly created.
+//
+// For objects declared at function scope, ir.CurFunc must already be
+// set to the respective function when the Name is created.
+func (g *irgen) obj(obj types2.Object) *ir.Name {
+	// For imported objects, we use iimport directly instead of mapping
+	// the types2 representation.
+	if obj.Pkg() != g.self {
+		sym := g.sym(obj)
+		if sym.Def != nil {
+			return sym.Def.(*ir.Name)
+		}
+		n := typecheck.Resolve(ir.NewIdent(src.NoXPos, sym))
+		if n, ok := n.(*ir.Name); ok {
+			return n
+		}
+		base.FatalfAt(g.pos(obj), "failed to resolve %v", obj)
+	}
+
+	if name, ok := g.objs[obj]; ok {
+		return name // previously mapped
+	}
+
+	var name *ir.Name
+	pos := g.pos(obj)
+
+	class := typecheck.DeclContext
+	if obj.Parent() == g.self.Scope() {
+		class = ir.PEXTERN // forward reference to package-block declaration
+	}
+
+	// "You are in a maze of twisting little passages, all different."
+	switch obj := obj.(type) {
+	case *types2.Const:
+		name = g.objCommon(pos, ir.OLITERAL, g.sym(obj), class, g.typ(obj.Type()))
+
+	case *types2.Func:
+		sig := obj.Type().(*types2.Signature)
+		var sym *types.Sym
+		var typ *types.Type
+		if recv := sig.Recv(); recv == nil {
+			if obj.Name() == "init" {
+				sym = renameinit()
+			} else {
+				sym = g.sym(obj)
+			}
+			typ = g.typ(sig)
+		} else {
+			sym = ir.MethodSym(g.typ(recv.Type()), g.selector(obj))
+			typ = g.signature(g.param(recv), sig)
+		}
+		name = g.objCommon(pos, ir.ONAME, sym, ir.PFUNC, typ)
+
+	case *types2.TypeName:
+		if obj.IsAlias() {
+			name = g.objCommon(pos, ir.OTYPE, g.sym(obj), class, g.typ(obj.Type()))
+		} else {
+			name = ir.NewDeclNameAt(pos, ir.OTYPE, g.sym(obj))
+			g.objFinish(name, class, types.NewNamed(name))
+		}
+
+	case *types2.Var:
+		var sym *types.Sym
+		if class == ir.PPARAMOUT {
+			// Backend needs names for result parameters,
+			// even if they're anonymous or blank.
+			switch obj.Name() {
+			case "":
+				sym = typecheck.LookupNum("~r", len(ir.CurFunc.Dcl)) // 'r' for "result"
+			case "_":
+				sym = typecheck.LookupNum("~b", len(ir.CurFunc.Dcl)) // 'b' for "blank"
+			}
+		}
+		if sym == nil {
+			sym = g.sym(obj)
+		}
+		name = g.objCommon(pos, ir.ONAME, sym, class, g.typ(obj.Type()))
+
+	default:
+		g.unhandled("object", obj)
+	}
+
+	g.objs[obj] = name
+	return name
+}
+
+func (g *irgen) objCommon(pos src.XPos, op ir.Op, sym *types.Sym, class ir.Class, typ *types.Type) *ir.Name {
+	name := ir.NewDeclNameAt(pos, op, sym)
+	g.objFinish(name, class, typ)
+	return name
+}
+
+func (g *irgen) objFinish(name *ir.Name, class ir.Class, typ *types.Type) {
+	sym := name.Sym()
+
+	name.SetType(typ)
+	name.Class = class
+	if name.Class == ir.PFUNC {
+		sym.SetFunc(true)
+	}
+
+	// We already know name's type, but typecheck is really eager to try
+	// recomputing it later. This appears to prevent that at least.
+	name.Ntype = ir.TypeNode(typ)
+	name.SetTypecheck(1)
+	name.SetWalkdef(1)
+
+	if ir.IsBlank(name) {
+		return
+	}
+
+	switch class {
+	case ir.PEXTERN:
+		g.target.Externs = append(g.target.Externs, name)
+		fallthrough
+	case ir.PFUNC:
+		sym.Def = name
+		if name.Class == ir.PFUNC && name.Type().Recv() != nil {
+			break // methods are exported with their receiver type
+		}
+		if types.IsExported(sym.Name) {
+			typecheck.Export(name)
+		}
+		if base.Flag.AsmHdr != "" && !name.Sym().Asm() {
+			name.Sym().SetAsm(true)
+			g.target.Asms = append(g.target.Asms, name)
+		}
+
+	default:
+		// Function-scoped declaration.
+		name.Curfn = ir.CurFunc
+		if name.Op() == ir.ONAME {
+			ir.CurFunc.Dcl = append(ir.CurFunc.Dcl, name)
+		}
+	}
+}

src/cmd/compile/internal/noder/posmap.go

@@ -27,7 +27,8 @@ func (m *posMap) end(p ender) src.XPos { return m.makeXPos(p.End()) }
 
 func (m *posMap) makeXPos(pos syntax.Pos) src.XPos {
 	if !pos.IsKnown() {
-		base.Fatalf("unknown position")
+		// TODO(mdempsky): Investigate restoring base.Fatalf.
+		return src.NoXPos
 	}
 
 	posBase := m.makeSrcPosBase(pos.Base())
@@ -70,6 +71,9 @@ func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
 }
 
 func (m *posMap) join(other *posMap) {
+	if m.bases == nil {
+		m.bases = make(map[*syntax.PosBase]*src.PosBase)
+	}
 	for k, v := range other.bases {
 		if m.bases[k] != nil {
 			base.Fatalf("duplicate posmap bases")

src/cmd/compile/internal/noder/scopes.go

@@ -0,0 +1,64 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"strings"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/types2"
+)
+
+// recordScopes populates fn.Parents and fn.Marks based on the scoping
+// information provided by types2.
+func (g *irgen) recordScopes(fn *ir.Func, sig *syntax.FuncType) {
+	scope, ok := g.info.Scopes[sig]
+	if !ok {
+		base.FatalfAt(fn.Pos(), "missing scope for %v", fn)
+	}
+
+	for i, n := 0, scope.NumChildren(); i < n; i++ {
+		g.walkScope(scope.Child(i))
+	}
+
+	g.marker.WriteTo(fn)
+}
+
+func (g *irgen) walkScope(scope *types2.Scope) bool {
+	// types2 doesn't provide a proper API for determining the
+	// lexical element a scope represents, so we have to resort to
+	// string matching. Conveniently though, this allows us to
+	// skip both function types and function literals, neither of
+	// which are interesting to us here.
+	if strings.HasPrefix(scope.String(), "function scope ") {
+		return false
+	}
+
+	g.marker.Push(g.pos(scope))
+
+	haveVars := false
+	for _, name := range scope.Names() {
+		if obj, ok := scope.Lookup(name).(*types2.Var); ok && obj.Name() != "_" {
+			haveVars = true
+			break
+		}
+	}
+
+	for i, n := 0, scope.NumChildren(); i < n; i++ {
+		if g.walkScope(scope.Child(i)) {
+			haveVars = true
+		}
+	}
+
+	if haveVars {
+		g.marker.Pop(g.end(scope))
+	} else {
+		g.marker.Unpush()
+	}
+
+	return haveVars
+}

src/cmd/compile/internal/noder/stmt.go

@@ -0,0 +1,280 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+)
+
+func (g *irgen) stmts(stmts []syntax.Stmt) []ir.Node {
+	var nodes []ir.Node
+	for _, stmt := range stmts {
+		switch s := g.stmt(stmt).(type) {
+		case nil: // EmptyStmt
+		case *ir.BlockStmt:
+			nodes = append(nodes, s.List...)
+		default:
+			nodes = append(nodes, s)
+		}
+	}
+	return nodes
+}
+
+func (g *irgen) stmt(stmt syntax.Stmt) ir.Node {
+	// TODO(mdempsky): Remove dependency on typecheck.
+	return typecheck.Stmt(g.stmt0(stmt))
+}
+
+func (g *irgen) stmt0(stmt syntax.Stmt) ir.Node {
+	switch stmt := stmt.(type) {
+	case nil, *syntax.EmptyStmt:
+		return nil
+	case *syntax.LabeledStmt:
+		return g.labeledStmt(stmt)
+	case *syntax.BlockStmt:
+		return ir.NewBlockStmt(g.pos(stmt), g.blockStmt(stmt))
+	case *syntax.ExprStmt:
+		x := g.expr(stmt.X)
+		if call, ok := x.(*ir.CallExpr); ok {
+			call.Use = ir.CallUseStmt
+		}
+		return x
+	case *syntax.SendStmt:
+		return ir.NewSendStmt(g.pos(stmt), g.expr(stmt.Chan), g.expr(stmt.Value))
+	case *syntax.DeclStmt:
+		return ir.NewBlockStmt(g.pos(stmt), g.decls(stmt.DeclList))
+
+	case *syntax.AssignStmt:
+		if stmt.Op != 0 && stmt.Op != syntax.Def {
+			op := g.op(stmt.Op, binOps[:])
+			if stmt.Rhs == syntax.ImplicitOne {
+				return IncDec(g.pos(stmt), op, g.expr(stmt.Lhs))
+			}
+			return ir.NewAssignOpStmt(g.pos(stmt), op, g.expr(stmt.Lhs), g.expr(stmt.Rhs))
+		}
+
+		rhs := g.exprList(stmt.Rhs)
+		if list, ok := stmt.Lhs.(*syntax.ListExpr); ok && len(list.ElemList) != 1 || len(rhs) != 1 {
+			n := ir.NewAssignListStmt(g.pos(stmt), ir.OAS2, nil, nil)
+			n.Def = stmt.Op == syntax.Def
+			n.Lhs = g.assignList(stmt.Lhs, n, n.Def)
+			n.Rhs = rhs
+			return n
+		}
+
+		n := ir.NewAssignStmt(g.pos(stmt), nil, nil)
+		n.Def = stmt.Op == syntax.Def
+		n.X = g.assignList(stmt.Lhs, n, n.Def)[0]
+		n.Y = rhs[0]
+		return n
+
+	case *syntax.BranchStmt:
+		return ir.NewBranchStmt(g.pos(stmt), g.tokOp(int(stmt.Tok), branchOps[:]), g.name(stmt.Label))
+	case *syntax.CallStmt:
+		return ir.NewGoDeferStmt(g.pos(stmt), g.tokOp(int(stmt.Tok), callOps[:]), g.expr(stmt.Call))
+	case *syntax.ReturnStmt:
+		return ir.NewReturnStmt(g.pos(stmt), g.exprList(stmt.Results))
+	case *syntax.IfStmt:
+		return g.ifStmt(stmt)
+	case *syntax.ForStmt:
+		return g.forStmt(stmt)
+	case *syntax.SelectStmt:
+		return g.selectStmt(stmt)
+	case *syntax.SwitchStmt:
+		return g.switchStmt(stmt)
+
+	default:
+		g.unhandled("statement", stmt)
+		panic("unreachable")
+	}
+}
+
+// TODO(mdempsky): Investigate replacing with switch statements or dense arrays.
+
+var branchOps = [...]ir.Op{
+	syntax.Break:       ir.OBREAK,
+	syntax.Continue:    ir.OCONTINUE,
+	syntax.Fallthrough: ir.OFALL,
+	syntax.Goto:        ir.OGOTO,
+}
+
+var callOps = [...]ir.Op{
+	syntax.Defer: ir.ODEFER,
+	syntax.Go:    ir.OGO,
+}
+
+func (g *irgen) tokOp(tok int, ops []ir.Op) ir.Op {
+	// TODO(mdempsky): Validate.
+	return ops[tok]
+}
+
+func (g *irgen) op(op syntax.Operator, ops []ir.Op) ir.Op {
+	// TODO(mdempsky): Validate.
+	return ops[op]
+}
+
+func (g *irgen) assignList(expr syntax.Expr, defn ir.InitNode, colas bool) []ir.Node {
+	if !colas {
+		return g.exprList(expr)
+	}
+
+	var exprs []syntax.Expr
+	if list, ok := expr.(*syntax.ListExpr); ok {
+		exprs = list.ElemList
+	} else {
+		exprs = []syntax.Expr{expr}
+	}
+
+	res := make([]ir.Node, len(exprs))
+	for i, expr := range exprs {
+		expr := expr.(*syntax.Name)
+		if expr.Value == "_" {
+			res[i] = ir.BlankNode
+			continue
+		}
+
+		if obj, ok := g.info.Uses[expr]; ok {
+			res[i] = g.obj(obj)
+			continue
+		}
+
+		name, _ := g.def(expr)
+		name.Defn = defn
+		defn.PtrInit().Append(ir.NewDecl(name.Pos(), ir.ODCL, name))
+		res[i] = name
+	}
+	return res
+}
+
+func (g *irgen) blockStmt(stmt *syntax.BlockStmt) []ir.Node {
+	return g.stmts(stmt.List)
+}
+
+func (g *irgen) ifStmt(stmt *syntax.IfStmt) ir.Node {
+	init := g.stmt(stmt.Init)
+	n := ir.NewIfStmt(g.pos(stmt), g.expr(stmt.Cond), g.blockStmt(stmt.Then), nil)
+	if stmt.Else != nil {
+		e := g.stmt(stmt.Else)
+		if e.Op() == ir.OBLOCK {
+			e := e.(*ir.BlockStmt)
+			n.Else = e.List
+		} else {
+			n.Else = []ir.Node{e}
+		}
+	}
+	return g.init(init, n)
+}
+
+func (g *irgen) forStmt(stmt *syntax.ForStmt) ir.Node {
+	if r, ok := stmt.Init.(*syntax.RangeClause); ok {
+		n := ir.NewRangeStmt(g.pos(r), nil, nil, g.expr(r.X), nil)
+		if r.Lhs != nil {
+			n.Def = r.Def
+			lhs := g.assignList(r.Lhs, n, n.Def)
+			n.Key = lhs[0]
+			if len(lhs) > 1 {
+				n.Value = lhs[1]
+			}
+		}
+		n.Body = g.blockStmt(stmt.Body)
+		return n
+	}
+
+	return ir.NewForStmt(g.pos(stmt), g.stmt(stmt.Init), g.expr(stmt.Cond), g.stmt(stmt.Post), g.blockStmt(stmt.Body))
+}
+
+func (g *irgen) selectStmt(stmt *syntax.SelectStmt) ir.Node {
+	body := make([]*ir.CommClause, len(stmt.Body))
+	for i, clause := range stmt.Body {
+		body[i] = ir.NewCommStmt(g.pos(clause), g.stmt(clause.Comm), g.stmts(clause.Body))
+	}
+	return ir.NewSelectStmt(g.pos(stmt), body)
+}
+
+func (g *irgen) switchStmt(stmt *syntax.SwitchStmt) ir.Node {
+	pos := g.pos(stmt)
+	init := g.stmt(stmt.Init)
+
+	var expr ir.Node
+	switch tag := stmt.Tag.(type) {
+	case *syntax.TypeSwitchGuard:
+		var ident *ir.Ident
+		if tag.Lhs != nil {
+			ident = ir.NewIdent(g.pos(tag.Lhs), g.name(tag.Lhs))
+		}
+		expr = ir.NewTypeSwitchGuard(pos, ident, g.expr(tag.X))
+	default:
+		expr = g.expr(tag)
+	}
+
+	body := make([]*ir.CaseClause, len(stmt.Body))
+	for i, clause := range stmt.Body {
+		// Check for an implicit clause variable before
+		// visiting body, because it may contain function
+		// literals that reference it, and then it'll be
+		// associated to the wrong function.
+		//
+		// Also, override its position to the clause's colon, so that
+		// dwarfgen can find the right scope for it later.
+		// TODO(mdempsky): We should probably just store the scope
+		// directly in the ir.Name.
+		var cv *ir.Name
+		if obj, ok := g.info.Implicits[clause]; ok {
+			cv = g.obj(obj)
+			cv.SetPos(g.makeXPos(clause.Colon))
+		}
+		body[i] = ir.NewCaseStmt(g.pos(clause), g.exprList(clause.Cases), g.stmts(clause.Body))
+		body[i].Var = cv
+	}
+
+	return g.init(init, ir.NewSwitchStmt(pos, expr, body))
+}
+
+func (g *irgen) labeledStmt(label *syntax.LabeledStmt) ir.Node {
+	sym := g.name(label.Label)
+	lhs := ir.NewLabelStmt(g.pos(label), sym)
+	ls := g.stmt(label.Stmt)
+
+	// Attach label directly to control statement too.
+	switch ls := ls.(type) {
+	case *ir.ForStmt:
+		ls.Label = sym
+	case *ir.RangeStmt:
+		ls.Label = sym
+	case *ir.SelectStmt:
+		ls.Label = sym
+	case *ir.SwitchStmt:
+		ls.Label = sym
+	}
+
+	l := []ir.Node{lhs}
+	if ls != nil {
+		if ls.Op() == ir.OBLOCK {
+			ls := ls.(*ir.BlockStmt)
+			l = append(l, ls.List...)
+		} else {
+			l = append(l, ls)
+		}
+	}
+	return ir.NewBlockStmt(src.NoXPos, l)
+}
+
+func (g *irgen) init(init ir.Node, stmt ir.InitNode) ir.InitNode {
+	if init != nil {
+		stmt.SetInit([]ir.Node{init})
+	}
+	return stmt
+}
+
+func (g *irgen) name(name *syntax.Name) *types.Sym {
+	if name == nil {
+		return nil
+	}
+	return typecheck.Lookup(name.Value)
+}

src/cmd/compile/internal/noder/types.go

@@ -0,0 +1,208 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+)
+
+func (g *irgen) pkg(pkg *types2.Package) *types.Pkg {
+	switch pkg {
+	case nil:
+		return types.BuiltinPkg
+	case g.self:
+		return types.LocalPkg
+	case types2.Unsafe:
+		return ir.Pkgs.Unsafe
+	}
+	return types.NewPkg(pkg.Path(), pkg.Name())
+}
+
+func (g *irgen) typ(typ types2.Type) *types.Type {
+	switch typ := typ.(type) {
+	case *types2.Basic:
+		return g.basic(typ)
+	case *types2.Named:
+		obj := g.obj(typ.Obj())
+		if obj.Op() != ir.OTYPE {
+			base.FatalfAt(obj.Pos(), "expected type: %L", obj)
+		}
+		return obj.Type()
+
+	case *types2.Array:
+		return types.NewArray(g.typ(typ.Elem()), typ.Len())
+	case *types2.Chan:
+		return types.NewChan(g.typ(typ.Elem()), dirs[typ.Dir()])
+	case *types2.Map:
+		return types.NewMap(g.typ(typ.Key()), g.typ(typ.Elem()))
+	case *types2.Pointer:
+		return types.NewPtr(g.typ(typ.Elem()))
+	case *types2.Signature:
+		return g.signature(nil, typ)
+	case *types2.Slice:
+		return types.NewSlice(g.typ(typ.Elem()))
+
+	case *types2.Struct:
+		fields := make([]*types.Field, typ.NumFields())
+		for i := range fields {
+			v := typ.Field(i)
+			f := types.NewField(g.pos(v), g.selector(v), g.typ(v.Type()))
+			f.Note = typ.Tag(i)
+			if v.Embedded() {
+				f.Embedded = 1
+			}
+			fields[i] = f
+		}
+		return types.NewStruct(g.tpkg(typ), fields)
+
+	case *types2.Interface:
+		embeddeds := make([]*types.Field, typ.NumEmbeddeds())
+		for i := range embeddeds {
+			// TODO(mdempsky): Get embedding position.
+			e := typ.EmbeddedType(i)
+			embeddeds[i] = types.NewField(src.NoXPos, nil, g.typ(e))
+		}
+
+		methods := make([]*types.Field, typ.NumExplicitMethods())
+		for i := range methods {
+			m := typ.ExplicitMethod(i)
+			mtyp := g.signature(typecheck.FakeRecv(), m.Type().(*types2.Signature))
+			methods[i] = types.NewField(g.pos(m), g.selector(m), mtyp)
+		}
+
+		return types.NewInterface(g.tpkg(typ), append(embeddeds, methods...))
+
+	default:
+		base.FatalfAt(src.NoXPos, "unhandled type: %v (%T)", typ, typ)
+		panic("unreachable")
+	}
+}
+
+func (g *irgen) signature(recv *types.Field, sig *types2.Signature) *types.Type {
+	do := func(typ *types2.Tuple) []*types.Field {
+		fields := make([]*types.Field, typ.Len())
+		for i := range fields {
+			fields[i] = g.param(typ.At(i))
+		}
+		return fields
+	}
+
+	params := do(sig.Params())
+	results := do(sig.Results())
+	if sig.Variadic() {
+		params[len(params)-1].SetIsDDD(true)
+	}
+
+	return types.NewSignature(g.tpkg(sig), recv, params, results)
+}
+
+func (g *irgen) param(v *types2.Var) *types.Field {
+	return types.NewField(g.pos(v), g.sym(v), g.typ(v.Type()))
+}
+
+func (g *irgen) sym(obj types2.Object) *types.Sym {
+	if name := obj.Name(); name != "" {
+		return g.pkg(obj.Pkg()).Lookup(obj.Name())
+	}
+	return nil
+}
+
+func (g *irgen) selector(obj types2.Object) *types.Sym {
+	pkg, name := g.pkg(obj.Pkg()), obj.Name()
+	if types.IsExported(name) {
+		pkg = types.LocalPkg
+	}
+	return pkg.Lookup(name)
+}
+
+// tpkg returns the package that a function, interface, or struct type
+// expression appeared in.
+//
+// Caveat: For the degenerate types "func()", "interface{}", and
+// "struct{}", tpkg always returns LocalPkg. However, we only need the
+// package information so that go/types can report it via its API, and
+// the reason we fail to return the original package for these
+// particular types is because go/types does *not* report it for
+// them. So in practice this limitation is probably moot.
+func (g *irgen) tpkg(typ types2.Type) *types.Pkg {
+	anyObj := func() types2.Object {
+		switch typ := typ.(type) {
+		case *types2.Signature:
+			if recv := typ.Recv(); recv != nil {
+				return recv
+			}
+			if params := typ.Params(); params.Len() > 0 {
+				return params.At(0)
+			}
+			if results := typ.Results(); results.Len() > 0 {
+				return results.At(0)
+			}
+		case *types2.Struct:
+			if typ.NumFields() > 0 {
+				return typ.Field(0)
+			}
+		case *types2.Interface:
+			if typ.NumExplicitMethods() > 0 {
+				return typ.ExplicitMethod(0)
+			}
+		}
+		return nil
+	}
+
+	if obj := anyObj(); obj != nil {
+		return g.pkg(obj.Pkg())
+	}
+	return types.LocalPkg
+}
+
+func (g *irgen) basic(typ *types2.Basic) *types.Type {
+	switch typ.Name() {
+	case "byte":
+		return types.ByteType
+	case "rune":
+		return types.RuneType
+	}
+	return *basics[typ.Kind()]
+}
+
+var basics = [...]**types.Type{
+	types2.Invalid:        new(*types.Type),
+	types2.Bool:           &types.Types[types.TBOOL],
+	types2.Int:            &types.Types[types.TINT],
+	types2.Int8:           &types.Types[types.TINT8],
+	types2.Int16:          &types.Types[types.TINT16],
+	types2.Int32:          &types.Types[types.TINT32],
+	types2.Int64:          &types.Types[types.TINT64],
+	types2.Uint:           &types.Types[types.TUINT],
+	types2.Uint8:          &types.Types[types.TUINT8],
+	types2.Uint16:         &types.Types[types.TUINT16],
+	types2.Uint32:         &types.Types[types.TUINT32],
+	types2.Uint64:         &types.Types[types.TUINT64],
+	types2.Uintptr:        &types.Types[types.TUINTPTR],
+	types2.Float32:        &types.Types[types.TFLOAT32],
+	types2.Float64:        &types.Types[types.TFLOAT64],
+	types2.Complex64:      &types.Types[types.TCOMPLEX64],
+	types2.Complex128:     &types.Types[types.TCOMPLEX128],
+	types2.String:         &types.Types[types.TSTRING],
+	types2.UnsafePointer:  &types.Types[types.TUNSAFEPTR],
+	types2.UntypedBool:    &types.UntypedBool,
+	types2.UntypedInt:     &types.UntypedInt,
+	types2.UntypedRune:    &types.UntypedRune,
+	types2.UntypedFloat:   &types.UntypedFloat,
+	types2.UntypedComplex: &types.UntypedComplex,
+	types2.UntypedString:  &types.UntypedString,
+	types2.UntypedNil:     &types.Types[types.TNIL],
+}
+
+var dirs = [...]types.ChanDir{
+	types2.SendRecv: types.Cboth,
+	types2.SendOnly: types.Csend,
+	types2.RecvOnly: types.Crecv,
+}

src/cmd/compile/internal/noder/validate.go

@@ -0,0 +1,113 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"go/constant"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+)
+
+// match reports whether types t1 and t2 are consistent
+// representations for a given expression's type.
+func (g *irgen) match(t1 *types.Type, t2 types2.Type, hasOK bool) bool {
+	tuple, ok := t2.(*types2.Tuple)
+	if !ok {
+		// Not a tuple; can use simple type identity comparison.
+		return types.Identical(t1, g.typ(t2))
+	}
+
+	if hasOK {
+		// For has-ok values, types2 represents the expression's type as
+		// a 2-element tuple, whereas ir just uses the first type and
+		// infers that the second type is boolean.
+		return tuple.Len() == 2 && types.Identical(t1, g.typ(tuple.At(0).Type()))
+	}
+
+	if t1 == nil || tuple == nil {
+		return t1 == nil && tuple == nil
+	}
+	if !t1.IsFuncArgStruct() {
+		return false
+	}
+	if t1.NumFields() != tuple.Len() {
+		return false
+	}
+	for i, result := range t1.FieldSlice() {
+		if !types.Identical(result.Type, g.typ(tuple.At(i).Type())) {
+			return false
+		}
+	}
+	return true
+}
+
+func (g *irgen) validate(n syntax.Node) {
+	switch n := n.(type) {
+	case *syntax.CallExpr:
+		tv := g.info.Types[n.Fun]
+		if tv.IsBuiltin() {
+			switch builtin := n.Fun.(type) {
+			case *syntax.Name:
+				g.validateBuiltin(builtin.Value, n)
+			case *syntax.SelectorExpr:
+				g.validateBuiltin(builtin.Sel.Value, n)
+			default:
+				g.unhandled("builtin", n)
+			}
+		}
+	}
+}
+
+func (g *irgen) validateBuiltin(name string, call *syntax.CallExpr) {
+	switch name {
+	case "Alignof", "Offsetof", "Sizeof":
+		// Check that types2+gcSizes calculates sizes the same
+		// as cmd/compile does.
+
+		got, ok := constant.Int64Val(g.info.Types[call].Value)
+		if !ok {
+			base.FatalfAt(g.pos(call), "expected int64 constant value")
+		}
+
+		want := g.unsafeExpr(name, call.ArgList[0])
+		if got != want {
+			base.FatalfAt(g.pos(call), "got %v from types2, but want %v", got, want)
+		}
+	}
+}
+
+// unsafeExpr evaluates the given unsafe builtin function on arg.
+func (g *irgen) unsafeExpr(name string, arg syntax.Expr) int64 {
+	switch name {
+	case "Alignof":
+		return g.typ(g.info.Types[arg].Type).Alignment()
+	case "Sizeof":
+		return g.typ(g.info.Types[arg].Type).Size()
+	}
+
+	// Offsetof
+
+	sel := arg.(*syntax.SelectorExpr)
+	selection := g.info.Selections[sel]
+
+	typ := g.typ(g.info.Types[sel.X].Type)
+	if typ.IsPtr() {
+		typ = typ.Elem()
+	}
+
+	var offset int64
+	for _, i := range selection.Index() {
+		// Ensure field offsets have been calculated.
+		types.CalcSize(typ)
+
+		f := typ.Field(i)
+		offset += f.Offset
+		typ = f.Type
+	}
+	return offset
+}

src/cmd/compile/internal/typecheck/dcl.go

@@ -304,10 +304,13 @@ func checkembeddedtype(t *types.Type) {
 	}
 }
 
-func fakeRecvField() *types.Field {
+// TODO(mdempsky): Move to package types.
+func FakeRecv() *types.Field {
 	return types.NewField(src.NoXPos, nil, types.FakeRecvType())
 }
 
+var fakeRecvField = FakeRecv
+
 var funcStack []funcStackEnt // stack of previous values of Curfn/dclcontext
 
 type funcStackEnt struct {

src/cmd/compile/internal/typecheck/func.go

@@ -174,7 +174,7 @@ func fnpkg(fn *ir.Name) *types.Pkg {
 
 // closurename generates a new unique name for a closure within
 // outerfunc.
-func closurename(outerfunc *ir.Func) *types.Sym {
+func ClosureName(outerfunc *ir.Func) *types.Sym {
 	outer := "glob."
 	prefix := "func"
 	gen := &globClosgen
@@ -303,7 +303,7 @@ func tcClosure(clo *ir.ClosureExpr, top int) {
 		return
 	}
 
-	fn.Nname.SetSym(closurename(ir.CurFunc))
+	fn.Nname.SetSym(ClosureName(ir.CurFunc))
 	ir.MarkFunc(fn.Nname)
 	Func(fn)
 	clo.SetType(fn.Type())

src/cmd/compile/internal/typecheck/typecheck.go

@@ -1674,10 +1674,10 @@ func CheckMapKeys() {
 	mapqueue = nil
 }
 
-// typegen tracks the number of function-scoped defined types that
+// TypeGen tracks the number of function-scoped defined types that
 // have been declared. It's used to generate unique linker symbols for
 // their runtime type descriptors.
-var typegen int32
+var TypeGen int32
 
 func typecheckdeftype(n *ir.Name) {
 	if base.EnableTrace && base.Flag.LowerT {
@@ -1686,8 +1686,8 @@ func typecheckdeftype(n *ir.Name) {
 
 	t := types.NewNamed(n)
 	if n.Curfn != nil {
-		typegen++
+		TypeGen++
-		t.Vargen = typegen
+		t.Vargen = TypeGen
 	}
 
 	if n.Pragma()&ir.NotInHeap != 0 {

src/cmd/compile/internal/types/scope.go

@@ -12,7 +12,7 @@ import (
 // Declaration stack & operations
 
 var blockgen int32 = 1 // max block number
-var Block int32        // current block number
+var Block int32 = 1    // current block number
 
 // A dsym stores a symbol's shadowed declaration so that it can be
 // restored once the block scope ends.