[dev.regabi] cmd/compile: split out package typecheck [generated]

This commit splits the typechecking logic into its own package,
the first of a sequence of CLs to break package gc into more
manageable units.

[git-generate]
cd src/cmd/compile/internal/gc
rf '
	# The binary import/export has to be part of typechecking,
	# because we load inlined function bodies lazily, but "exporter"
	# should not be. Move that out of bexport.go.
	mv exporter exporter.markObject exporter.markType export.go

	# Use the typechecking helpers, so that the calls left behind
	# in package gc do not need access to ctxExpr etc.
	ex {
		import "cmd/compile/internal/ir"

		# TODO(rsc): Should not be necessary.
		avoid TypecheckExpr
		avoid TypecheckStmt
		avoid TypecheckExprs
		avoid TypecheckStmts
		avoid TypecheckAssignExpr
		avoid TypecheckCallee

		var n ir.Node
		var ns []ir.Node
		typecheck(n, ctxExpr) -> TypecheckExpr(n)
		typecheck(n, ctxStmt) -> TypecheckStmt(n)
		typecheckslice(ns, ctxExpr) -> TypecheckExprs(ns)
		typecheckslice(ns, ctxStmt) -> TypecheckStmts(ns)
		typecheck(n, ctxExpr|ctxAssign) -> TypecheckAssignExpr(n)
		typecheck(n, ctxExpr|ctxCallee) -> TypecheckCallee(n)
	}

	# Move some typechecking API to typecheck.
	mv syslook LookupRuntime
	mv substArgTypes SubstArgTypes
	mv LookupRuntime SubstArgTypes syms.go

	mv conv Conv
	mv convnop ConvNop
	mv Conv ConvNop typecheck.go

	mv colasdefn AssignDefn
	mv colasname assignableName

	mv Target target.go

	mv initname autoexport exportsym dcl.go
	mv exportsym Export

	# Export API to be called from outside typecheck.
	# The ones with "Typecheck" prefixes will be renamed later to drop the prefix.
	mv adddot AddImplicitDots
	mv assignconv AssignConv
	mv expandmeth CalcMethods
	mv capturevarscomplete CaptureVarsComplete
	mv checkMapKeys CheckMapKeys
	mv checkreturn CheckReturn
	mv dclcontext DeclContext
	mv dclfunc DeclFunc
	mv declare Declare
	mv dotImportRefs DotImportRefs
	mv declImporter DeclImporter
	mv variter DeclVars
	mv defaultlit DefaultLit
	mv evalConst EvalConst
	mv expandInline ImportBody
	mv finishUniverse declareUniverse
	mv funcbody FinishFuncBody
	mv funchdr StartFuncBody
	mv indexconst IndexConst
	mv initTodo InitTodoFunc
	mv lookup Lookup
	mv resolve Resolve
	mv lookupN LookupNum
	mv nodAddr NodAddr
	mv nodAddrAt NodAddrAt
	mv nodnil NodNil
	mv origBoolConst OrigBool
	mv origConst OrigConst
	mv origIntConst OrigInt
	mv redeclare Redeclared
	mv tostruct NewStructType
	mv functype NewFuncType
	mv methodfunc NewMethodType
	mv structargs NewFuncParams
	mv temp Temp
	mv tempAt TempAt
	mv typecheckok TypecheckAllowed
	mv typecheck _typecheck # make room for typecheck pkg
	mv typecheckinl TypecheckImportedBody
	mv typecheckFunc TypecheckFunc
	mv iimport ReadImports
	mv iexport WriteExports
	mv sysfunc LookupRuntimeFunc
	mv sysvar LookupRuntimeVar

	# Move function constructors to typecheck.
	mv mkdotargslice MakeDotArgs
	mv fixVariadicCall FixVariadicCall
	mv closureType ClosureType
	mv partialCallType PartialCallType
	mv capturevars CaptureVars
	mv MakeDotArgs FixVariadicCall ClosureType PartialCallType CaptureVars typecheckclosure func.go

	mv autolabel AutoLabel
	mv AutoLabel syms.go

	mv Dlist dlist
	mv Symlink symlink

	mv \
		AssignDefn assignableName \
		AssignConv \
		CaptureVarsComplete \
		DeclContext \
		DeclFunc \
		DeclImporter \
		DeclVars \
		Declare \
		DotImportRefs \
		Export \
		InitTodoFunc \
		Lookup \
		LookupNum \
		LookupRuntimeFunc \
		LookupRuntimeVar \
		NewFuncParams \
		NewName \
		NodAddr \
		NodAddrAt \
		NodNil \
		Redeclared \
		StartFuncBody \
		FinishFuncBody \
		TypecheckImportedBody \
		AddImplicitDots \
		CalcMethods \
		CheckFuncStack \
		NewFuncType \
		NewMethodType \
		NewStructType \
		TypecheckAllowed \
		Temp \
		TempAt \
		adddot1 \
		dotlist \
		addmethod \
		assignconvfn \
		assignop \
		autotmpname \
		autoexport \
		bexport.go \
		checkdupfields \
		checkembeddedtype \
		closurename \
		convertop \
		declare_typegen \
		decldepth \
		dlist \
		dotpath \
		expand0 \
		expand1 \
		expandDecl \
		fakeRecvField \
		fnpkg \
		funcStack \
		funcStackEnt \
		funcarg \
		funcarg2 \
		funcargs \
		funcargs2 \
		globClosgen \
		ifacelookdot \
		implements \
		importalias \
		importconst \
		importfunc \
		importobj \
		importsym \
		importtype \
		importvar \
		inimport \
		initname \
		isptrto \
		loadsys \
		lookdot0 \
		lookdot1 \
		makepartialcall \
		okfor \
		okforlen \
		operandType \
		slist \
		symlink \
		tointerface \
		typeSet \
		typeSet.add \
		typeSetEntry \
		typecheckExprSwitch \
		typecheckTypeSwitch \
		typecheckpartialcall \
		typecheckrange \
		typecheckrangeExpr \
		typecheckselect \
		typecheckswitch \
		vargen \
		builtin.go \
		builtin_test.go \
		const.go \
		func.go \
		iexport.go \
		iimport.go \
		mapfile_mmap.go \
		syms.go \
		target.go \
		typecheck.go \
		unsafe.go \
		universe.go \
		cmd/compile/internal/typecheck
'
rm gen.go types.go types_acc.go

sed -i '' 's/package gc/package typecheck/' mapfile_read.go mkbuiltin.go
mv mapfile_read.go ../typecheck # not part of default build
mv mkbuiltin.go ../typecheck # package main helper
mv builtin ../typecheck

cd ../typecheck
mv dcl.go dcl1.go
mv typecheck.go typecheck1.go
mv universe.go universe1.go
rf '
	# Sweep some small files into larger ones.
	# "mv sym... file1.go file.go" (after the mv file1.go file.go above)
	# lets us insert sym... at the top of file.go.
	mv okfor okforeq universe1.go universe.go
	mv DeclContext vargen dcl1.go Temp TempAt autotmpname NewMethodType dcl.go
	mv InitTodoFunc inimport decldepth TypecheckAllowed typecheck1.go typecheck.go
	mv inl.go closure.go func.go
	mv range.go select.go swt.go stmt.go
	mv Lookup loadsys LookupRuntimeFunc LookupRuntimeVar syms.go
	mv unsafe.go const.go

	mv TypecheckAssignExpr AssignExpr
	mv TypecheckExpr Expr
	mv TypecheckStmt Stmt
	mv TypecheckExprs Exprs
	mv TypecheckStmts Stmts
	mv TypecheckCall Call
	mv TypecheckCallee Callee
	mv _typecheck check
	mv TypecheckFunc Func
	mv TypecheckFuncBody FuncBody
	mv TypecheckImports AllImportedBodies
	mv TypecheckImportedBody ImportedBody
	mv TypecheckInit Init
	mv TypecheckPackage Package
'
rm gen.go go.go init.go main.go reflect.go

Change-Id: Iea6a7aaf6407d690670ec58aeb36cc0b280f80b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/279236
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 793 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
new file mode 100644
index 0000000000..22ebf2a4b3
--- /dev/null
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -0,0 +1,793 @@
+// Copyright 2009 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 typecheck
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+)
+
+func AssignConv(n ir.Node, t *types.Type, context string) ir.Node {
+	return assignconvfn(n, t, func() string { return context })
+}
+
+// DotImportRefs maps idents introduced by importDot back to the
+// ir.PkgName they were dot-imported through.
+var DotImportRefs map[*ir.Ident]*ir.PkgName
+
+// LookupNum looks up the symbol starting with prefix and ending with
+// the decimal n. If prefix is too long, LookupNum panics.
+func LookupNum(prefix string, n int) *types.Sym {
+	var buf [20]byte // plenty long enough for all current users
+	copy(buf[:], prefix)
+	b := strconv.AppendInt(buf[:len(prefix)], int64(n), 10)
+	return types.LocalPkg.LookupBytes(b)
+}
+
+// Given funarg struct list, return list of fn args.
+func NewFuncParams(tl *types.Type, mustname bool) []*ir.Field {
+	var args []*ir.Field
+	gen := 0
+	for _, t := range tl.Fields().Slice() {
+		s := t.Sym
+		if mustname && (s == nil || s.Name == "_") {
+			// invent a name so that we can refer to it in the trampoline
+			s = LookupNum(".anon", gen)
+			gen++
+		}
+		a := ir.NewField(base.Pos, s, nil, t.Type)
+		a.Pos = t.Pos
+		a.IsDDD = t.IsDDD()
+		args = append(args, a)
+	}
+
+	return args
+}
+
+// newname returns a new ONAME Node associated with symbol s.
+func NewName(s *types.Sym) *ir.Name {
+	n := ir.NewNameAt(base.Pos, s)
+	n.Curfn = ir.CurFunc
+	return n
+}
+
+// NodAddr returns a node representing &n at base.Pos.
+func NodAddr(n ir.Node) *ir.AddrExpr {
+	return NodAddrAt(base.Pos, n)
+}
+
+// nodAddrPos returns a node representing &n at position pos.
+func NodAddrAt(pos src.XPos, n ir.Node) *ir.AddrExpr {
+	return ir.NewAddrExpr(pos, n)
+}
+
+func NodNil() ir.Node {
+	n := ir.NewNilExpr(base.Pos)
+	n.SetType(types.Types[types.TNIL])
+	return n
+}
+
+// in T.field
+// find missing fields that
+// will give shortest unique addressing.
+// modify the tree with missing type names.
+func AddImplicitDots(n *ir.SelectorExpr) *ir.SelectorExpr {
+	n.X = check(n.X, ctxType|ctxExpr)
+	if n.X.Diag() {
+		n.SetDiag(true)
+	}
+	t := n.X.Type()
+	if t == nil {
+		return n
+	}
+
+	if n.X.Op() == ir.OTYPE {
+		return n
+	}
+
+	s := n.Sel
+	if s == nil {
+		return n
+	}
+
+	switch path, ambig := dotpath(s, t, nil, false); {
+	case path != nil:
+		// rebuild elided dots
+		for c := len(path) - 1; c >= 0; c-- {
+			dot := ir.NewSelectorExpr(base.Pos, ir.ODOT, n.X, path[c].field.Sym)
+			dot.SetImplicit(true)
+			dot.SetType(path[c].field.Type)
+			n.X = dot
+		}
+	case ambig:
+		base.Errorf("ambiguous selector %v", n)
+		n.X = nil
+	}
+
+	return n
+}
+
+func CalcMethods(t *types.Type) {
+	if t == nil || t.AllMethods().Len() != 0 {
+		return
+	}
+
+	// mark top-level method symbols
+	// so that expand1 doesn't consider them.
+	for _, f := range t.Methods().Slice() {
+		f.Sym.SetUniq(true)
+	}
+
+	// generate all reachable methods
+	slist = slist[:0]
+	expand1(t, true)
+
+	// check each method to be uniquely reachable
+	var ms []*types.Field
+	for i, sl := range slist {
+		slist[i].field = nil
+		sl.field.Sym.SetUniq(false)
+
+		var f *types.Field
+		path, _ := dotpath(sl.field.Sym, t, &f, false)
+		if path == nil {
+			continue
+		}
+
+		// dotpath may have dug out arbitrary fields, we only want methods.
+		if !f.IsMethod() {
+			continue
+		}
+
+		// add it to the base type method list
+		f = f.Copy()
+		f.Embedded = 1 // needs a trampoline
+		for _, d := range path {
+			if d.field.Type.IsPtr() {
+				f.Embedded = 2
+				break
+			}
+		}
+		ms = append(ms, f)
+	}
+
+	for _, f := range t.Methods().Slice() {
+		f.Sym.SetUniq(false)
+	}
+
+	ms = append(ms, t.Methods().Slice()...)
+	sort.Sort(types.MethodsByName(ms))
+	t.AllMethods().Set(ms)
+}
+
+// adddot1 returns the number of fields or methods named s at depth d in Type t.
+// If exactly one exists, it will be returned in *save (if save is not nil),
+// and dotlist will contain the path of embedded fields traversed to find it,
+// in reverse order. If none exist, more will indicate whether t contains any
+// embedded fields at depth d, so callers can decide whether to retry at
+// a greater depth.
+func adddot1(s *types.Sym, t *types.Type, d int, save **types.Field, ignorecase bool) (c int, more bool) {
+	if t.Recur() {
+		return
+	}
+	t.SetRecur(true)
+	defer t.SetRecur(false)
+
+	var u *types.Type
+	d--
+	if d < 0 {
+		// We've reached our target depth. If t has any fields/methods
+		// named s, then we're done. Otherwise, we still need to check
+		// below for embedded fields.
+		c = lookdot0(s, t, save, ignorecase)
+		if c != 0 {
+			return c, false
+		}
+	}
+
+	u = t
+	if u.IsPtr() {
+		u = u.Elem()
+	}
+	if !u.IsStruct() && !u.IsInterface() {
+		return c, false
+	}
+
+	for _, f := range u.Fields().Slice() {
+		if f.Embedded == 0 || f.Sym == nil {
+			continue
+		}
+		if d < 0 {
+			// Found an embedded field at target depth.
+			return c, true
+		}
+		a, more1 := adddot1(s, f.Type, d, save, ignorecase)
+		if a != 0 && c == 0 {
+			dotlist[d].field = f
+		}
+		c += a
+		if more1 {
+			more = true
+		}
+	}
+
+	return c, more
+}
+
+// dotlist is used by adddot1 to record the path of embedded fields
+// used to access a target field or method.
+// Must be non-nil so that dotpath returns a non-nil slice even if d is zero.
+var dotlist = make([]dlist, 10)
+
+// Convert node n for assignment to type t.
+func assignconvfn(n ir.Node, t *types.Type, context func() string) ir.Node {
+	if n == nil || n.Type() == nil || n.Type().Broke() {
+		return n
+	}
+
+	if t.Kind() == types.TBLANK && n.Type().Kind() == types.TNIL {
+		base.Errorf("use of untyped nil")
+	}
+
+	n = convlit1(n, t, false, context)
+	if n.Type() == nil {
+		return n
+	}
+	if t.Kind() == types.TBLANK {
+		return n
+	}
+
+	// Convert ideal bool from comparison to plain bool
+	// if the next step is non-bool (like interface{}).
+	if n.Type() == types.UntypedBool && !t.IsBoolean() {
+		if n.Op() == ir.ONAME || n.Op() == ir.OLITERAL {
+			r := ir.NewConvExpr(base.Pos, ir.OCONVNOP, nil, n)
+			r.SetType(types.Types[types.TBOOL])
+			r.SetTypecheck(1)
+			r.SetImplicit(true)
+			n = r
+		}
+	}
+
+	if types.Identical(n.Type(), t) {
+		return n
+	}
+
+	op, why := assignop(n.Type(), t)
+	if op == ir.OXXX {
+		base.Errorf("cannot use %L as type %v in %s%s", n, t, context(), why)
+		op = ir.OCONV
+	}
+
+	r := ir.NewConvExpr(base.Pos, op, t, n)
+	r.SetTypecheck(1)
+	r.SetImplicit(true)
+	return r
+}
+
+// Is type src assignment compatible to type dst?
+// If so, return op code to use in conversion.
+// If not, return OXXX. In this case, the string return parameter may
+// hold a reason why. In all other cases, it'll be the empty string.
+func assignop(src, dst *types.Type) (ir.Op, string) {
+	if src == dst {
+		return ir.OCONVNOP, ""
+	}
+	if src == nil || dst == nil || src.Kind() == types.TFORW || dst.Kind() == types.TFORW || src.Underlying() == nil || dst.Underlying() == nil {
+		return ir.OXXX, ""
+	}
+
+	// 1. src type is identical to dst.
+	if types.Identical(src, dst) {
+		return ir.OCONVNOP, ""
+	}
+
+	// 2. src and dst have identical underlying types
+	// and either src or dst is not a named type or
+	// both are empty interface types.
+	// For assignable but different non-empty interface types,
+	// we want to recompute the itab. Recomputing the itab ensures
+	// that itabs are unique (thus an interface with a compile-time
+	// type I has an itab with interface type I).
+	if types.Identical(src.Underlying(), dst.Underlying()) {
+		if src.IsEmptyInterface() {
+			// Conversion between two empty interfaces
+			// requires no code.
+			return ir.OCONVNOP, ""
+		}
+		if (src.Sym() == nil || dst.Sym() == nil) && !src.IsInterface() {
+			// Conversion between two types, at least one unnamed,
+			// needs no conversion. The exception is nonempty interfaces
+			// which need to have their itab updated.
+			return ir.OCONVNOP, ""
+		}
+	}
+
+	// 3. dst is an interface type and src implements dst.
+	if dst.IsInterface() && src.Kind() != types.TNIL {
+		var missing, have *types.Field
+		var ptr int
+		if implements(src, dst, &missing, &have, &ptr) {
+			// Call itabname so that (src, dst)
+			// gets added to itabs early, which allows
+			// us to de-virtualize calls through this
+			// type/interface pair later. See peekitabs in reflect.go
+			if types.IsDirectIface(src) && !dst.IsEmptyInterface() {
+				NeedITab(src, dst)
+			}
+
+			return ir.OCONVIFACE, ""
+		}
+
+		// we'll have complained about this method anyway, suppress spurious messages.
+		if have != nil && have.Sym == missing.Sym && (have.Type.Broke() || missing.Type.Broke()) {
+			return ir.OCONVIFACE, ""
+		}
+
+		var why string
+		if isptrto(src, types.TINTER) {
+			why = fmt.Sprintf(":\n\t%v is pointer to interface, not interface", src)
+		} else if have != nil && have.Sym == missing.Sym && have.Nointerface() {
+			why = fmt.Sprintf(":\n\t%v does not implement %v (%v method is marked 'nointerface')", src, dst, missing.Sym)
+		} else if have != nil && have.Sym == missing.Sym {
+			why = fmt.Sprintf(":\n\t%v does not implement %v (wrong type for %v method)\n"+
+				"\t\thave %v%S\n\t\twant %v%S", src, dst, missing.Sym, have.Sym, have.Type, missing.Sym, missing.Type)
+		} else if ptr != 0 {
+			why = fmt.Sprintf(":\n\t%v does not implement %v (%v method has pointer receiver)", src, dst, missing.Sym)
+		} else if have != nil {
+			why = fmt.Sprintf(":\n\t%v does not implement %v (missing %v method)\n"+
+				"\t\thave %v%S\n\t\twant %v%S", src, dst, missing.Sym, have.Sym, have.Type, missing.Sym, missing.Type)
+		} else {
+			why = fmt.Sprintf(":\n\t%v does not implement %v (missing %v method)", src, dst, missing.Sym)
+		}
+
+		return ir.OXXX, why
+	}
+
+	if isptrto(dst, types.TINTER) {
+		why := fmt.Sprintf(":\n\t%v is pointer to interface, not interface", dst)
+		return ir.OXXX, why
+	}
+
+	if src.IsInterface() && dst.Kind() != types.TBLANK {
+		var missing, have *types.Field
+		var ptr int
+		var why string
+		if implements(dst, src, &missing, &have, &ptr) {
+			why = ": need type assertion"
+		}
+		return ir.OXXX, why
+	}
+
+	// 4. src is a bidirectional channel value, dst is a channel type,
+	// src and dst have identical element types, and
+	// either src or dst is not a named type.
+	if src.IsChan() && src.ChanDir() == types.Cboth && dst.IsChan() {
+		if types.Identical(src.Elem(), dst.Elem()) && (src.Sym() == nil || dst.Sym() == nil) {
+			return ir.OCONVNOP, ""
+		}
+	}
+
+	// 5. src is the predeclared identifier nil and dst is a nillable type.
+	if src.Kind() == types.TNIL {
+		switch dst.Kind() {
+		case types.TPTR,
+			types.TFUNC,
+			types.TMAP,
+			types.TCHAN,
+			types.TINTER,
+			types.TSLICE:
+			return ir.OCONVNOP, ""
+		}
+	}
+
+	// 6. rule about untyped constants - already converted by defaultlit.
+
+	// 7. Any typed value can be assigned to the blank identifier.
+	if dst.Kind() == types.TBLANK {
+		return ir.OCONVNOP, ""
+	}
+
+	return ir.OXXX, ""
+}
+
+// Can we convert a value of type src to a value of type dst?
+// If so, return op code to use in conversion (maybe OCONVNOP).
+// If not, return OXXX. In this case, the string return parameter may
+// hold a reason why. In all other cases, it'll be the empty string.
+// srcConstant indicates whether the value of type src is a constant.
+func convertop(srcConstant bool, src, dst *types.Type) (ir.Op, string) {
+	if src == dst {
+		return ir.OCONVNOP, ""
+	}
+	if src == nil || dst == nil {
+		return ir.OXXX, ""
+	}
+
+	// Conversions from regular to go:notinheap are not allowed
+	// (unless it's unsafe.Pointer). These are runtime-specific
+	// rules.
+	// (a) Disallow (*T) to (*U) where T is go:notinheap but U isn't.
+	if src.IsPtr() && dst.IsPtr() && dst.Elem().NotInHeap() && !src.Elem().NotInHeap() {
+		why := fmt.Sprintf(":\n\t%v is incomplete (or unallocatable), but %v is not", dst.Elem(), src.Elem())
+		return ir.OXXX, why
+	}
+	// (b) Disallow string to []T where T is go:notinheap.
+	if src.IsString() && dst.IsSlice() && dst.Elem().NotInHeap() && (dst.Elem().Kind() == types.ByteType.Kind() || dst.Elem().Kind() == types.RuneType.Kind()) {
+		why := fmt.Sprintf(":\n\t%v is incomplete (or unallocatable)", dst.Elem())
+		return ir.OXXX, why
+	}
+
+	// 1. src can be assigned to dst.
+	op, why := assignop(src, dst)
+	if op != ir.OXXX {
+		return op, why
+	}
+
+	// The rules for interfaces are no different in conversions
+	// than assignments. If interfaces are involved, stop now
+	// with the good message from assignop.
+	// Otherwise clear the error.
+	if src.IsInterface() || dst.IsInterface() {
+		return ir.OXXX, why
+	}
+
+	// 2. Ignoring struct tags, src and dst have identical underlying types.
+	if types.IdenticalIgnoreTags(src.Underlying(), dst.Underlying()) {
+		return ir.OCONVNOP, ""
+	}
+
+	// 3. src and dst are unnamed pointer types and, ignoring struct tags,
+	// their base types have identical underlying types.
+	if src.IsPtr() && dst.IsPtr() && src.Sym() == nil && dst.Sym() == nil {
+		if types.IdenticalIgnoreTags(src.Elem().Underlying(), dst.Elem().Underlying()) {
+			return ir.OCONVNOP, ""
+		}
+	}
+
+	// 4. src and dst are both integer or floating point types.
+	if (src.IsInteger() || src.IsFloat()) && (dst.IsInteger() || dst.IsFloat()) {
+		if types.SimType[src.Kind()] == types.SimType[dst.Kind()] {
+			return ir.OCONVNOP, ""
+		}
+		return ir.OCONV, ""
+	}
+
+	// 5. src and dst are both complex types.
+	if src.IsComplex() && dst.IsComplex() {
+		if types.SimType[src.Kind()] == types.SimType[dst.Kind()] {
+			return ir.OCONVNOP, ""
+		}
+		return ir.OCONV, ""
+	}
+
+	// Special case for constant conversions: any numeric
+	// conversion is potentially okay. We'll validate further
+	// within evconst. See #38117.
+	if srcConstant && (src.IsInteger() || src.IsFloat() || src.IsComplex()) && (dst.IsInteger() || dst.IsFloat() || dst.IsComplex()) {
+		return ir.OCONV, ""
+	}
+
+	// 6. src is an integer or has type []byte or []rune
+	// and dst is a string type.
+	if src.IsInteger() && dst.IsString() {
+		return ir.ORUNESTR, ""
+	}
+
+	if src.IsSlice() && dst.IsString() {
+		if src.Elem().Kind() == types.ByteType.Kind() {
+			return ir.OBYTES2STR, ""
+		}
+		if src.Elem().Kind() == types.RuneType.Kind() {
+			return ir.ORUNES2STR, ""
+		}
+	}
+
+	// 7. src is a string and dst is []byte or []rune.
+	// String to slice.
+	if src.IsString() && dst.IsSlice() {
+		if dst.Elem().Kind() == types.ByteType.Kind() {
+			return ir.OSTR2BYTES, ""
+		}
+		if dst.Elem().Kind() == types.RuneType.Kind() {
+			return ir.OSTR2RUNES, ""
+		}
+	}
+
+	// 8. src is a pointer or uintptr and dst is unsafe.Pointer.
+	if (src.IsPtr() || src.IsUintptr()) && dst.IsUnsafePtr() {
+		return ir.OCONVNOP, ""
+	}
+
+	// 9. src is unsafe.Pointer and dst is a pointer or uintptr.
+	if src.IsUnsafePtr() && (dst.IsPtr() || dst.IsUintptr()) {
+		return ir.OCONVNOP, ""
+	}
+
+	// src is map and dst is a pointer to corresponding hmap.
+	// This rule is needed for the implementation detail that
+	// go gc maps are implemented as a pointer to a hmap struct.
+	if src.Kind() == types.TMAP && dst.IsPtr() &&
+		src.MapType().Hmap == dst.Elem() {
+		return ir.OCONVNOP, ""
+	}
+
+	return ir.OXXX, ""
+}
+
+// Code to resolve elided DOTs in embedded types.
+
+// A dlist stores a pointer to a TFIELD Type embedded within
+// a TSTRUCT or TINTER Type.
+type dlist struct {
+	field *types.Field
+}
+
+// dotpath computes the unique shortest explicit selector path to fully qualify
+// a selection expression x.f, where x is of type t and f is the symbol s.
+// If no such path exists, dotpath returns nil.
+// If there are multiple shortest paths to the same depth, ambig is true.
+func dotpath(s *types.Sym, t *types.Type, save **types.Field, ignorecase bool) (path []dlist, ambig bool) {
+	// The embedding of types within structs imposes a tree structure onto
+	// types: structs parent the types they embed, and types parent their
+	// fields or methods. Our goal here is to find the shortest path to
+	// a field or method named s in the subtree rooted at t. To accomplish
+	// that, we iteratively perform depth-first searches of increasing depth
+	// until we either find the named field/method or exhaust the tree.
+	for d := 0; ; d++ {
+		if d > len(dotlist) {
+			dotlist = append(dotlist, dlist{})
+		}
+		if c, more := adddot1(s, t, d, save, ignorecase); c == 1 {
+			return dotlist[:d], false
+		} else if c > 1 {
+			return nil, true
+		} else if !more {
+			return nil, false
+		}
+	}
+}
+
+func expand0(t *types.Type) {
+	u := t
+	if u.IsPtr() {
+		u = u.Elem()
+	}
+
+	if u.IsInterface() {
+		for _, f := range u.Fields().Slice() {
+			if f.Sym.Uniq() {
+				continue
+			}
+			f.Sym.SetUniq(true)
+			slist = append(slist, symlink{field: f})
+		}
+
+		return
+	}
+
+	u = types.ReceiverBaseType(t)
+	if u != nil {
+		for _, f := range u.Methods().Slice() {
+			if f.Sym.Uniq() {
+				continue
+			}
+			f.Sym.SetUniq(true)
+			slist = append(slist, symlink{field: f})
+		}
+	}
+}
+
+func expand1(t *types.Type, top bool) {
+	if t.Recur() {
+		return
+	}
+	t.SetRecur(true)
+
+	if !top {
+		expand0(t)
+	}
+
+	u := t
+	if u.IsPtr() {
+		u = u.Elem()
+	}
+
+	if u.IsStruct() || u.IsInterface() {
+		for _, f := range u.Fields().Slice() {
+			if f.Embedded == 0 {
+				continue
+			}
+			if f.Sym == nil {
+				continue
+			}
+			expand1(f.Type, false)
+		}
+	}
+
+	t.SetRecur(false)
+}
+
+func ifacelookdot(s *types.Sym, t *types.Type, ignorecase bool) (m *types.Field, followptr bool) {
+	if t == nil {
+		return nil, false
+	}
+
+	path, ambig := dotpath(s, t, &m, ignorecase)
+	if path == nil {
+		if ambig {
+			base.Errorf("%v.%v is ambiguous", t, s)
+		}
+		return nil, false
+	}
+
+	for _, d := range path {
+		if d.field.Type.IsPtr() {
+			followptr = true
+			break
+		}
+	}
+
+	if !m.IsMethod() {
+		base.Errorf("%v.%v is a field, not a method", t, s)
+		return nil, followptr
+	}
+
+	return m, followptr
+}
+
+func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool {
+	t0 := t
+	if t == nil {
+		return false
+	}
+
+	if t.IsInterface() {
+		i := 0
+		tms := t.Fields().Slice()
+		for _, im := range iface.Fields().Slice() {
+			for i < len(tms) && tms[i].Sym != im.Sym {
+				i++
+			}
+			if i == len(tms) {
+				*m = im
+				*samename = nil
+				*ptr = 0
+				return false
+			}
+			tm := tms[i]
+			if !types.Identical(tm.Type, im.Type) {
+				*m = im
+				*samename = tm
+				*ptr = 0
+				return false
+			}
+		}
+
+		return true
+	}
+
+	t = types.ReceiverBaseType(t)
+	var tms []*types.Field
+	if t != nil {
+		CalcMethods(t)
+		tms = t.AllMethods().Slice()
+	}
+	i := 0
+	for _, im := range iface.Fields().Slice() {
+		if im.Broke() {
+			continue
+		}
+		for i < len(tms) && tms[i].Sym != im.Sym {
+			i++
+		}
+		if i == len(tms) {
+			*m = im
+			*samename, _ = ifacelookdot(im.Sym, t, true)
+			*ptr = 0
+			return false
+		}
+		tm := tms[i]
+		if tm.Nointerface() || !types.Identical(tm.Type, im.Type) {
+			*m = im
+			*samename = tm
+			*ptr = 0
+			return false
+		}
+		followptr := tm.Embedded == 2
+
+		// if pointer receiver in method,
+		// the method does not exist for value types.
+		rcvr := tm.Type.Recv().Type
+		if rcvr.IsPtr() && !t0.IsPtr() && !followptr && !types.IsInterfaceMethod(tm.Type) {
+			if false && base.Flag.LowerR != 0 {
+				base.Errorf("interface pointer mismatch")
+			}
+
+			*m = im
+			*samename = nil
+			*ptr = 1
+			return false
+		}
+	}
+
+	return true
+}
+
+func isptrto(t *types.Type, et types.Kind) bool {
+	if t == nil {
+		return false
+	}
+	if !t.IsPtr() {
+		return false
+	}
+	t = t.Elem()
+	if t == nil {
+		return false
+	}
+	if t.Kind() != et {
+		return false
+	}
+	return true
+}
+
+// lookdot0 returns the number of fields or methods named s associated
+// with Type t. If exactly one exists, it will be returned in *save
+// (if save is not nil).
+func lookdot0(s *types.Sym, t *types.Type, save **types.Field, ignorecase bool) int {
+	u := t
+	if u.IsPtr() {
+		u = u.Elem()
+	}
+
+	c := 0
+	if u.IsStruct() || u.IsInterface() {
+		for _, f := range u.Fields().Slice() {
+			if f.Sym == s || (ignorecase && f.IsMethod() && strings.EqualFold(f.Sym.Name, s.Name)) {
+				if save != nil {
+					*save = f
+				}
+				c++
+			}
+		}
+	}
+
+	u = t
+	if t.Sym() != nil && t.IsPtr() && !t.Elem().IsPtr() {
+		// If t is a defined pointer type, then x.m is shorthand for (*x).m.
+		u = t.Elem()
+	}
+	u = types.ReceiverBaseType(u)
+	if u != nil {
+		for _, f := range u.Methods().Slice() {
+			if f.Embedded == 0 && (f.Sym == s || (ignorecase && strings.EqualFold(f.Sym.Name, s.Name))) {
+				if save != nil {
+					*save = f
+				}
+				c++
+			}
+		}
+	}
+
+	return c
+}
+
+var slist []symlink
+
+// Code to help generate trampoline functions for methods on embedded
+// types. These are approx the same as the corresponding adddot
+// routines except that they expect to be called with unique tasks and
+// they return the actual methods.
+
+type symlink struct {
+	field *types.Field
+}