cmd/compile: create/use noder2 transform functions for more node types

Pull out the transformation part of the typechecking functions for:
 - assignment statements
 - return statements
 - send statements
 - select statements
 - type conversions
 - normal function/method calls
 - index operations

The transform functions are like the original typechecking functions,
but with all code removed related to:
  - Detecting compile-time errors (already done by types2)
  - Setting the actual type of existing nodes (already done based on
    info from types2)
  - Dealing with untyped constants

Moved all the transformation functions to a separate file, transform.go.

Continuing with the same pattern, we delay transforming a node if it has
any type params in its args, marking it with a typecheck flag of 3, and
do the actual transformation during stenciling.

Assignment statements are tricky, since their transformation must be
delayed if any of the left or right-hands-sides are delayed.

Still to do are:
 - selector expressions (OXDOT)
 - composite literal expressions (OCOMPLIT)
 - builtin function calls

Change-Id: Ie608cadbbc69b40db0067a5536cf707dd974aacc
Reviewed-on: https://go-review.googlesource.com/c/go/+/304049
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -0,0 +1,523 @@
+// 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.
+
+// This file contains transformation functions on nodes, which are the
+// transformations that the typecheck package does that are distinct from the
+// typechecking functionality. These transform functions are pared-down copies of
+// the original typechecking functions, with all code removed that is related to:
+//
+//    - Detecting compile-time errors (already done by types2)
+//    - Setting the actual type of existing nodes (already done based on
+//      type info from types2)
+//    - Dealing with untyped constants (which types2 has already resolved)
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"go/constant"
+)
+
+// Transformation functions for expressions
+
+// transformAdd transforms an addition operation (currently just addition of
+// strings). Corresponds to the "binary operators" case in typecheck.typecheck1.
+func transformAdd(n *ir.BinaryExpr) ir.Node {
+	l := n.X
+	if l.Type().IsString() {
+		var add *ir.AddStringExpr
+		if l.Op() == ir.OADDSTR {
+			add = l.(*ir.AddStringExpr)
+			add.SetPos(n.Pos())
+		} else {
+			add = ir.NewAddStringExpr(n.Pos(), []ir.Node{l})
+		}
+		r := n.Y
+		if r.Op() == ir.OADDSTR {
+			r := r.(*ir.AddStringExpr)
+			add.List.Append(r.List.Take()...)
+		} else {
+			add.List.Append(r)
+		}
+		add.SetType(l.Type())
+		return add
+	}
+	return n
+}
+
+// Corresponds to typecheck.stringtoruneslit.
+func stringtoruneslit(n *ir.ConvExpr) ir.Node {
+	if n.X.Op() != ir.OLITERAL || n.X.Val().Kind() != constant.String {
+		base.Fatalf("stringtoarraylit %v", n)
+	}
+
+	var l []ir.Node
+	i := 0
+	for _, r := range ir.StringVal(n.X) {
+		l = append(l, ir.NewKeyExpr(base.Pos, ir.NewInt(int64(i)), ir.NewInt(int64(r))))
+		i++
+	}
+
+	nn := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, ir.TypeNode(n.Type()), nil)
+	nn.List = l
+	// Need to transform the OCOMPLIT.
+	// TODO(danscales): update this when we have written transformCompLit()
+	return typecheck.Expr(nn)
+}
+
+// transformConv transforms an OCONV node as needed, based on the types involved,
+// etc.  Corresponds to typecheck.tcConv.
+func transformConv(n *ir.ConvExpr) ir.Node {
+	t := n.X.Type()
+	op, _ := typecheck.Convertop(n.X.Op() == ir.OLITERAL, t, n.Type())
+	assert(op != ir.OXXX)
+	n.SetOp(op)
+	switch n.Op() {
+	case ir.OCONVNOP:
+		if t.Kind() == n.Type().Kind() {
+			switch t.Kind() {
+			case types.TFLOAT32, types.TFLOAT64, types.TCOMPLEX64, types.TCOMPLEX128:
+				// Floating point casts imply rounding and
+				// so the conversion must be kept.
+				n.SetOp(ir.OCONV)
+			}
+		}
+
+	// Do not convert to []byte literal. See CL 125796.
+	// Generated code and compiler memory footprint is better without it.
+	case ir.OSTR2BYTES:
+		// ok
+
+	case ir.OSTR2RUNES:
+		if n.X.Op() == ir.OLITERAL {
+			return stringtoruneslit(n)
+		}
+	}
+	return n
+}
+
+// transformConvCall transforms a conversion call. Corresponds to the OTYPE part of
+// typecheck.tcCall.
+func transformConvCall(n *ir.CallExpr) ir.Node {
+	arg := n.Args[0]
+	n1 := ir.NewConvExpr(n.Pos(), ir.OCONV, nil, arg)
+	n1.SetType(n.X.Type())
+	return transformConv(n1)
+}
+
+// transformCall transforms a normal function/method call. Corresponds to last half
+// (non-conversion, non-builtin part) of typecheck.tcCall.
+func transformCall(n *ir.CallExpr) {
+	transformArgs(n)
+	l := n.X
+	t := l.Type()
+
+	switch l.Op() {
+	case ir.ODOTINTER:
+		n.SetOp(ir.OCALLINTER)
+
+	case ir.ODOTMETH:
+		l := l.(*ir.SelectorExpr)
+		n.SetOp(ir.OCALLMETH)
+
+		tp := t.Recv().Type
+
+		if l.X == nil || !types.Identical(l.X.Type(), tp) {
+			base.Fatalf("method receiver")
+		}
+
+	default:
+		n.SetOp(ir.OCALLFUNC)
+	}
+
+	typecheckaste(ir.OCALL, n.X, n.IsDDD, t.Params(), n.Args)
+	if t.NumResults() == 0 {
+		return
+	}
+	if t.NumResults() == 1 {
+		n.SetType(l.Type().Results().Field(0).Type)
+
+		if n.Op() == ir.OCALLFUNC && n.X.Op() == ir.ONAME {
+			if sym := n.X.(*ir.Name).Sym(); types.IsRuntimePkg(sym.Pkg) && sym.Name == "getg" {
+				// Emit code for runtime.getg() directly instead of calling function.
+				// Most such rewrites (for example the similar one for math.Sqrt) should be done in walk,
+				// so that the ordering pass can make sure to preserve the semantics of the original code
+				// (in particular, the exact time of the function call) by introducing temporaries.
+				// In this case, we know getg() always returns the same result within a given function
+				// and we want to avoid the temporaries, so we do the rewrite earlier than is typical.
+				n.SetOp(ir.OGETG)
+			}
+		}
+		return
+	}
+}
+
+// transformCompare transforms a compare operation (currently just equals/not
+// equals). Corresponds to the "comparison operators" case in
+// typecheck.typecheck1, including tcArith.
+func transformCompare(n *ir.BinaryExpr) {
+	if (n.Op() == ir.OEQ || n.Op() == ir.ONE) && !types.Identical(n.X.Type(), n.Y.Type()) {
+		// Comparison is okay as long as one side is assignable to the
+		// other. The only allowed case where the conversion is not CONVNOP is
+		// "concrete == interface". In that case, check comparability of
+		// the concrete type. The conversion allocates, so only do it if
+		// the concrete type is huge.
+		l, r := n.X, n.Y
+		lt, rt := l.Type(), r.Type()
+		converted := false
+		if rt.Kind() != types.TBLANK {
+			aop, _ := typecheck.Assignop(lt, rt)
+			if aop != ir.OXXX {
+				types.CalcSize(lt)
+				if rt.IsInterface() == lt.IsInterface() || lt.Width >= 1<<16 {
+					l = ir.NewConvExpr(base.Pos, aop, rt, l)
+					l.SetTypecheck(1)
+				}
+
+				converted = true
+			}
+		}
+
+		if !converted && lt.Kind() != types.TBLANK {
+			aop, _ := typecheck.Assignop(rt, lt)
+			if aop != ir.OXXX {
+				types.CalcSize(rt)
+				if rt.IsInterface() == lt.IsInterface() || rt.Width >= 1<<16 {
+					r = ir.NewConvExpr(base.Pos, aop, lt, r)
+					r.SetTypecheck(1)
+				}
+			}
+		}
+		n.X, n.Y = l, r
+	}
+}
+
+// Corresponds to typecheck.implicitstar.
+func implicitstar(n ir.Node) ir.Node {
+	// insert implicit * if needed for fixed array
+	t := n.Type()
+	if !t.IsPtr() {
+		return n
+	}
+	t = t.Elem()
+	if !t.IsArray() {
+		return n
+	}
+	star := ir.NewStarExpr(base.Pos, n)
+	star.SetImplicit(true)
+	return typed(t, star)
+}
+
+// transformIndex transforms an index operation.  Corresponds to typecheck.tcIndex.
+func transformIndex(n *ir.IndexExpr) {
+	n.X = implicitstar(n.X)
+	l := n.X
+	t := l.Type()
+	if t.Kind() == types.TMAP {
+		n.Index = typecheck.AssignConv(n.Index, t.Key(), "map index")
+		n.SetOp(ir.OINDEXMAP)
+		// Set type to just the map value, not (value, bool). This is
+		// different from types2, but fits the later stages of the
+		// compiler better.
+		n.SetType(t.Elem())
+		n.Assigned = false
+	}
+}
+
+// transformSlice transforms a slice operation.  Corresponds to typecheck.tcSlice.
+func transformSlice(n *ir.SliceExpr) {
+	l := n.X
+	if l.Type().IsArray() {
+		addr := typecheck.NodAddr(n.X)
+		addr.SetImplicit(true)
+		typed(types.NewPtr(n.X.Type()), addr)
+		n.X = addr
+		l = addr
+	}
+	t := l.Type()
+	if t.IsString() {
+		n.SetOp(ir.OSLICESTR)
+	} else if t.IsPtr() && t.Elem().IsArray() {
+		if n.Op().IsSlice3() {
+			n.SetOp(ir.OSLICE3ARR)
+		} else {
+			n.SetOp(ir.OSLICEARR)
+		}
+	}
+}
+
+// Transformation functions for statements
+
+// Corresponds to typecheck.checkassign.
+func transformCheckAssign(stmt ir.Node, n ir.Node) {
+	if n.Op() == ir.OINDEXMAP {
+		n := n.(*ir.IndexExpr)
+		n.Assigned = true
+		return
+	}
+}
+
+// Corresponds to typecheck.assign.
+func transformAssign(stmt ir.Node, lhs, rhs []ir.Node) {
+	checkLHS := func(i int, typ *types.Type) {
+		transformCheckAssign(stmt, lhs[i])
+	}
+
+	cr := len(rhs)
+	if len(rhs) == 1 {
+		if rtyp := rhs[0].Type(); rtyp != nil && rtyp.IsFuncArgStruct() {
+			cr = rtyp.NumFields()
+		}
+	}
+
+	// x, ok = y
+assignOK:
+	for len(lhs) == 2 && cr == 1 {
+		stmt := stmt.(*ir.AssignListStmt)
+		r := rhs[0]
+
+		switch r.Op() {
+		case ir.OINDEXMAP:
+			stmt.SetOp(ir.OAS2MAPR)
+		case ir.ORECV:
+			stmt.SetOp(ir.OAS2RECV)
+		case ir.ODOTTYPE:
+			r := r.(*ir.TypeAssertExpr)
+			stmt.SetOp(ir.OAS2DOTTYPE)
+			r.SetOp(ir.ODOTTYPE2)
+		default:
+			break assignOK
+		}
+		checkLHS(0, r.Type())
+		checkLHS(1, types.UntypedBool)
+		return
+	}
+
+	if len(lhs) != cr {
+		for i := range lhs {
+			checkLHS(i, nil)
+		}
+		return
+	}
+
+	// x,y,z = f()
+	if cr > len(rhs) {
+		stmt := stmt.(*ir.AssignListStmt)
+		stmt.SetOp(ir.OAS2FUNC)
+		r := rhs[0].(*ir.CallExpr)
+		r.Use = ir.CallUseList
+		rtyp := r.Type()
+
+		for i := range lhs {
+			checkLHS(i, rtyp.Field(i).Type)
+		}
+		return
+	}
+
+	for i, r := range rhs {
+		checkLHS(i, r.Type())
+		if lhs[i].Type() != nil {
+			rhs[i] = assignconvfn(r, lhs[i].Type())
+		}
+	}
+}
+
+// Corresponds to typecheck.typecheckargs.
+func transformArgs(n ir.InitNode) {
+	var list []ir.Node
+	switch n := n.(type) {
+	default:
+		base.Fatalf("typecheckargs %+v", n.Op())
+	case *ir.CallExpr:
+		list = n.Args
+		if n.IsDDD {
+			return
+		}
+	case *ir.ReturnStmt:
+		list = n.Results
+	}
+	if len(list) != 1 {
+		return
+	}
+
+	t := list[0].Type()
+	if t == nil || !t.IsFuncArgStruct() {
+		return
+	}
+
+	// Rewrite f(g()) into t1, t2, ... = g(); f(t1, t2, ...).
+
+	// Save n as n.Orig for fmt.go.
+	if ir.Orig(n) == n {
+		n.(ir.OrigNode).SetOrig(ir.SepCopy(n))
+	}
+
+	as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, nil)
+	as.Rhs.Append(list...)
+
+	// If we're outside of function context, then this call will
+	// be executed during the generated init function. However,
+	// init.go hasn't yet created it. Instead, associate the
+	// temporary variables with  InitTodoFunc for now, and init.go
+	// will reassociate them later when it's appropriate.
+	static := ir.CurFunc == nil
+	if static {
+		ir.CurFunc = typecheck.InitTodoFunc
+	}
+	list = nil
+	for _, f := range t.FieldSlice() {
+		t := typecheck.Temp(f.Type)
+		as.PtrInit().Append(ir.NewDecl(base.Pos, ir.ODCL, t))
+		as.Lhs.Append(t)
+		list = append(list, t)
+	}
+	if static {
+		ir.CurFunc = nil
+	}
+
+	switch n := n.(type) {
+	case *ir.CallExpr:
+		n.Args = list
+	case *ir.ReturnStmt:
+		n.Results = list
+	}
+
+	transformAssign(as, as.Lhs, as.Rhs)
+	as.SetTypecheck(1)
+	n.PtrInit().Append(as)
+}
+
+// assignconvfn converts node n for assignment to type t. Corresponds to
+// typecheck.assignconvfn.
+func assignconvfn(n ir.Node, t *types.Type) ir.Node {
+	if t.Kind() == types.TBLANK {
+		return n
+	}
+
+	if types.Identical(n.Type(), t) {
+		return n
+	}
+
+	op, _ := typecheck.Assignop(n.Type(), t)
+
+	r := ir.NewConvExpr(base.Pos, op, t, n)
+	r.SetTypecheck(1)
+	r.SetImplicit(true)
+	return r
+}
+
+// Corresponds to typecheck.typecheckaste.
+func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl ir.Nodes) {
+	var t *types.Type
+	var i int
+
+	lno := base.Pos
+	defer func() { base.Pos = lno }()
+
+	var n ir.Node
+	if len(nl) == 1 {
+		n = nl[0]
+	}
+
+	i = 0
+	for _, tl := range tstruct.Fields().Slice() {
+		t = tl.Type
+		if tl.IsDDD() {
+			if isddd {
+				n = nl[i]
+				ir.SetPos(n)
+				if n.Type() != nil {
+					nl[i] = assignconvfn(n, t)
+				}
+				return
+			}
+
+			// TODO(mdempsky): Make into ... call with implicit slice.
+			for ; i < len(nl); i++ {
+				n = nl[i]
+				ir.SetPos(n)
+				if n.Type() != nil {
+					nl[i] = assignconvfn(n, t.Elem())
+				}
+			}
+			return
+		}
+
+		n = nl[i]
+		ir.SetPos(n)
+		if n.Type() != nil {
+			nl[i] = assignconvfn(n, t)
+		}
+		i++
+	}
+}
+
+// transformSend transforms a send statement, converting the value to appropriate
+// type for the channel, as needed. Corresponds of typecheck.tcSend.
+func transformSend(n *ir.SendStmt) {
+	n.Value = assignconvfn(n.Value, n.Chan.Type().Elem())
+}
+
+// transformReturn transforms a return node, by doing the needed assignments and
+// any necessary conversions. Corresponds to typecheck.tcReturn()
+func transformReturn(rs *ir.ReturnStmt) {
+	transformArgs(rs)
+	nl := rs.Results
+	if ir.HasNamedResults(ir.CurFunc) && len(nl) == 0 {
+		return
+	}
+
+	typecheckaste(ir.ORETURN, nil, false, ir.CurFunc.Type().Results(), nl)
+}
+
+// transformSelect transforms a select node, creating an assignment list as needed
+// for each case. Corresponds to typecheck.tcSelect().
+func transformSelect(sel *ir.SelectStmt) {
+	for _, ncase := range sel.Cases {
+		if ncase.Comm != nil {
+			n := ncase.Comm
+			oselrecv2 := func(dst, recv ir.Node, def bool) {
+				n := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
+				n.Def = def
+				n.SetTypecheck(1)
+				ncase.Comm = n
+			}
+			switch n.Op() {
+			case ir.OAS:
+				// convert x = <-c into x, _ = <-c
+				// remove implicit conversions; the eventual assignment
+				// will reintroduce them.
+				n := n.(*ir.AssignStmt)
+				if r := n.Y; r.Op() == ir.OCONVNOP || r.Op() == ir.OCONVIFACE {
+					r := r.(*ir.ConvExpr)
+					if r.Implicit() {
+						n.Y = r.X
+					}
+				}
+				oselrecv2(n.X, n.Y, n.Def)
+
+			case ir.OAS2RECV:
+				n := n.(*ir.AssignListStmt)
+				n.SetOp(ir.OSELRECV2)
+
+			case ir.ORECV:
+				// convert <-c into _, _ = <-c
+				n := n.(*ir.UnaryExpr)
+				oselrecv2(ir.BlankNode, n, false)
+
+			case ir.OSEND:
+				break
+			}
+		}
+	}
+}
+
+// transformAsOp transforms an AssignOp statement. Corresponds to OASOP case in
+// typecheck1.
+func transformAsOp(n *ir.AssignOpStmt) {
+	transformCheckAssign(n, n.X)
+}