[dev.regabi] cmd/compile: setup for new Node implementations

Start a list of which ops are valid for the default
node struct implementation (currently all of them).

Add a Node implementation helper for a minimal node.

Passes buildall w/ toolstash -cmp.

Change-Id: I7ae45f2cf2be85013cb71ab00524be53f243e13d
Reviewed-on: https://go-review.googlesource.com/c/go/+/274088
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>

4 files changed, 424 insertions, 40 deletions

diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index ede3778184..9da464e1b6 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -1694,8 +1694,7 @@ func typecheck1(n ir.Node, top int) (res ir.Node) {
 			return n
 		}
 		op, why := convertop(n.Left().Op() == ir.OLITERAL, t, n.Type())
-		n.SetOp(op)
-		if n.Op() == ir.OXXX {
+		if op == ir.OXXX {
 			if !n.Diag() && !n.Type().Broke() && !n.Left().Diag() {
 				base.Errorf("cannot convert %L to type %v%s", n.Left(), n.Type(), why)
 				n.SetDiag(true)
@@ -1705,6 +1704,7 @@ func typecheck1(n ir.Node, top int) (res ir.Node) {
 			return n
 		}
 
+		n.SetOp(op)
 		switch n.Op() {
 		case ir.OCONVNOP:
 			if t.Etype == n.Type().Etype {
diff --git a/src/cmd/compile/internal/ir/bitset.go b/src/cmd/compile/internal/ir/bitset.go
index 29f136296f..0c7bd542f6 100644
--- a/src/cmd/compile/internal/ir/bitset.go
+++ b/src/cmd/compile/internal/ir/bitset.go
@@ -14,6 +14,18 @@ func (f *bitset8) set(mask uint8, b bool) {
 	}
 }
 
+func (f bitset8) get2(shift uint8) uint8 {
+	return uint8(f>>shift) & 3
+}
+
+// set2 sets two bits in f using the bottom two bits of b.
+func (f *bitset8) set2(shift uint8, b uint8) {
+	// Clear old bits.
+	*(*uint8)(f) &^= 3 << shift
+	// Set new bits.
+	*(*uint8)(f) |= uint8(b&3) << shift
+}
+
 type bitset16 uint16
 
 func (f *bitset16) set(mask uint16, b bool) {
diff --git a/src/cmd/compile/internal/ir/mini.go b/src/cmd/compile/internal/ir/mini.go
new file mode 100644
index 0000000000..48dccf6a5f
--- /dev/null
+++ b/src/cmd/compile/internal/ir/mini.go
@@ -0,0 +1,188 @@
+// Copyright 2020 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 ir
+
+import (
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+	"fmt"
+	"go/constant"
+)
+
+// A miniNode is a minimal node implementation,
+// meant to be embedded as the first field in a larger node implementation,
+// at a cost of 8 bytes.
+//
+// A miniNode is NOT a valid Node by itself: the embedding struct
+// must at the least provide:
+//
+//	func (n *MyNode) String() string { return fmt.Sprint(n) }
+//	func (n *MyNode) RawCopy() Node { c := *n; return &c }
+//	func (n *MyNode) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
+//
+// The embedding struct should also fill in n.op in its constructor,
+// for more useful panic messages when invalid methods are called,
+// instead of implementing Op itself.
+//
+type miniNode struct {
+	pos  src.XPos // uint32
+	op   Op       // uint8
+	bits bitset8
+	esc  uint16
+}
+
+// op can be read, but not written.
+// An embedding implementation can provide a SetOp if desired.
+// (The panicking SetOp is with the other panics below.)
+func (n *miniNode) Op() Op            { return n.op }
+func (n *miniNode) Pos() src.XPos     { return n.pos }
+func (n *miniNode) SetPos(x src.XPos) { n.pos = x }
+func (n *miniNode) Esc() uint16       { return n.esc }
+func (n *miniNode) SetEsc(x uint16)   { n.esc = x }
+
+const (
+	miniWalkdefShift   = 0
+	miniTypecheckShift = 2
+	miniInitorderShift = 4
+	miniDiag           = 1 << 6
+	miniHasCall        = 1 << 7 // for miniStmt
+)
+
+func (n *miniNode) Walkdef() uint8   { return n.bits.get2(miniWalkdefShift) }
+func (n *miniNode) Typecheck() uint8 { return n.bits.get2(miniTypecheckShift) }
+func (n *miniNode) Initorder() uint8 { return n.bits.get2(miniInitorderShift) }
+func (n *miniNode) SetWalkdef(x uint8) {
+	if x > 3 {
+		panic(fmt.Sprintf("cannot SetWalkdef %d", x))
+	}
+	n.bits.set2(miniWalkdefShift, x)
+}
+func (n *miniNode) SetTypecheck(x uint8) {
+	if x > 3 {
+		panic(fmt.Sprintf("cannot SetTypecheck %d", x))
+	}
+	n.bits.set2(miniTypecheckShift, x)
+}
+func (n *miniNode) SetInitorder(x uint8) {
+	if x > 3 {
+		panic(fmt.Sprintf("cannot SetInitorder %d", x))
+	}
+	n.bits.set2(miniInitorderShift, x)
+}
+
+func (n *miniNode) Diag() bool     { return n.bits&miniDiag != 0 }
+func (n *miniNode) SetDiag(x bool) { n.bits.set(miniDiag, x) }
+
+// Empty, immutable graph structure.
+
+func (n *miniNode) Left() Node       { return nil }
+func (n *miniNode) Right() Node      { return nil }
+func (n *miniNode) Init() Nodes      { return Nodes{} }
+func (n *miniNode) PtrInit() *Nodes  { return &immutableEmptyNodes }
+func (n *miniNode) Body() Nodes      { return Nodes{} }
+func (n *miniNode) PtrBody() *Nodes  { return &immutableEmptyNodes }
+func (n *miniNode) List() Nodes      { return Nodes{} }
+func (n *miniNode) PtrList() *Nodes  { return &immutableEmptyNodes }
+func (n *miniNode) Rlist() Nodes     { return Nodes{} }
+func (n *miniNode) PtrRlist() *Nodes { return &immutableEmptyNodes }
+func (n *miniNode) SetLeft(x Node) {
+	if x != nil {
+		panic(n.no("SetLeft"))
+	}
+}
+func (n *miniNode) SetRight(x Node) {
+	if x != nil {
+		panic(n.no("SetRight"))
+	}
+}
+func (n *miniNode) SetInit(x Nodes) {
+	if x != (Nodes{}) {
+		panic(n.no("SetInit"))
+	}
+}
+func (n *miniNode) SetBody(x Nodes) {
+	if x != (Nodes{}) {
+		panic(n.no("SetBody"))
+	}
+}
+func (n *miniNode) SetList(x Nodes) {
+	if x != (Nodes{}) {
+		panic(n.no("SetList"))
+	}
+}
+func (n *miniNode) SetRlist(x Nodes) {
+	if x != (Nodes{}) {
+		panic(n.no("SetRlist"))
+	}
+}
+
+// Additional functionality unavailable.
+
+func (n *miniNode) no(name string) string { return "cannot " + name + " on " + n.op.String() }
+
+func (n *miniNode) SetOp(Op)            { panic(n.no("SetOp")) }
+func (n *miniNode) SubOp() Op           { panic(n.no("SubOp")) }
+func (n *miniNode) SetSubOp(Op)         { panic(n.no("SetSubOp")) }
+func (n *miniNode) Type() *types.Type   { return nil }
+func (n *miniNode) SetType(*types.Type) { panic(n.no("SetType")) }
+func (n *miniNode) Func() *Func         { panic(n.no("Func")) }
+func (n *miniNode) SetFunc(*Func)       { panic(n.no("SetFunc")) }
+func (n *miniNode) Name() *Name         { return nil }
+func (n *miniNode) SetName(*Name)       { panic(n.no("SetName")) }
+func (n *miniNode) Sym() *types.Sym     { return nil }
+func (n *miniNode) SetSym(*types.Sym)   { panic(n.no("SetSym")) }
+func (n *miniNode) Offset() int64       { return types.BADWIDTH }
+func (n *miniNode) SetOffset(x int64)   { panic(n.no("SetOffset")) }
+func (n *miniNode) Class() Class        { return Pxxx }
+func (n *miniNode) SetClass(Class)      { panic(n.no("SetClass")) }
+func (n *miniNode) Likely() bool        { panic(n.no("Likely")) }
+func (n *miniNode) SetLikely(bool)      { panic(n.no("SetLikely")) }
+func (n *miniNode) SliceBounds() (low, high, max Node) {
+	panic(n.no("SliceBounds"))
+}
+func (n *miniNode) SetSliceBounds(low, high, max Node) {
+	panic(n.no("SetSliceBounds"))
+}
+func (n *miniNode) Iota() int64               { panic(n.no("Iota")) }
+func (n *miniNode) SetIota(int64)             { panic(n.no("SetIota")) }
+func (n *miniNode) Colas() bool               { return false }
+func (n *miniNode) SetColas(bool)             { panic(n.no("SetColas")) }
+func (n *miniNode) NoInline() bool            { panic(n.no("NoInline")) }
+func (n *miniNode) SetNoInline(bool)          { panic(n.no("SetNoInline")) }
+func (n *miniNode) Transient() bool           { panic(n.no("Transient")) }
+func (n *miniNode) SetTransient(bool)         { panic(n.no("SetTransient")) }
+func (n *miniNode) Implicit() bool            { return false }
+func (n *miniNode) SetImplicit(bool)          { panic(n.no("SetImplicit")) }
+func (n *miniNode) IsDDD() bool               { return false }
+func (n *miniNode) SetIsDDD(bool)             { panic(n.no("SetIsDDD")) }
+func (n *miniNode) Embedded() bool            { return false }
+func (n *miniNode) SetEmbedded(bool)          { panic(n.no("SetEmbedded")) }
+func (n *miniNode) IndexMapLValue() bool      { panic(n.no("IndexMapLValue")) }
+func (n *miniNode) SetIndexMapLValue(bool)    { panic(n.no("SetIndexMapLValue")) }
+func (n *miniNode) ResetAux()                 { panic(n.no("ResetAux")) }
+func (n *miniNode) HasBreak() bool            { panic(n.no("HasBreak")) }
+func (n *miniNode) SetHasBreak(bool)          { panic(n.no("SetHasBreak")) }
+func (n *miniNode) HasVal() bool              { return false }
+func (n *miniNode) Val() constant.Value       { panic(n.no("Val")) }
+func (n *miniNode) SetVal(v constant.Value)   { panic(n.no("SetVal")) }
+func (n *miniNode) Int64Val() int64           { panic(n.no("Int64Val")) }
+func (n *miniNode) Uint64Val() uint64         { panic(n.no("Uint64Val")) }
+func (n *miniNode) CanInt64() bool            { panic(n.no("CanInt64")) }
+func (n *miniNode) BoolVal() bool             { panic(n.no("BoolVal")) }
+func (n *miniNode) StringVal() string         { panic(n.no("StringVal")) }
+func (n *miniNode) HasCall() bool             { panic(n.no("HasCall")) }
+func (n *miniNode) SetHasCall(bool)           { panic(n.no("SetHasCall")) }
+func (n *miniNode) NonNil() bool              { return false }
+func (n *miniNode) MarkNonNil()               { panic(n.no("MarkNonNil")) }
+func (n *miniNode) Bounded() bool             { return false }
+func (n *miniNode) SetBounded(bool)           { panic(n.no("SetBounded")) }
+func (n *miniNode) Opt() interface{}          { return nil }
+func (n *miniNode) SetOpt(interface{})        { panic(n.no("SetOpt")) }
+func (n *miniNode) MarkReadonly()             { panic(n.no("MarkReadonly")) }
+func (n *miniNode) TChanDir() types.ChanDir   { panic(n.no("TChanDir")) }
+func (n *miniNode) SetTChanDir(types.ChanDir) { panic(n.no("SetTChanDir")) }
+
+// TODO: Delete when CanBeAnSSASym is removed from Node itself.
+func (*miniNode) CanBeAnSSASym() {}
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index acfddd2dc7..7a61355858 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -199,7 +199,6 @@ func (n *node) SetOffset(x int64)     { n.offset = x }
 func (n *node) Esc() uint16           { return n.esc }
 func (n *node) SetEsc(x uint16)       { n.esc = x }
 func (n *node) Op() Op                { return n.op }
-func (n *node) SetOp(x Op)            { n.op = x }
 func (n *node) Init() Nodes           { return n.init }
 func (n *node) SetInit(x Nodes)       { n.init = x }
 func (n *node) PtrInit() *Nodes       { return &n.init }
@@ -213,6 +212,13 @@ func (n *node) Rlist() Nodes          { return n.rlist }
 func (n *node) SetRlist(x Nodes)      { n.rlist = x }
 func (n *node) PtrRlist() *Nodes      { return &n.rlist }
 
+func (n *node) SetOp(op Op) {
+	if !okForNod[op] {
+		panic("cannot node.SetOp " + op.String())
+	}
+	n.op = op
+}
+
 func (n *node) ResetAux() {
 	n.aux = 0
 }
@@ -1109,6 +1115,10 @@ const (
 // a slice to save space.
 type Nodes struct{ slice *[]Node }
 
+// immutableEmptyNodes is an immutable, empty Nodes list.
+// The methods that would modify it panic instead.
+var immutableEmptyNodes = Nodes{}
+
 // asNodes returns a slice of *Node as a Nodes value.
 func AsNodes(s []Node) Nodes {
 	return Nodes{&s}
@@ -1150,9 +1160,22 @@ func (n Nodes) Second() Node {
 	return (*n.slice)[1]
 }
 
+func (n *Nodes) mutate() {
+	if n == &immutableEmptyNodes {
+		panic("immutable Nodes.Set")
+	}
+}
+
 // Set sets n to a slice.
 // This takes ownership of the slice.
 func (n *Nodes) Set(s []Node) {
+	if n == &immutableEmptyNodes {
+		if len(s) == 0 {
+			// Allow immutableEmptyNodes.Set(nil) (a no-op).
+			return
+		}
+		n.mutate()
+	}
 	if len(s) == 0 {
 		n.slice = nil
 	} else {
@@ -1166,21 +1189,25 @@ func (n *Nodes) Set(s []Node) {
 
 // Set1 sets n to a slice containing a single node.
 func (n *Nodes) Set1(n1 Node) {
+	n.mutate()
 	n.slice = &[]Node{n1}
 }
 
 // Set2 sets n to a slice containing two nodes.
 func (n *Nodes) Set2(n1, n2 Node) {
+	n.mutate()
 	n.slice = &[]Node{n1, n2}
 }
 
 // Set3 sets n to a slice containing three nodes.
 func (n *Nodes) Set3(n1, n2, n3 Node) {
+	n.mutate()
 	n.slice = &[]Node{n1, n2, n3}
 }
 
 // MoveNodes sets n to the contents of n2, then clears n2.
 func (n *Nodes) MoveNodes(n2 *Nodes) {
+	n.mutate()
 	n.slice = n2.slice
 	n2.slice = nil
 }
@@ -1214,6 +1241,7 @@ func (n *Nodes) Append(a ...Node) {
 	if len(a) == 0 {
 		return
 	}
+	n.mutate()
 	if n.slice == nil {
 		s := make([]Node, len(a))
 		copy(s, a)
@@ -1229,6 +1257,7 @@ func (n *Nodes) Prepend(a ...Node) {
 	if len(a) == 0 {
 		return
 	}
+	n.mutate()
 	if n.slice == nil {
 		n.slice = &a
 	} else {
@@ -1238,6 +1267,7 @@ func (n *Nodes) Prepend(a ...Node) {
 
 // AppendNodes appends the contents of *n2 to n, then clears n2.
 func (n *Nodes) AppendNodes(n2 *Nodes) {
+	n.mutate()
 	switch {
 	case n2.slice == nil:
 	case n.slice == nil:
@@ -1341,43 +1371,7 @@ func (s NodeSet) Sorted(less func(Node, Node) bool) []Node {
 	return res
 }
 
-func Nod(op Op, nleft, nright Node) Node {
-	return NodAt(base.Pos, op, nleft, nright)
-}
-
-func NodAt(pos src.XPos, op Op, nleft, nright Node) Node {
-	var n Node
-	switch op {
-	case ODCLFUNC:
-		var x struct {
-			n node
-			f Func
-		}
-		n = &x.n
-		n.SetFunc(&x.f)
-		n.Func().Decl = n
-	case ONAME:
-		base.Fatalf("use newname instead")
-	case OLABEL, OPACK:
-		var x struct {
-			n node
-			m Name
-		}
-		n = &x.n
-		n.SetName(&x.m)
-	default:
-		n = new(node)
-	}
-	n.SetOp(op)
-	n.SetLeft(nleft)
-	n.SetRight(nright)
-	n.SetPos(pos)
-	n.SetOffset(types.BADWIDTH)
-	n.SetOrig(n)
-	return n
-}
-
-// newnamel returns a new ONAME Node associated with symbol s at position pos.
+// NewNameAt returns a new ONAME Node associated with symbol s at position pos.
 // The caller is responsible for setting n.Name.Curfn.
 func NewNameAt(pos src.XPos, s *types.Sym) Node {
 	if s == nil {
@@ -1664,3 +1658,193 @@ func IsBlank(n Node) bool {
 func IsMethod(n Node) bool {
 	return n.Type().Recv() != nil
 }
+
+func Nod(op Op, nleft, nright Node) Node {
+	return NodAt(base.Pos, op, nleft, nright)
+}
+
+func NodAt(pos src.XPos, op Op, nleft, nright Node) Node {
+	var n Node
+	switch op {
+	case ODCLFUNC:
+		var x struct {
+			n node
+			f Func
+		}
+		n = &x.n
+		n.SetFunc(&x.f)
+		n.Func().Decl = n
+	case OLABEL, OPACK:
+		var x struct {
+			n node
+			m Name
+		}
+		n = &x.n
+		n.SetName(&x.m)
+	default:
+		n = new(node)
+	}
+	n.SetOp(op)
+	n.SetLeft(nleft)
+	n.SetRight(nright)
+	n.SetPos(pos)
+	n.SetOffset(types.BADWIDTH)
+	n.SetOrig(n)
+	return n
+}
+
+var okForNod = [OEND]bool{
+	OADD:           true,
+	OADDR:          true,
+	OADDSTR:        true,
+	OALIGNOF:       true,
+	OAND:           true,
+	OANDAND:        true,
+	OANDNOT:        true,
+	OAPPEND:        true,
+	OARRAYLIT:      true,
+	OAS:            true,
+	OAS2:           true,
+	OAS2DOTTYPE:    true,
+	OAS2FUNC:       true,
+	OAS2MAPR:       true,
+	OAS2RECV:       true,
+	OASOP:          true,
+	OBITNOT:        true,
+	OBLOCK:         true,
+	OBREAK:         true,
+	OBYTES2STR:     true,
+	OBYTES2STRTMP:  true,
+	OCALL:          true,
+	OCALLFUNC:      true,
+	OCALLINTER:     true,
+	OCALLMETH:      true,
+	OCALLPART:      true,
+	OCAP:           true,
+	OCASE:          true,
+	OCFUNC:         true,
+	OCHECKNIL:      true,
+	OCLOSE:         true,
+	OCLOSURE:       true,
+	OCLOSUREVAR:    true,
+	OCOMPLEX:       true,
+	OCOMPLIT:       true,
+	OCONTINUE:      true,
+	OCONV:          true,
+	OCONVIFACE:     true,
+	OCONVNOP:       true,
+	OCOPY:          true,
+	ODCL:           true,
+	ODCLCONST:      true,
+	ODCLFIELD:      true,
+	ODCLFUNC:       true,
+	ODCLTYPE:       true,
+	ODDD:           true,
+	ODEFER:         true,
+	ODELETE:        true,
+	ODEREF:         true,
+	ODIV:           true,
+	ODOT:           true,
+	ODOTINTER:      true,
+	ODOTMETH:       true,
+	ODOTPTR:        true,
+	ODOTTYPE:       true,
+	ODOTTYPE2:      true,
+	OEFACE:         true,
+	OEMPTY:         true,
+	OEQ:            true,
+	OFALL:          true,
+	OFOR:           true,
+	OFORUNTIL:      true,
+	OGE:            true,
+	OGETG:          true,
+	OGO:            true,
+	OGOTO:          true,
+	OGT:            true,
+	OIDATA:         true,
+	OIF:            true,
+	OIMAG:          true,
+	OINDEX:         true,
+	OINDEXMAP:      true,
+	OINLCALL:       true,
+	OINLMARK:       true,
+	OIOTA:          true,
+	OITAB:          true,
+	OKEY:           true,
+	OLABEL:         true,
+	OLE:            true,
+	OLEN:           true,
+	OLITERAL:       true,
+	OLSH:           true,
+	OLT:            true,
+	OMAKE:          true,
+	OMAKECHAN:      true,
+	OMAKEMAP:       true,
+	OMAKESLICE:     true,
+	OMAKESLICECOPY: true,
+	OMAPLIT:        true,
+	OMETHEXPR:      true,
+	OMOD:           true,
+	OMUL:           true,
+	ONAME:          true,
+	ONE:            true,
+	ONEG:           true,
+	ONEW:           true,
+	ONEWOBJ:        true,
+	ONIL:           true,
+	ONONAME:        true,
+	ONOT:           true,
+	OOFFSETOF:      true,
+	OOR:            true,
+	OOROR:          true,
+	OPACK:          true,
+	OPANIC:         true,
+	OPAREN:         true,
+	OPLUS:          true,
+	OPRINT:         true,
+	OPRINTN:        true,
+	OPTRLIT:        true,
+	ORANGE:         true,
+	OREAL:          true,
+	ORECOVER:       true,
+	ORECV:          true,
+	ORESULT:        true,
+	ORETJMP:        true,
+	ORETURN:        true,
+	ORSH:           true,
+	ORUNES2STR:     true,
+	ORUNESTR:       true,
+	OSELECT:        true,
+	OSELRECV:       true,
+	OSELRECV2:      true,
+	OSEND:          true,
+	OSIZEOF:        true,
+	OSLICE:         true,
+	OSLICE3:        true,
+	OSLICE3ARR:     true,
+	OSLICEARR:      true,
+	OSLICEHEADER:   true,
+	OSLICELIT:      true,
+	OSLICESTR:      true,
+	OSPTR:          true,
+	OSTR2BYTES:     true,
+	OSTR2BYTESTMP:  true,
+	OSTR2RUNES:     true,
+	OSTRUCTKEY:     true,
+	OSTRUCTLIT:     true,
+	OSUB:           true,
+	OSWITCH:        true,
+	OTARRAY:        true,
+	OTCHAN:         true,
+	OTFUNC:         true,
+	OTINTER:        true,
+	OTMAP:          true,
+	OTSTRUCT:       true,
+	OTYPE:          true,
+	OTYPESW:        true,
+	OVARDEF:        true,
+	OVARKILL:       true,
+	OVARLIVE:       true,
+	OXDOT:          true,
+	OXOR:           true,
+}