cmd/compile: split TSLICE into separate Type kind

Instead of using TARRAY for both arrays and slices, create a new
TSLICE kind to handle slices.

Also, get rid of the "DDDArray" distinction. While kinda ugly, it
seems likely we'll need to defer evaluating the constant bounds
expressions for golang.org/issue/13890.

Passes toolstash/buildall.

Change-Id: I8e45d4900e7df3a04cce59428ec8b38035d3cc3a
Reviewed-on: https://go-review.googlesource.com/22329Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/alg.go

@@ -127,11 +127,10 @@ func algtype1(t *Type) (AlgKind, *Type) {
 		}
 		return AINTER, nil
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		return ANOEQ, t
-		}
 
+	case TARRAY:
 		a, bad := algtype1(t.Elem())
 		switch a {
 		case AMEM:
@@ -219,10 +218,6 @@ func genhash(sym *Sym, t *Type) {
 		Fatalf("genhash %v", t)
 
 	case TARRAY:
-		if t.IsSlice() {
-			Fatalf("genhash %v", t)
-		}
-
 		// An array of pure memory would be handled by the
 		// standard algorithm, so the element type must not be
 		// pure memory.
@@ -399,10 +394,6 @@ func geneq(sym *Sym, t *Type) {
 		Fatalf("geneq %v", t)
 
 	case TARRAY:
-		if t.IsSlice() {
-			Fatalf("geneq %v", t)
-		}
-
 		// An array of pure memory would be handled by the
 		// standard memequal, so the element type must not be
 		// pure memory. Even if we unrolled the range loop,

src/cmd/compile/internal/gc/align.go

@@ -238,7 +238,14 @@ func dowidth(t *Type) {
 		if t.Elem() == nil {
 			break
 		}
-		if t.IsArray() {
+		if t.isDDDArray() {
+			if !t.Broke {
+				Yyerror("use of [...] array outside of array literal")
+				t.Broke = true
+			}
+			break
+		}
+
 		dowidth(t.Elem())
 		if t.Elem().Width != 0 {
 			cap := (uint64(Thearch.MAXWIDTH) - 1) / uint64(t.Elem().Width)
@@ -246,21 +253,16 @@ func dowidth(t *Type) {
 				Yyerror("type %v larger than address space", Tconv(t, FmtLong))
 			}
 		}
-
 		w = t.NumElem() * t.Elem().Width
 		t.Align = t.Elem().Align
-		} else if t.IsSlice() {
+
+	case TSLICE:
+		if t.Elem() == nil {
+			break
+		}
 		w = int64(sizeof_Array)
 		checkwidth(t.Elem())
 		t.Align = uint8(Widthptr)
-		} else if t.isDDDArray() {
-			if !t.Broke {
-				Yyerror("use of [...] array outside of array literal")
-				t.Broke = true
-			}
-		} else {
-			Fatalf("dowidth %v", t) // probably [...]T
-		}
 
 	case TSTRUCT:
 		if t.IsFuncArgStruct() {

src/cmd/compile/internal/gc/bexport.go

@@ -629,12 +629,12 @@ func (p *exporter) typ(t *Type) {
 		if t.isDDDArray() {
 			Fatalf("array bounds should be known at export time: %v", t)
 		}
-		if t.IsArray() {
 		p.tag(arrayTag)
 		p.int64(t.NumElem())
-		} else {
+		p.typ(t.Elem())
+
+	case TSLICE:
 		p.tag(sliceTag)
-		}
 		p.typ(t.Elem())
 
 	case TDDDFIELD:

src/cmd/compile/internal/gc/bimport.go

@@ -369,18 +369,16 @@ func (p *importer) typ() *Type {
 
 		dclcontext = savedContext
 
-	case arrayTag, sliceTag:
+	case arrayTag:
 		t = p.newtyp(TARRAY)
-		var bound int64
-		if i == arrayTag {
-			bound = p.int64()
-		}
+		bound := p.int64()
 		elem := p.typ()
-		if i == arrayTag {
 		t.Extra = &ArrayType{Elem: elem, Bound: bound}
-		} else {
+
+	case sliceTag:
+		t = p.newtyp(TSLICE)
+		elem := p.typ()
 		t.Extra = SliceType{Elem: elem}
-		}
 
 	case dddTag:
 		t = p.newtyp(TDDDFIELD)

src/cmd/compile/internal/gc/const.go

@@ -284,9 +284,7 @@ func convlit1(n *Node, t *Type, explicit bool, reuse canReuseNode) *Node {
 			return n
 
 		case TARRAY:
-			if !t.IsSlice() {
 			goto bad
-			}
 
 		case TPTR32,
 			TPTR64,
@@ -294,6 +292,7 @@ func convlit1(n *Node, t *Type, explicit bool, reuse canReuseNode) *Node {
 			TMAP,
 			TCHAN,
 			TFUNC,
+			TSLICE,
 			TUNSAFEPTR:
 			break
 

src/cmd/compile/internal/gc/export.go

@@ -203,7 +203,7 @@ func reexportdep(n *Node) {
 		t := n.Type
 
 		switch t.Etype {
-		case TARRAY, TCHAN, TPTR32, TPTR64:
+		case TARRAY, TCHAN, TPTR32, TPTR64, TSLICE:
 			if t.Sym == nil {
 				t = t.Elem()
 			}
@@ -303,7 +303,7 @@ func dumpexporttype(t *Type) {
 	case TMAP:
 		dumpexporttype(t.Val())
 		dumpexporttype(t.Key())
-	case TARRAY, TCHAN, TPTR32, TPTR64:
+	case TARRAY, TCHAN, TPTR32, TPTR64, TSLICE:
 		dumpexporttype(t.Elem())
 	}
 

src/cmd/compile/internal/gc/fmt.go

@@ -416,6 +416,7 @@ var etnames = []string{
 	TPTR64:      "PTR64",
 	TFUNC:       "FUNC",
 	TARRAY:      "ARRAY",
+	TSLICE:      "SLICE",
 	TSTRUCT:     "STRUCT",
 	TCHAN:       "CHAN",
 	TMAP:        "MAP",
@@ -587,12 +588,12 @@ func typefmt(t *Type, flag FmtFlag) string {
 		return "*" + t.Elem().String()
 
 	case TARRAY:
-		if t.IsArray() {
-			return fmt.Sprintf("[%d]%v", t.NumElem(), t.Elem())
-		}
 		if t.isDDDArray() {
 			return "[...]" + t.Elem().String()
 		}
+		return fmt.Sprintf("[%d]%v", t.NumElem(), t.Elem())
+
+	case TSLICE:
 		return "[]" + t.Elem().String()
 
 	case TCHAN:

src/cmd/compile/internal/gc/gen.go

@@ -1031,7 +1031,7 @@ func componentgen_wb(nr, nl *Node, wb bool) bool {
 		// Emit vardef if needed.
 		if nl.Op == ONAME {
 			switch nl.Type.Etype {
-			case TARRAY, TSTRING, TINTER, TSTRUCT:
+			case TARRAY, TSLICE, TSTRING, TINTER, TSTRUCT:
 				Gvardef(nl)
 			}
 		}
@@ -1204,13 +1204,12 @@ func visitComponents(t *Type, startOffset int64, f func(elem *Type, elemOffset i
 		return f(Ptrto(Types[TUINT8]), startOffset) &&
 			f(Types[Simtype[TUINT]], startOffset+int64(Widthptr))
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		return f(Ptrto(t.Elem()), startOffset+int64(Array_array)) &&
 			f(Types[Simtype[TUINT]], startOffset+int64(Array_nel)) &&
 			f(Types[Simtype[TUINT]], startOffset+int64(Array_cap))
-		}
 
+	case TARRAY:
 		// Short-circuit [1e6]struct{}.
 		if t.Elem().Width == 0 {
 			return true

src/cmd/compile/internal/gc/gsubr.go

@@ -277,7 +277,7 @@ func gused(n *Node) {
 func Isfat(t *Type) bool {
 	if t != nil {
 		switch t.Etype {
-		case TSTRUCT, TARRAY, TSTRING,
+		case TSTRUCT, TARRAY, TSLICE, TSTRING,
 			TINTER: // maybe remove later
 			return true
 		}

src/cmd/compile/internal/gc/order.go

@@ -731,7 +731,7 @@ func orderstmt(n *Node, order *Order) {
 		default:
 			Fatalf("orderstmt range %v", n.Type)
 
-		case TARRAY:
+		case TARRAY, TSLICE:
 			if n.List.Len() < 2 || isblank(n.List.Second()) {
 				// for i := range x will only use x once, to compute len(x).
 				// No need to copy it.

src/cmd/compile/internal/gc/plive.go

@@ -918,19 +918,18 @@ func onebitwalktype1(t *Type, xoffset *int64, bv Bvec) {
 		bvset(bv, int32(*xoffset/int64(Widthptr)+1)) // pointer in second slot
 		*xoffset += t.Width
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		// struct { byte *array; uintgo len; uintgo cap; }
 		if *xoffset&int64(Widthptr-1) != 0 {
 			Fatalf("onebitwalktype1: invalid TARRAY alignment, %v", t)
 		}
 		bvset(bv, int32(*xoffset/int64(Widthptr))) // pointer in first slot (BitsPointer)
 		*xoffset += t.Width
-		} else {
+
+	case TARRAY:
 		for i := int64(0); i < t.NumElem(); i++ {
 			onebitwalktype1(t.Elem(), xoffset, bv)
 		}
-		}
 
 	case TSTRUCT:
 		var o int64

src/cmd/compile/internal/gc/range.go

@@ -49,7 +49,7 @@ func typecheckrange(n *Node) {
 		Yyerror("cannot range over %v", Nconv(n.Right, FmtLong))
 		goto out
 
-	case TARRAY:
+	case TARRAY, TSLICE:
 		t1 = Types[TINT]
 		t2 = t.Elem()
 
@@ -164,7 +164,7 @@ func walkrange(n *Node) {
 	default:
 		Fatalf("walkrange")
 
-	case TARRAY:
+	case TARRAY, TSLICE:
 		if memclrrange(n, v1, v2, a) {
 			lineno = lno
 			return

src/cmd/compile/internal/gc/reflect.go

@@ -623,7 +623,7 @@ func typePkg(t *Type) *Pkg {
 	tsym := t.Sym
 	if tsym == nil {
 		switch t.Etype {
-		case TARRAY, TPTR32, TPTR64, TCHAN:
+		case TARRAY, TSLICE, TPTR32, TPTR64, TCHAN:
 			if t.Elem() != nil {
 				tsym = t.Elem().Sym
 			}
@@ -689,6 +689,7 @@ var kinds = []int{
 	TCHAN:       obj.KindChan,
 	TMAP:        obj.KindMap,
 	TARRAY:      obj.KindArray,
+	TSLICE:      obj.KindArray,
 	TFUNC:       obj.KindFunc,
 	TCOMPLEX64:  obj.KindComplex64,
 	TCOMPLEX128: obj.KindComplex128,
@@ -701,11 +702,10 @@ func haspointers(t *Type) bool {
 		TUINT64, TUINTPTR, TFLOAT32, TFLOAT64, TCOMPLEX64, TCOMPLEX128, TBOOL:
 		return false
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		return true
-		}
 
+	case TARRAY:
 		at := t.Extra.(*ArrayType)
 		if at.Haspointers != 0 {
 			return at.Haspointers-1 != 0
@@ -764,11 +764,11 @@ func typeptrdata(t *Type) int64 {
 		// struct { Type *type; void *data; }
 		return 2 * int64(Widthptr)
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		// struct { byte *array; uintgo len; uintgo cap; }
 		return int64(Widthptr)
-		}
+
+	case TARRAY:
 		// haspointers already eliminated t.NumElem() == 0.
 		return (t.NumElem()-1)*t.Elem().Width + typeptrdata(t.Elem())
 
@@ -1007,9 +1007,6 @@ func isreflexive(t *Type) bool {
 		return false
 
 	case TARRAY:
-		if t.IsSlice() {
-			Fatalf("slice can't be a map key: %v", t)
-		}
 		return isreflexive(t.Elem())
 
 	case TSTRUCT:
@@ -1057,9 +1054,6 @@ func needkeyupdate(t *Type) bool {
 		return true
 
 	case TARRAY:
-		if t.IsSlice() {
-			Fatalf("slice can't be a map key: %v", t)
-		}
 		return needkeyupdate(t.Elem())
 
 	case TSTRUCT:
@@ -1127,7 +1121,6 @@ ok:
 		ot = dextratype(s, ot, t, 0)
 
 	case TARRAY:
-		if t.IsArray() {
 		// ../../../../runtime/type.go:/arrayType
 		s1 := dtypesym(t.Elem())
 		t2 := typSlice(t.Elem())
@@ -1136,19 +1129,18 @@ ok:
 		ot = dsymptr(s, ot, s1, 0)
 		ot = dsymptr(s, ot, s2, 0)
 		ot = duintptr(s, ot, uint64(t.NumElem()))
-		} else {
+		ot = dextratype(s, ot, t, 0)
+
+	case TSLICE:
 		// ../../../../runtime/type.go:/sliceType
 		s1 := dtypesym(t.Elem())
-
 		ot = dcommontype(s, ot, t)
 		ot = dsymptr(s, ot, s1, 0)
-		}
 		ot = dextratype(s, ot, t, 0)
 
-	// ../../../../runtime/type.go:/chanType
 	case TCHAN:
+		// ../../../../runtime/type.go:/chanType
 		s1 := dtypesym(t.Elem())
-
 		ot = dcommontype(s, ot, t)
 		ot = dsymptr(s, ot, s1, 0)
 		ot = duintptr(s, ot, uint64(t.ChanDir()))
@@ -1326,7 +1318,7 @@ ok:
 		// functions must return the existing type structure rather
 		// than creating a new one.
 		switch t.Etype {
-		case TPTR32, TPTR64, TARRAY, TCHAN, TFUNC, TMAP, TSTRUCT:
+		case TPTR32, TPTR64, TARRAY, TCHAN, TFUNC, TMAP, TSLICE, TSTRUCT:
 			keep = true
 		}
 	}
@@ -1654,11 +1646,10 @@ func (p *GCProg) emit(t *Type, offset int64) {
 		p.w.Ptr(offset / int64(Widthptr))
 		p.w.Ptr(offset/int64(Widthptr) + 1)
 
-	case TARRAY:
-		if t.IsSlice() {
+	case TSLICE:
 		p.w.Ptr(offset / int64(Widthptr))
-			return
-		}
+
+	case TARRAY:
 		if t.NumElem() == 0 {
 			// should have been handled by haspointers check above
 			Fatalf("GCProg.emit: empty array")

src/cmd/compile/internal/gc/sinit.go

@@ -1103,13 +1103,13 @@ func anylit(ctxt int, n *Node, var_ *Node, init *Nodes) {
 		structlit(ctxt, 3, n, var_, init)
 
 	case OARRAYLIT:
-		if t.Etype != TARRAY {
-			Fatalf("anylit: not array")
-		}
 		if t.IsSlice() {
 			slicelit(ctxt, n, var_, init)
 			break
 		}
+		if !t.IsArray() {
+			Fatalf("anylit: not array")
+		}
 
 		if var_.isSimpleName() && n.List.Len() > 4 {
 			if ctxt == 0 {
@@ -1414,7 +1414,7 @@ func genAsInitNoCheck(n *Node, reportOnly bool) bool {
 		}
 
 		// nr is the array being converted to a slice
-		if nr.Type == nil || nr.Type.Etype != TARRAY || nr.Type.IsSlice() {
+		if nr.Type == nil || !nr.Type.IsArray() {
 			return false
 		}
 

src/cmd/compile/internal/gc/sizeof_test.go

@@ -41,7 +41,6 @@ func TestSizeof(t *testing.T) {
 		{ChanArgsType{}, 4, 8},
 		{PtrType{}, 4, 8},
 		{SliceType{}, 4, 8},
-		{DDDArrayType{}, 4, 8},
 	}
 
 	for _, tt := range tests {

src/cmd/compile/internal/gc/ssa.go

@@ -1138,7 +1138,7 @@ var opToSSA = map[opAndType]ssa.Op{
 	opAndType{OEQ, TINT64}:     ssa.OpEq64,
 	opAndType{OEQ, TUINT64}:    ssa.OpEq64,
 	opAndType{OEQ, TINTER}:     ssa.OpEqInter,
-	opAndType{OEQ, TARRAY}:     ssa.OpEqSlice,
+	opAndType{OEQ, TSLICE}:     ssa.OpEqSlice,
 	opAndType{OEQ, TFUNC}:      ssa.OpEqPtr,
 	opAndType{OEQ, TMAP}:       ssa.OpEqPtr,
 	opAndType{OEQ, TCHAN}:      ssa.OpEqPtr,
@@ -1158,7 +1158,7 @@ var opToSSA = map[opAndType]ssa.Op{
 	opAndType{ONE, TINT64}:     ssa.OpNeq64,
 	opAndType{ONE, TUINT64}:    ssa.OpNeq64,
 	opAndType{ONE, TINTER}:     ssa.OpNeqInter,
-	opAndType{ONE, TARRAY}:     ssa.OpNeqSlice,
+	opAndType{ONE, TSLICE}:     ssa.OpNeqSlice,
 	opAndType{ONE, TFUNC}:      ssa.OpNeqPtr,
 	opAndType{ONE, TMAP}:       ssa.OpNeqPtr,
 	opAndType{ONE, TCHAN}:      ssa.OpNeqPtr,
@@ -2871,9 +2871,6 @@ func canSSAType(t *Type) bool {
 	}
 	switch t.Etype {
 	case TARRAY:
-		if t.IsSlice() {
-			return true
-		}
 		// We can't do arrays because dynamic indexing is
 		// not supported on SSA variables.
 		// TODO: maybe allow if length is <=1?  All indexes

src/cmd/compile/internal/gc/subr.go

@@ -594,6 +594,7 @@ func methtype(t *Type, mustname int) *Type {
 
 		case TSTRUCT,
 			TARRAY,
+			TSLICE,
 			TMAP,
 			TCHAN,
 			TSTRING,
@@ -641,7 +642,7 @@ func eqtype1(t1, t2 *Type, assumedEqual map[typePair]struct{}) bool {
 	if t1 == t2 {
 		return true
 	}
-	if t1 == nil || t2 == nil || t1.Etype != t2.Etype {
+	if t1 == nil || t2 == nil || t1.Etype != t2.Etype || t1.Broke || t2.Broke {
 		return false
 	}
 	if t1.Sym != nil || t2.Sym != nil {
@@ -836,18 +837,13 @@ func assignop(src *Type, dst *Type, why *string) Op {
 	// 5. src is the predeclared identifier nil and dst is a nillable type.
 	if src.Etype == TNIL {
 		switch dst.Etype {
-		case TARRAY:
-			if !dst.IsSlice() {
-				break
-			}
-			fallthrough
-
 		case TPTR32,
 			TPTR64,
 			TFUNC,
 			TMAP,
 			TCHAN,
-			TINTER:
+			TINTER,
+			TSLICE:
 			return OCONVNOP
 		}
 	}

src/cmd/compile/internal/gc/type.go

@@ -44,6 +44,7 @@ const (
 	TPTR64
 
 	TFUNC
+	TSLICE
 	TARRAY
 	TSTRUCT
 	TCHAN
@@ -70,11 +71,6 @@ const (
 	NTYPE
 )
 
-const (
-	sliceBound = -1   // slices have Bound=sliceBound
-	dddBound   = -100 // arrays declared as [...]T start life with Bound=dddBound
-)
-
 // ChanDir is whether a channel can send, receive, or both.
 type ChanDir uint8
 
@@ -137,7 +133,8 @@ type Type struct {
 	// TCHANARGS: ChanArgsType
 	// TCHAN: *ChanType
 	// TPTR32, TPTR64: PtrType
-	// TARRAY: *ArrayType, SliceType, or DDDArrayType
+	// TARRAY: *ArrayType
+	// TSLICE: SliceType
 	Extra interface{}
 
 	// Width is the width of this Type in bytes.
@@ -273,10 +270,10 @@ func (t *Type) ChanType() *ChanType {
 	return t.Extra.(*ChanType)
 }
 
-// ArrayType contains Type fields specific to array types with known lengths.
+// ArrayType contains Type fields specific to array types.
 type ArrayType struct {
 	Elem        *Type // element type
-	Bound       int64 // number of elements; always >= 0; do not use with sliceBound or dddBound
+	Bound       int64 // number of elements; <0 if unknown yet
 	Haspointers uint8 // 0 unknown, 1 no, 2 yes
 }
 
@@ -285,11 +282,6 @@ type SliceType struct {
 	Elem *Type // element type
 }
 
-// DDDArrayType contains Type fields specific to ddd array types.
-type DDDArrayType struct {
-	Elem *Type // element type
-}
-
 // A Field represents a field in a struct or a method in an interface or
 // associated with a named type.
 type Field struct {
@@ -399,6 +391,9 @@ func typ(et EType) *Type {
 
 // typArray returns a new fixed-length array Type.
 func typArray(elem *Type, bound int64) *Type {
+	if bound < 0 {
+		Fatalf("typArray: invalid bound %v", bound)
+	}
 	t := typ(TARRAY)
 	t.Extra = &ArrayType{Elem: elem, Bound: bound}
 	return t
@@ -406,7 +401,7 @@ func typArray(elem *Type, bound int64) *Type {
 
 // typSlice returns a new slice Type.
 func typSlice(elem *Type) *Type {
-	t := typ(TARRAY)
+	t := typ(TSLICE)
 	t.Extra = SliceType{Elem: elem}
 	return t
 }
@@ -414,7 +409,7 @@ func typSlice(elem *Type) *Type {
 // typDDDArray returns a new [...]T array Type.
 func typDDDArray(elem *Type) *Type {
 	t := typ(TARRAY)
-	t.Extra = DDDArrayType{Elem: elem}
+	t.Extra = &ArrayType{Elem: elem, Bound: -1}
 	return t
 }
 
@@ -519,16 +514,14 @@ func substAny(t *Type, types *[]*Type) *Type {
 		elem := substAny(t.Elem(), types)
 		if elem != t.Elem() {
 			t = t.Copy()
-			switch x := t.Extra.(type) {
-			case *ArrayType:
-				x.Elem = elem
-			case SliceType:
-				t.Extra = SliceType{Elem: elem}
-			case DDDArrayType:
-				t.Extra = DDDArrayType{Elem: elem}
-			default:
-				Fatalf("substAny bad array elem type %T %v", x, t)
+			t.Extra.(*ArrayType).Elem = elem
 		}
+
+	case TSLICE:
+		elem := substAny(t.Elem(), types)
+		if elem != t.Elem() {
+			t = t.Copy()
+			t.Extra = SliceType{Elem: elem}
 		}
 
 	case TCHAN:
@@ -616,11 +609,9 @@ func (t *Type) Copy() *Type {
 		x := *t.Extra.(*ChanType)
 		nt.Extra = &x
 	case TARRAY:
-		if arr, ok := t.Extra.(*ArrayType); ok {
-			x := *arr
+		x := *t.Extra.(*ArrayType)
 		nt.Extra = &x
 	}
-	}
 	// TODO(mdempsky): Find out why this is necessary and explain.
 	if t.Orig == t {
 		nt.Orig = &nt
@@ -735,14 +726,9 @@ func (t *Type) Elem() *Type {
 	case TPTR32, TPTR64:
 		return t.Extra.(PtrType).Elem
 	case TARRAY:
-		switch t := t.Extra.(type) {
-		case *ArrayType:
-			return t.Elem
-		case SliceType:
-			return t.Elem
-		case DDDArrayType:
-			return t.Elem
-		}
+		return t.Extra.(*ArrayType).Elem
+	case TSLICE:
+		return t.Extra.(SliceType).Elem
 	case TCHAN:
 		return t.Extra.(*ChanType).Elem
 	}
@@ -838,8 +824,7 @@ func (t *Type) isDDDArray() bool {
 	if t.Etype != TARRAY {
 		return false
 	}
-	_, ok := t.Extra.(DDDArrayType)
-	return ok
+	return t.Extra.(*ArrayType).Bound < 0
 }
 
 // ArgWidth returns the total aligned argument size for a function.
@@ -982,8 +967,8 @@ func (t *Type) cmp(x *Type) ssa.Cmp {
 		}
 		return t.Val().cmp(x.Val())
 
-	case TPTR32, TPTR64:
-		// No special cases for these two, they are handled
+	case TPTR32, TPTR64, TSLICE:
+		// No special cases for these, they are handled
 		// by the general code after the switch.
 
 	case TSTRUCT:
@@ -1068,7 +1053,7 @@ func (t *Type) cmp(x *Type) ssa.Cmp {
 		panic(e)
 	}
 
-	// Common element type comparison for TARRAY, TCHAN, TPTR32, and TPTR64.
+	// Common element type comparison for TARRAY, TCHAN, TPTR32, TPTR64, and TSLICE.
 	return t.Elem().cmp(x.Elem())
 }
 
@@ -1138,22 +1123,12 @@ func (t *Type) IsChan() bool {
 	return t.Etype == TCHAN
 }
 
-// TODO: Remove noinline when issue 15084 is resolved.
-//go:noinline
 func (t *Type) IsSlice() bool {
-	if t.Etype != TARRAY {
-		return false
-	}
-	_, ok := t.Extra.(SliceType)
-	return ok
+	return t.Etype == TSLICE
 }
 
 func (t *Type) IsArray() bool {
-	if t.Etype != TARRAY {
-		return false
-	}
-	_, ok := t.Extra.(*ArrayType)
-	return ok
+	return t.Etype == TARRAY
 }
 
 func (t *Type) IsStruct() bool {
@@ -1193,41 +1168,23 @@ func (t *Type) FieldName(i int) string {
 
 func (t *Type) NumElem() int64 {
 	t.wantEtype(TARRAY)
-	switch t := t.Extra.(type) {
-	case *ArrayType:
-		return t.Bound
-	case SliceType:
-		return sliceBound
-	case DDDArrayType:
-		return dddBound
-	}
-	Fatalf("NumElem on non-array %T %v", t.Extra, t)
-	return 0
+	at := t.Extra.(*ArrayType)
+	if at.Bound < 0 {
+		Fatalf("NumElem array %v does not have bound yet", t)
+	}
+	return at.Bound
 }
 
 // SetNumElem sets the number of elements in an array type.
-// It should not be used if at all possible.
-// Create a new array/slice/dddArray with typX instead.
-// The only allowed uses are:
-//   * array -> slice as a hack to suppress extra error output
-//   * ddd array -> array
-// TODO(josharian): figure out how to get rid of this entirely.
+// The only allowed use is on array types created with typDDDArray.
+// For other uses, create a new array with typArray instead.
 func (t *Type) SetNumElem(n int64) {
 	t.wantEtype(TARRAY)
-	switch {
-	case n >= 0:
-		if !t.isDDDArray() {
-			Fatalf("SetNumElem non-ddd -> array %v", t)
-		}
-		t.Extra = &ArrayType{Elem: t.Elem(), Bound: n}
-	case n == sliceBound:
-		if !t.IsArray() {
-			Fatalf("SetNumElem non-array -> slice %v", t)
-		}
-		t.Extra = SliceType{Elem: t.Elem()}
-	default:
-		Fatalf("SetNumElem %d %v", n, t)
+	at := t.Extra.(*ArrayType)
+	if at.Bound >= 0 {
+		Fatalf("SetNumElem array %v already has bound %d", t, at.Bound)
 	}
+	at.Bound = n
 }
 
 // ChanDir returns the direction of a channel type t.

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

@@ -76,6 +76,7 @@ var _typekind = []string{
 	TCHAN:       "chan",
 	TMAP:        "map",
 	TARRAY:      "array",
+	TSLICE:      "slice",
 	TFUNC:       "func",
 	TNIL:        "nil",
 	TIDEAL:      "untyped number",
@@ -997,7 +998,7 @@ OpSwitch:
 			n.Type = nil
 			return n
 
-		case TSTRING, TARRAY:
+		case TSTRING, TARRAY, TSLICE:
 			n.Right = indexlit(n.Right)
 			if t.IsString() {
 				n.Type = bytetype
@@ -1005,13 +1006,11 @@ OpSwitch:
 				n.Type = t.Elem()
 			}
 			why := "string"
-			if t.Etype == TARRAY {
 			if t.IsArray() {
 				why = "array"
-				} else {
+			} else if t.IsSlice() {
 				why = "slice"
 			}
-			}
 
 			if n.Right.Type != nil && !n.Right.Type.IsInteger() {
 				Yyerror("non-integer %s index %v", why, n.Right)
@@ -1422,9 +1421,6 @@ OpSwitch:
 			}
 
 		case TARRAY:
-			if t.IsSlice() {
-				break
-			}
 			if callrecv(l) { // has call or receive
 				break
 			}
@@ -1795,13 +1791,7 @@ OpSwitch:
 			n.Type = nil
 			return n
 
-		case TARRAY:
-			if !t.IsSlice() {
-				Yyerror("cannot make type %v", t)
-				n.Type = nil
-				return n
-			}
-
+		case TSLICE:
 			if i >= len(args) {
 				Yyerror("missing len argument to make(%v)", t)
 				n.Type = nil
@@ -2848,19 +2838,19 @@ func indexdup(n *Node, hash map[int64]*Node) {
 	hash[v] = n
 }
 
+// iscomptype reports whether type t is a composite literal type
+// or a pointer to one.
 func iscomptype(t *Type) bool {
-	switch t.Etype {
-	case TARRAY, TSTRUCT, TMAP:
-		return true
-
-	case TPTR32, TPTR64:
-		switch t.Elem().Etype {
-		case TARRAY, TSTRUCT, TMAP:
-			return true
-		}
+	if t.IsPtr() {
+		t = t.Elem()
 	}
 
+	switch t.Etype {
+	case TARRAY, TSLICE, TSTRUCT, TMAP:
+		return true
+	default:
 		return false
+	}
 }
 
 func pushtype(n *Node, t *Type) {
@@ -2943,7 +2933,7 @@ func typecheckcomplit(n *Node) *Node {
 		Yyerror("invalid type for composite literal: %v", t)
 		n.Type = nil
 
-	case TARRAY:
+	case TARRAY, TSLICE:
 		// Only allocate hash if there are some key/value pairs.
 		var hash map[int64]*Node
 		for _, n1 := range n.List.Slice() {
@@ -2954,6 +2944,7 @@ func typecheckcomplit(n *Node) *Node {
 		}
 		length := int64(0)
 		i := 0
+		checkBounds := t.IsArray() && !t.isDDDArray()
 		for i2, n2 := range n.List.Slice() {
 			l := n2
 			setlineno(l)
@@ -2979,11 +2970,10 @@ func typecheckcomplit(n *Node) *Node {
 			i++
 			if int64(i) > length {
 				length = int64(i)
-				if t.IsArray() && length > t.NumElem() {
+				if checkBounds && length > t.NumElem() {
 					setlineno(l)
 					Yyerror("array index %d out of bounds [0:%d]", length-1, t.NumElem())
-					// suppress any further errors out of bounds errors for the same type by pretending it is a slice
-					t.SetNumElem(sliceBound)
+					checkBounds = false
 				}
 			}
 

src/cmd/compile/internal/gc/universe.go

@@ -228,6 +228,7 @@ func typeinit() {
 
 	okforcap[TARRAY] = true
 	okforcap[TCHAN] = true
+	okforcap[TSLICE] = true
 
 	okforconst[TBOOL] = true
 	okforconst[TSTRING] = true
@@ -235,6 +236,7 @@ func typeinit() {
 	okforlen[TARRAY] = true
 	okforlen[TCHAN] = true
 	okforlen[TMAP] = true
+	okforlen[TSLICE] = true
 	okforlen[TSTRING] = true
 
 	okforeq[TPTR32] = true
@@ -246,8 +248,9 @@ func typeinit() {
 	okforeq[TBOOL] = true
 	okforeq[TMAP] = true    // nil only; refined in typecheck
 	okforeq[TFUNC] = true   // nil only; refined in typecheck
-	okforeq[TARRAY] = true  // nil slice only; refined in typecheck
-	okforeq[TSTRUCT] = true // it's complicated; refined in typecheck
+	okforeq[TSLICE] = true  // nil only; refined in typecheck
+	okforeq[TARRAY] = true  // only if element type is comparable; refined in typecheck
+	okforeq[TSTRUCT] = true // only if all struct fields are comparable; refined in typecheck
 
 	okforcmp[TSTRING] = true
 

src/cmd/compile/internal/gc/walk.go

@@ -3125,12 +3125,7 @@ func walkcompare(n *Node, init *Nodes) *Node {
 	default:
 		return n
 
-	case TARRAY:
-		if t.IsSlice() {
-			return n
-		}
-
-	case TSTRUCT:
+	case TARRAY, TSTRUCT:
 		break
 	}