cmd/compile: remove DDD array types

Currently we handle [...]T array literals by treating [...]T as
special "DDD array" types. However, these array literals are just
composite literal syntax, not a distinct Go type. Moreover,
representing them as Go types contributes to complexity in a number of
unrelated bits of code.

This CL changes OCOMPLIT typechecking to look for the [...]T syntax
and handle it specially, so we can remove DDD arrays.

Passes toolstash-check.

Change-Id: Ibbf701eac4caa7a321e2d10e256658fdfaa8a160
Reviewed-on: https://go-review.googlesource.com/c/go/+/197604
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -324,13 +324,6 @@ func dowidth(t *types.Type) {
 		if t.Elem() == nil {
 			break
 		}
-		if t.IsDDDArray() {
-			if !t.Broke() {
-				yyerror("use of [...] array outside of array literal")
-				t.SetBroke(true)
-			}
-			break
-		}
 
 		dowidth(t.Elem())
 		if t.Elem().Width != 0 {

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

@@ -720,9 +720,6 @@ func typefmt(t *types.Type, flag FmtFlag, mode fmtMode, depth int) string {
 		return "*" + tmodeString(t.Elem(), mode, depth)
 
 	case TARRAY:
-		if t.IsDDDArray() {
-			return "[...]" + tmodeString(t.Elem(), mode, depth)
-		}
 		return "[" + strconv.FormatInt(t.NumElem(), 10) + "]" + tmodeString(t.Elem(), mode, depth)
 
 	case TSLICE:

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

@@ -62,7 +62,6 @@ const (
 	ctxCallee              // call-only expressions are ok
 	ctxMultiOK             // multivalue function returns are ok
 	ctxAssign              // assigning to expression
-	ctxCompLit             // type in composite literal
 )
 
 // type checks the whole tree of an expression.
@@ -413,15 +412,12 @@ func typecheck1(n *Node, top int) (res *Node) {
 		if n.Left == nil {
 			t = types.NewSlice(r.Type)
 		} else if n.Left.Op == ODDD {
-			if top&ctxCompLit == 0 {
 			if !n.Diag() {
 				n.SetDiag(true)
 				yyerror("use of [...] array outside of array literal")
 			}
 			n.Type = nil
 			return n
-			}
-			t = types.NewDDDArray(r.Type)
 		} else {
 			n.Left = indexlit(typecheck(n.Left, ctxExpr))
 			l := n.Left
@@ -457,9 +453,7 @@ func typecheck1(n *Node, top int) (res *Node) {
 		setTypeNode(n, t)
 		n.Left = nil
 		n.Right = nil
-		if !t.IsDDDArray() {
 		checkwidth(t)
-		}
 
 	case OTMAP:
 		ok |= ctxType
@@ -517,7 +511,7 @@ func typecheck1(n *Node, top int) (res *Node) {
 
 	// type or expr
 	case ODEREF:
-		n.Left = typecheck(n.Left, ctxExpr|ctxType|top&ctxCompLit)
+		n.Left = typecheck(n.Left, ctxExpr|ctxType)
 		l := n.Left
 		t := l.Type
 		if t == nil {
@@ -527,13 +521,9 @@ func typecheck1(n *Node, top int) (res *Node) {
 		if l.Op == OTYPE {
 			ok |= ctxType
 			setTypeNode(n, types.NewPtr(l.Type))
+			n.Left = nil
 			// Ensure l.Type gets dowidth'd for the backend. Issue 20174.
-			// Don't checkwidth [...] arrays, though, since they
-			// will be replaced by concrete-sized arrays. Issue 20333.
-			if !l.Type.IsDDDArray() {
 			checkwidth(l.Type)
-			}
-			n.Left = nil
 			break
 		}
 
@@ -1257,7 +1247,7 @@ func typecheck1(n *Node, top int) (res *Node) {
 		n.Left = defaultlit(n.Left, nil)
 		l = n.Left
 		if l.Op == OTYPE {
-			if n.IsDDD() || l.Type.IsDDDArray() {
+			if n.IsDDD() {
 				if !l.Type.Broke() {
 					yyerror("invalid use of ... in type conversion to %v", l.Type)
 				}
@@ -2777,17 +2767,33 @@ func typecheckcomplit(n *Node) (res *Node) {
 	}
 
 	// Save original node (including n.Right)
-	norig := n.copy()
+	n.Orig = n.copy()
 
 	setlineno(n.Right)
-	n.Right = typecheck(n.Right, ctxType|ctxCompLit)
-	l := n.Right // sic
-	t := l.Type
+
+	// Need to handle [...]T arrays specially.
+	if n.Right.Op == OTARRAY && n.Right.Left != nil && n.Right.Left.Op == ODDD {
+		n.Right.Right = typecheck(n.Right.Right, ctxType)
+		if n.Right.Right.Type == nil {
+			n.Type = nil
+			return n
+		}
+		elemType := n.Right.Right.Type
+
+		length := typecheckarraylit(elemType, -1, n.List.Slice())
+
+		n.Op = OARRAYLIT
+		n.Type = types.NewArray(elemType, length)
+		n.Right = nil
+		return n
+	}
+
+	n.Right = typecheck(n.Right, ctxType)
+	t := n.Right.Type
 	if t == nil {
 		n.Type = nil
 		return n
 	}
-	nerr := nerrors
 	n.Type = t
 
 	switch t.Etype {
@@ -2796,12 +2802,7 @@ func typecheckcomplit(n *Node) (res *Node) {
 		n.Type = nil
 
 	case TARRAY:
-		if t.IsDDDArray() {
-			length := typecheckarraylit(t.Elem(), -1, n.List.Slice())
-			t.SetNumElem(length)
-		} else {
 		typecheckarraylit(t.Elem(), t.NumElem(), n.List.Slice())
-		}
 		n.Op = OARRAYLIT
 		n.Right = nil
 
@@ -2954,11 +2955,6 @@ func typecheckcomplit(n *Node) (res *Node) {
 		n.Right = nil
 	}
 
-	if nerr != nerrors {
-		return n
-	}
-
-	n.Orig = norig
 	return n
 }
 

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

@@ -495,14 +495,6 @@ func NewSlice(elem *Type) *Type {
 	return t
 }
 
-// NewDDDArray returns a new [...]T array Type.
-func NewDDDArray(elem *Type) *Type {
-	t := New(TARRAY)
-	t.Extra = &Array{Elem: elem, Bound: -1}
-	t.SetNotInHeap(elem.NotInHeap())
-	return t
-}
-
 // NewChan returns a new chan Type with direction dir.
 func NewChan(elem *Type, dir ChanDir) *Type {
 	t := New(TCHAN)
@@ -882,13 +874,6 @@ func (t *Type) SetInterface(methods []*Field) {
 	t.Methods().Set(methods)
 }
 
-func (t *Type) IsDDDArray() bool {
-	if t.Etype != TARRAY {
-		return false
-	}
-	return t.Extra.(*Array).Bound < 0
-}
-
 func (t *Type) WidthCalculated() bool {
 	return t.Align > 0
 }
@@ -1325,23 +1310,7 @@ func (t *Type) FieldName(i int) string {
 
 func (t *Type) NumElem() int64 {
 	t.wantEtype(TARRAY)
-	at := t.Extra.(*Array)
-	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.
-// The only allowed use is on array types created with NewDDDArray.
-// For other uses, create a new array with NewArray instead.
-func (t *Type) SetNumElem(n int64) {
-	t.wantEtype(TARRAY)
-	at := t.Extra.(*Array)
-	if at.Bound >= 0 {
-		Fatalf("SetNumElem array %v already has bound %d", t, at.Bound)
-	}
-	at.Bound = n
+	return t.Extra.(*Array).Bound
 }
 
 type componentsIncludeBlankFields bool