cmd/compile, runtime: eliminate growslice_n

Fixes #11419.

Change-Id: I7935a253e3e96191a33f5041bab203ecc5f0c976
Reviewed-on: https://go-review.googlesource.com/20647Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -128,7 +128,6 @@ const runtimeimport = "" +
 	"func @\"\".block ()\n" +
 	"func @\"\".makeslice (@\"\".typ·2 *byte, @\"\".nel·3 int64, @\"\".cap·4 int64) (@\"\".ary·1 []any)\n" +
 	"func @\"\".growslice (@\"\".typ·2 *byte, @\"\".old·3 []any, @\"\".cap·4 int) (@\"\".ary·1 []any)\n" +
-	"func @\"\".growslice_n (@\"\".typ·2 *byte, @\"\".old·3 []any, @\"\".n·4 int) (@\"\".ary·1 []any)\n" +
 	"func @\"\".memmove (@\"\".to·1 *any, @\"\".frm·2 *any, @\"\".length·3 uintptr \"unsafe-uintptr\")\n" +
 	"func @\"\".memclr (@\"\".ptr·1 *byte, @\"\".length·2 uintptr \"unsafe-uintptr\")\n" +
 	"func @\"\".memequal (@\"\".x·2 *any, @\"\".y·3 *any, @\"\".size·4 uintptr \"unsafe-uintptr\") (? bool)\n" +

src/cmd/compile/internal/gc/builtin/runtime.go

@@ -165,7 +165,6 @@ func block()
 
 func makeslice(typ *byte, nel int64, cap int64) (ary []any)
 func growslice(typ *byte, old []any, cap int) (ary []any)
-func growslice_n(typ *byte, old []any, n int) (ary []any)
 func memmove(to *any, frm *any, length uintptr)
 func memclr(ptr *byte, length uintptr)
 

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

@@ -2777,10 +2777,12 @@ func addstr(n *Node, init *Nodes) *Node {
 // expand append(l1, l2...) to
 //   init {
 //     s := l1
-//     if n := len(l1) + len(l2) - cap(s); n > 0 {
-//       s = growslice_n(s, n)
+//     n := len(s) + len(l2)
+//     // Compare as uint so growslice can panic on overflow.
+//     if uint(n) > uint(cap(s)) {
+//       s = growslice(s, n)
 //     }
-//     s = s[:len(l1)+len(l2)]
+//     s = s[:n]
 //     memmove(&s[len(l1)], &l2[0], len(l2)*sizeof(T))
 //   }
 //   s
@@ -2800,33 +2802,38 @@ func appendslice(n *Node, init *Nodes) *Node {
 	l1 := n.List.First()
 	l2 := n.List.Second()
 
-	s := temp(l1.Type) // var s []T
 	var l []*Node
+
+	// var s []T
+	s := temp(l1.Type)
 	l = append(l, Nod(OAS, s, l1)) // s = l1
 
-	nt := temp(Types[TINT])
+	// n := len(s) + len(l2)
+	nn := temp(Types[TINT])
+	l = append(l, Nod(OAS, nn, Nod(OADD, Nod(OLEN, s, nil), Nod(OLEN, l2, nil))))
 
+	// if uint(n) > uint(cap(s))
 	nif := Nod(OIF, nil, nil)
+	nif.Left = Nod(OGT, Nod(OCONV, nn, nil), Nod(OCONV, Nod(OCAP, s, nil), nil))
+	nif.Left.Left.Type = Types[TUINT]
+	nif.Left.Right.Type = Types[TUINT]
 
-	// n := len(s) + len(l2) - cap(s)
-	nif.Ninit.Set1(Nod(OAS, nt, Nod(OSUB,
-		Nod(OADD, Nod(OLEN, s, nil), Nod(OLEN, l2, nil)),
-		Nod(OCAP, s, nil))))
-
-	nif.Left = Nod(OGT, nt, Nodintconst(0))
-
-	// instantiate growslice_n(Type*, []any, int) []any
-	fn := syslook("growslice_n") //   growslice_n(<type>, old []T, n int64) (ret []T)
+	// instantiate growslice(Type*, []any, int) []any
+	fn := syslook("growslice")
 	substArgTypes(&fn, s.Type.Type, s.Type.Type)
 
-	// s = growslice_n(T, s, n)
-	nif.Nbody.Set1(Nod(OAS, s, mkcall1(fn, s.Type, &nif.Ninit, typename(s.Type), s, nt)))
-
+	// s = growslice(T, s, n)
+	nif.Nbody.Set1(Nod(OAS, s, mkcall1(fn, s.Type, &nif.Ninit, typename(s.Type), s, nn)))
 	l = append(l, nif)
 
+	// s = s[:n]
+	nt := Nod(OSLICE, s, Nod(OKEY, nil, nn))
+	nt.Etype = 1
+	l = append(l, Nod(OAS, s, nt))
+
 	if haspointers(l1.Type.Type) {
-		// copy(s[len(l1):len(l1)+len(l2)], l2)
-		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), Nod(OADD, Nod(OLEN, l1, nil), Nod(OLEN, l2, nil))))
+		// copy(s[len(l1):], l2)
+		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))
 
 		nptr1.Etype = 1
 		nptr2 := l2
@@ -2838,8 +2845,8 @@ func appendslice(n *Node, init *Nodes) *Node {
 		l = append(ln.Slice(), nt)
 	} else if instrumenting {
 		// rely on runtime to instrument copy.
-		// copy(s[len(l1):len(l1)+len(l2)], l2)
-		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), Nod(OADD, Nod(OLEN, l1, nil), Nod(OLEN, l2, nil))))
+		// copy(s[len(l1):], l2)
+		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))
 
 		nptr1.Etype = 1
 		nptr2 := l2
@@ -2857,8 +2864,8 @@ func appendslice(n *Node, init *Nodes) *Node {
 	} else {
 		// memmove(&s[len(l1)], &l2[0], len(l2)*sizeof(T))
 		nptr1 := Nod(OINDEX, s, Nod(OLEN, l1, nil))
-
 		nptr1.Bounded = true
+
 		nptr1 = Nod(OADDR, nptr1, nil)
 
 		nptr2 := Nod(OSPTR, l2, nil)
@@ -2875,13 +2882,6 @@ func appendslice(n *Node, init *Nodes) *Node {
 		l = append(ln.Slice(), nt)
 	}
 
-	// s = s[:len(l1)+len(l2)]
-	nt = Nod(OADD, Nod(OLEN, l1, nil), Nod(OLEN, l2, nil))
-
-	nt = Nod(OSLICE, s, Nod(OKEY, nil, nt))
-	nt.Etype = 1
-	l = append(l, Nod(OAS, s, nt))
-
 	typechecklist(l, Etop)
 	walkstmtlist(l)
 	init.Append(l...)

src/runtime/slice.go

@@ -33,17 +33,6 @@ func makeslice(t *slicetype, len64, cap64 int64) slice {
 	return slice{p, len, cap}
 }
 
-// growslice_n is a variant of growslice that takes the number of new elements
-// instead of the new minimum capacity.
-// TODO(rsc): This is used by append(slice, slice...).
-// The compiler should change that code to use growslice directly (issue #11419).
-func growslice_n(t *slicetype, old slice, n int) slice {
-	if n < 1 {
-		panic(errorString("growslice: invalid n"))
-	}
-	return growslice(t, old, old.cap+n)
-}
-
 // growslice handles slice growth during append.
 // It is passed the slice type, the old slice, and the desired new minimum capacity,
 // and it returns a new slice with at least that capacity, with the old data