Add four loops and unless statements

demo1.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	for i := 8; i <= 20; i += 4 {
+		if !(i%8 == 0) {
+			fmt.Println(i, "is not divisible by 8")
+			continue
+		}
+		fmt.Println(i, "is divisible by 8")
+	}
+}

demo2.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	four i := 8; i <= 20; i++ {
+		unless i%8 == 0 {
+			fmt.Println(i, "is not divisible by 8")
+			continue
+		}
+		fmt.Println(i, "is divisible by 8")
+	}
+}
+

demo3.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"fmt"
+)
+
+func f() {
+	fmt.Println("number is divisible by 8")
+}
+
+func g() {
+	fmt.Println("number is not divisible by 8")
+}
+
+func main() {
+	four i := 8; i <= 20; i++ {
+		unless i%8 == 0 {
+			g()
+			continue
+		}
+		f()
+	}
+}

src/cmd/compile/internal/escape/stmt.go

@@ -87,6 +87,19 @@ func (e *escape) stmt(n ir.Node) {
 		e.block(n.Body)
 		e.loopDepth--
 
+	case ir.OFOUR:
+		n := n.(*ir.FourStmt)
+		e.loopDepth++
+		e.discard(n.Cond)
+		e.stmt(n.Post)
+		e.block(n.Body)
+		e.loopDepth--
+
+	case ir.OUNLESS:
+		n := n.(*ir.UnlessStmt)
+		e.discard(n.Cond)
+		e.block(n.Body)
+
 	case ir.ORANGE:
 		// for Key, Value = range X { Body }
 		n := n.(*ir.RangeStmt)

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

@@ -49,6 +49,8 @@ var OpNames = []string{
 	OEQ:               "==",
 	OFALL:             "fallthrough",
 	OFOR:              "for",
+	OFOUR:             "four",
+	OUNLESS:           "unless",
 	OGE:               ">=",
 	OGOTO:             "goto",
 	OGT:               ">",
@@ -279,6 +281,8 @@ var OpPrec = []int{
 	ODEFER:      -1,
 	OFALL:       -1,
 	OFOR:        -1,
+	OFOUR:       -1,
+	OUNLESS:     -1,
 	OGOTO:       -1,
 	OIF:         -1,
 	OLABEL:      -1,
@@ -294,7 +298,7 @@ var OpPrec = []int{
 // StmtWithInit reports whether op is a statement with an explicit init list.
 func StmtWithInit(op Op) bool {
 	switch op {
-	case OIF, OFOR, OSWITCH:
+	case OIF, OFOR, OSWITCH, OFOUR, OUNLESS:
 		return true
 	}
 	return false
@@ -434,6 +438,40 @@ func stmtFmt(n Node, s fmt.State) {
 
 		fmt.Fprintf(s, " { %v }", n.Body)
 
+	case OUNLESS:
+		n := n.(*UnlessStmt)
+		if simpleinit {
+			fmt.Fprintf(s, "unless %v; %v { %v }", n.Init()[0], n.Cond, n.Body)
+		} else {
+			fmt.Fprintf(s, "unless %v { %v }", n.Cond, n.Body)
+		}
+
+	case OFOUR:
+		n := n.(*FourStmt)
+		if !exportFormat { // TODO maybe only if FmtShort, same below
+			fmt.Fprintf(s, "four loop")
+			break
+		}
+
+		fmt.Fprint(s, "four")
+		if simpleinit {
+			fmt.Fprintf(s, " %v;", n.Init()[0])
+		} else if n.Post != nil {
+			fmt.Fprint(s, " ;")
+		}
+
+		if n.Cond != nil {
+			fmt.Fprintf(s, " %v", n.Cond)
+		}
+
+		if n.Post != nil {
+			fmt.Fprintf(s, "; %v", n.Post)
+		} else if simpleinit {
+			fmt.Fprint(s, ";")
+		}
+
+		fmt.Fprintf(s, " { %v }", n.Body)
+
 	case ORANGE:
 		n := n.(*RangeStmt)
 		if !exportFormat {

src/cmd/compile/internal/ir/node.go

@@ -265,6 +265,8 @@ const (
 	ODEFER    // defer Call
 	OFALL     // fallthrough
 	OFOR      // for Init; Cond; Post { Body }
+	OFOUR     // four Init; Cond; Post { Body }
+	OUNLESS   // unless Init; Cond { Body }
 	OGOTO     // goto Label
 	OIF       // if Init; Cond { Then } else { Else }
 	OLABEL    // Label: