cmd/compile: refactor generic AST walking code

racewalk's "foreach" function applies a function to all of a Node's
immediate children, but with a non-idiomatic signature.

This CL reworks it to recursively iterate over the entire subtree
rooted at Node and provides a way to short-circuit iteration.

Passes toolstash -cmp for std cmd with -race.

Change-Id: I738b73953d608709802c97945b7e0f4e4940d3f4
Reviewed-on: https://go-review.googlesource.com/71911
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/racewalk.go

@@ -452,9 +452,15 @@ func callinstr(np **Node, init *Nodes, wr int, skip int) bool {
 	// that has got a pointer inside. Whether it points to
 	// the heap or not is impossible to know at compile time
 	if class == PAUTOHEAP || class == PEXTERN || b.Op == OINDEX || b.Op == ODOTPTR || b.Op == OIND {
-		hascalls := 0
-		foreach(n, hascallspred, &hascalls)
-		if hascalls != 0 {
+		hasCalls := false
+		inspect(n, func(n *Node) bool {
+			switch n.Op {
+			case OCALL, OCALLFUNC, OCALLMETH, OCALLINTER:
+				hasCalls = true
+			}
+			return !hasCalls
+		})
+		if hasCalls {
 			n = detachexpr(n, init)
 			*np = n
 		}
@@ -542,34 +548,6 @@ func detachexpr(n *Node, init *Nodes) *Node {
 	return ind
 }
 
-func foreachnode(n *Node, f func(*Node, interface{}), c interface{}) {
-	if n != nil {
-		f(n, c)
-	}
-}
-
-func foreachlist(l Nodes, f func(*Node, interface{}), c interface{}) {
-	for _, n := range l.Slice() {
-		foreachnode(n, f, c)
-	}
-}
-
-func foreach(n *Node, f func(*Node, interface{}), c interface{}) {
-	foreachlist(n.Ninit, f, c)
-	foreachnode(n.Left, f, c)
-	foreachnode(n.Right, f, c)
-	foreachlist(n.List, f, c)
-	foreachlist(n.Nbody, f, c)
-	foreachlist(n.Rlist, f, c)
-}
-
-func hascallspred(n *Node, c interface{}) {
-	switch n.Op {
-	case OCALL, OCALLFUNC, OCALLMETH, OCALLINTER:
-		(*c.(*int))++
-	}
-}
-
 // appendinit is like addinit in subr.go
 // but appends rather than prepends.
 func appendinit(np **Node, init Nodes) {

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

@@ -744,3 +744,23 @@ func (n *Nodes) AppendNodes(n2 *Nodes) {
 	}
 	n2.slice = nil
 }
+
+// inspect invokes f on each node in an AST in depth-first order.
+// If f(n) returns false, inspect skips visiting n's children.
+func inspect(n *Node, f func(*Node) bool) {
+	if n == nil || !f(n) {
+		return
+	}
+	inspectList(n.Ninit, f)
+	inspect(n.Left, f)
+	inspect(n.Right, f)
+	inspectList(n.List, f)
+	inspectList(n.Nbody, f)
+	inspectList(n.Rlist, f)
+}
+
+func inspectList(l Nodes, f func(*Node) bool) {
+	for _, n := range l.Slice() {
+		inspect(n, f)
+	}
+}