[dev.typeparams] cmd/compile: refactor closure construction

typecheck.tcClosure is complicated with many code flows because all of
its callers setup the closure funcs in slightly different ways. E.g.,
it's non-obvious who's responsible for setting the underlying func's
Sym or adding it to target.Decls, or how to write new code that
constructs a closure without interfering with existing code.

This CL refactors everything to use three common functions in package
ir: NewClosureFunc (which handle creating the Func, Name, and
ClosureExpr and wiring them together), NameClosure (which generates
and assigns its unique Sym), and UseClosure (which handles adding the
Func to target.Decls).

Most IR builders can actually name the closure right away, but the
legacy noder+typecheck path may not yet know the name of the enclosing
function. In particular, for methods declared with aliased receiver
parameters, we need to wait until after typechecking top-level
declarations to know the method's true name. So they're left anonymous
until typecheck.

UseClosure does relatively little work today, but it serves as a
useful spot to check that the code setting up closures got it right.
It may also eventually serve as an optimization point for early
lifting of trivial closures, which may or may not ultimately be
beneficial.

Change-Id: I7da1e93c70d268f575b12d6aaeb2336eb910a6f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/327051
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

1 files changed, 34 insertions, 35 deletions

diff --git a/src/cmd/compile/internal/noder/noder.go b/src/cmd/compile/internal/noder/noder.go
index 9dc05182d1..ced3f32a53 100644
--- a/src/cmd/compile/internal/noder/noder.go
+++ b/src/cmd/compile/internal/noder/noder.go
@@ -110,25 +110,35 @@ func LoadPackage(filenames []string) {
 	//   We also defer type alias declarations until phase 2
 	//   to avoid cycles like #18640.
 	//   TODO(gri) Remove this again once we have a fix for #25838.
-
-	// Don't use range--typecheck can add closures to Target.Decls.
-	base.Timer.Start("fe", "typecheck", "top1")
-	for i := 0; i < len(typecheck.Target.Decls); i++ {
-		n := typecheck.Target.Decls[i]
-		if op := n.Op(); op != ir.ODCL && op != ir.OAS && op != ir.OAS2 && (op != ir.ODCLTYPE || !n.(*ir.Decl).X.Alias()) {
-			typecheck.Target.Decls[i] = typecheck.Stmt(n)
-		}
-	}
-
+	//
 	// Phase 2: Variable assignments.
 	//   To check interface assignments, depends on phase 1.
 
 	// Don't use range--typecheck can add closures to Target.Decls.
-	base.Timer.Start("fe", "typecheck", "top2")
-	for i := 0; i < len(typecheck.Target.Decls); i++ {
-		n := typecheck.Target.Decls[i]
-		if op := n.Op(); op == ir.ODCL || op == ir.OAS || op == ir.OAS2 || op == ir.ODCLTYPE && n.(*ir.Decl).X.Alias() {
-			typecheck.Target.Decls[i] = typecheck.Stmt(n)
+	for phase, name := range []string{"top1", "top2"} {
+		base.Timer.Start("fe", "typecheck", name)
+		for i := 0; i < len(typecheck.Target.Decls); i++ {
+			n := typecheck.Target.Decls[i]
+			op := n.Op()
+
+			// Closure function declarations are typechecked as part of the
+			// closure expression.
+			if fn, ok := n.(*ir.Func); ok && fn.OClosure != nil {
+				continue
+			}
+
+			// We don't actually add ir.ODCL nodes to Target.Decls. Make sure of that.
+			if op == ir.ODCL {
+				base.FatalfAt(n.Pos(), "unexpected top declaration: %v", op)
+			}
+
+			// Identify declarations that should be deferred to the second
+			// iteration.
+			late := op == ir.OAS || op == ir.OAS2 || op == ir.ODCLTYPE && n.(*ir.Decl).X.Alias()
+
+			if late == (phase == 1) {
+				typecheck.Target.Decls[i] = typecheck.Stmt(n)
+			}
 		}
 	}
 
@@ -137,16 +147,15 @@ func LoadPackage(filenames []string) {
 	base.Timer.Start("fe", "typecheck", "func")
 	var fcount int64
 	for i := 0; i < len(typecheck.Target.Decls); i++ {
-		n := typecheck.Target.Decls[i]
-		if n.Op() == ir.ODCLFUNC {
+		if fn, ok := typecheck.Target.Decls[i].(*ir.Func); ok {
 			if base.Flag.W > 1 {
-				s := fmt.Sprintf("\nbefore typecheck %v", n)
-				ir.Dump(s, n)
+				s := fmt.Sprintf("\nbefore typecheck %v", fn)
+				ir.Dump(s, fn)
 			}
-			typecheck.FuncBody(n.(*ir.Func))
+			typecheck.FuncBody(fn)
 			if base.Flag.W > 1 {
-				s := fmt.Sprintf("\nafter typecheck %v", n)
-				ir.Dump(s, n)
+				s := fmt.Sprintf("\nafter typecheck %v", fn)
+				ir.Dump(s, fn)
 			}
 			fcount++
 		}
@@ -1794,24 +1803,14 @@ func fakeRecv() *ir.Field {
 }
 
 func (p *noder) funcLit(expr *syntax.FuncLit) ir.Node {
-	xtype := p.typeExpr(expr.Type)
-
-	fn := ir.NewFunc(p.pos(expr))
-	fn.SetIsHiddenClosure(ir.CurFunc != nil)
-
-	fn.Nname = ir.NewNameAt(p.pos(expr), ir.BlankNode.Sym()) // filled in by tcClosure
-	fn.Nname.Func = fn
-	fn.Nname.Ntype = xtype
-	fn.Nname.Defn = fn
-
-	clo := ir.NewClosureExpr(p.pos(expr), fn)
-	fn.OClosure = clo
+	fn := ir.NewClosureFunc(p.pos(expr), ir.CurFunc)
+	fn.Nname.Ntype = p.typeExpr(expr.Type)
 
 	p.funcBody(fn, expr.Body)
 
 	ir.FinishCaptureNames(base.Pos, ir.CurFunc, fn)
 
-	return clo
+	return fn.OClosure
 }
 
 // A function named init is a special case.