[dev.typeparams] cmd/compile: refactor CaptureName

CaptureName currently does a few things: checks if a variable needs to
be captured at all; checks if the variable has already been captured;
and creates and saves a new variable. This full suite of functionality
is useful for noder and irgen, but unified IR and other backend code
only has a need for the last feature.

This CL refactors CaptureName a little bit and extracts out
NewClosureVar as a function usable for callers that don't need the
extra features of CaptureName.

Change-Id: I8a67c6375e44babe53344bf78e335535c57f9607
Reviewed-on: https://go-review.googlesource.com/c/go/+/330193
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.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>

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

@@ -358,39 +358,52 @@ func (n *Name) Byval() bool {
 	return n.Canonical().flags&nameByval != 0
 }
 
+// NewClosureVar creates a new closure variable for fn to refer to
+// outer variable n.
+func NewClosureVar(pos src.XPos, fn *Func, n *Name) *Name {
+	c := NewNameAt(pos, n.Sym())
+	c.Curfn = fn
+	c.Class = PAUTOHEAP
+	c.SetIsClosureVar(true)
+	c.Defn = n.Canonical()
+	c.Outer = n
+
+	fn.ClosureVars = append(fn.ClosureVars, c)
+
+	return c
+}
+
 // CaptureName returns a Name suitable for referring to n from within function
 // fn or from the package block if fn is nil. If n is a free variable declared
-// within a function that encloses fn, then CaptureName returns a closure
-// variable that refers to n and adds it to fn.ClosureVars. Otherwise, it simply
-// returns n.
+// within a function that encloses fn, then CaptureName returns the closure
+// variable that refers to n within fn, creating it if necessary.
+// Otherwise, it simply returns n.
 func CaptureName(pos src.XPos, fn *Func, n *Name) *Name {
+	if n.Op() != ONAME || n.Curfn == nil {
+		return n // okay to use directly
+	}
 	if n.IsClosureVar() {
 		base.FatalfAt(pos, "misuse of CaptureName on closure variable: %v", n)
 	}
-	if n.Op() != ONAME || n.Curfn == nil || n.Curfn == fn {
-		return n // okay to use directly
+
+	c := n.Innermost
+	if c == nil {
+		c = n
 	}
+	if c.Curfn == fn {
+		return c
+	}
+
 	if fn == nil {
 		base.FatalfAt(pos, "package-block reference to %v, declared in %v", n, n.Curfn)
 	}
 
-	c := n.Innermost
-	if c != nil && c.Curfn == fn {
-		return c
-	}
-
 	// Do not have a closure var for the active closure yet; make one.
-	c = NewNameAt(pos, n.Sym())
-	c.Curfn = fn
-	c.Class = PAUTOHEAP
-	c.SetIsClosureVar(true)
-	c.Defn = n
+	c = NewClosureVar(pos, fn, c)
 
 	// Link into list of active closure variables.
 	// Popped from list in FinishCaptureNames.
-	c.Outer = n.Innermost
 	n.Innermost = c
-	fn.ClosureVars = append(fn.ClosureVars, c)
 
 	return c
 }

src/cmd/compile/internal/noder/reader.go

@@ -1558,20 +1558,13 @@ func (r *reader) funcLit() ir.Node {
 		fn.Nname.Ntype = ir.TypeNodeAt(typPos, xtype2)
 	}
 
-	fn.ClosureVars = make([]*ir.Name, r.len())
-	for i := range fn.ClosureVars {
+	fn.ClosureVars = make([]*ir.Name, 0, r.len())
+	for len(fn.ClosureVars) < cap(fn.ClosureVars) {
 		pos := r.pos()
 		outer := r.useLocal()
 
-		cv := ir.NewNameAt(pos, outer.Sym())
+		cv := ir.NewClosureVar(pos, fn, outer)
 		r.setType(cv, outer.Type())
-		cv.Curfn = fn
-		cv.Class = ir.PAUTOHEAP
-		cv.SetIsClosureVar(true)
-		cv.Defn = outer.Canonical()
-		cv.Outer = outer
-
-		fn.ClosureVars[i] = cv
 	}
 
 	r.addBody(fn)