[dev.typeparams] cmd/compile: formalize "hidden parameters" idea

This CL formalizes the closure-var trick used for method-value
wrappers to be reusable for defining other functions that take hidden
parameters via the closure-context register. In particular, it:

1. Adds a new ir.NewHiddenParam function for creating hidden
parameters.

2. Changes ir.NewClosureVar to copy Type/Typecheck from the closure
variable, so that callers can needing to manually copy these.

3. Updates existing code accordingly (i.e., method-value wrappers to
start using ir.NewHiddenParam, and closure builders to stop copying
types).

Longer term, I anticipate using this to pass dictionaries to stenciled
functions within unified IR.

Change-Id: I9da3ffdb2a26d15c6e89a21b4e080686d6dc872c
Reviewed-on: https://go-review.googlesource.com/c/go/+/332612
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>

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

@@ -343,9 +343,7 @@ func (e *escape) wrapExpr(pos src.XPos, exprp *ir.Node, init *ir.Nodes, call ir.
 
 		e.oldLoc(tmp).captured = true
 
-		cv := ir.NewClosureVar(pos, wrapper, tmp)
-		cv.SetType(tmp.Type())
-		tmp = typecheck.Expr(cv).(*ir.Name)
+		tmp = ir.NewClosureVar(pos, wrapper, tmp)
 	}
 
 	*exprp = tmp

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

@@ -183,9 +183,15 @@ func (b *batch) initFunc(fn *ir.Func) {
 
 	// Allocate locations for local variables.
 	for _, n := range fn.Dcl {
-		if n.Op() == ir.ONAME {
 		e.newLoc(n, false)
 	}
+
+	// Also for hidden parameters (e.g., the ".this" parameter to a
+	// method value wrapper).
+	if fn.OClosure == nil {
+		for _, n := range fn.ClosureVars {
+			e.newLoc(n.Canonical(), false)
+		}
 	}
 
 	// Initialize resultIndex for result parameters.

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

@@ -46,9 +46,6 @@ func (e *escape) exprSkipInit(k hole, n ir.Node) {
 		if n.Class == ir.PFUNC || n.Class == ir.PEXTERN {
 			return
 		}
-		if n.IsClosureVar() && n.Defn == nil {
-			return // ".this" from method value wrapper
-		}
 		e.flow(k, e.oldLoc(n))
 
 	case ir.OPLUS, ir.ONEG, ir.OBITNOT, ir.ONOT:

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

@@ -222,7 +222,9 @@ func (e *escape) newLoc(n ir.Node, transient bool) *location {
 	}
 
 	if n != nil && n.Op() == ir.ONAME {
-		n = n.(*ir.Name).Canonical()
+		if canon := n.(*ir.Name).Canonical(); n != canon {
+			base.Fatalf("newLoc on non-canonical %v (canonical is %v)", n, canon)
+		}
 	}
 	loc := &location{
 		n:         n,
@@ -234,7 +236,9 @@ func (e *escape) newLoc(n ir.Node, transient bool) *location {
 	if n != nil {
 		if n.Op() == ir.ONAME {
 			n := n.(*ir.Name)
-			if n.Curfn != e.curfn {
+			if n.Class == ir.PPARAM && n.Curfn == nil {
+				// ok; hidden parameter
+			} else if n.Curfn != e.curfn {
 				base.Fatalf("curfn mismatch: %v != %v for %v", n.Curfn, e.curfn, n)
 			}
 

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

@@ -358,7 +358,7 @@ func (n *Name) Byval() bool {
 	return n.Canonical().flags&nameByval != 0
 }
 
-// NewClosureVar creates a new closure variable for fn to refer to
+// NewClosureVar returns 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())
@@ -368,11 +368,33 @@ func NewClosureVar(pos src.XPos, fn *Func, n *Name) *Name {
 	c.Defn = n.Canonical()
 	c.Outer = n
 
+	c.SetType(n.Type())
+	c.SetTypecheck(n.Typecheck())
+
 	fn.ClosureVars = append(fn.ClosureVars, c)
 
 	return c
 }
 
+// NewHiddenParam returns a new hidden parameter for fn with the given
+// name and type.
+func NewHiddenParam(pos src.XPos, fn *Func, sym *types.Sym, typ *types.Type) *Name {
+	if fn.OClosure != nil {
+		base.FatalfAt(fn.Pos(), "cannot add hidden parameters to closures")
+	}
+
+	fn.SetNeedctxt(true)
+
+	// Create a fake parameter, disassociated from any real function, to
+	// pretend to capture.
+	fake := NewNameAt(pos, sym)
+	fake.Class = PPARAM
+	fake.SetType(typ)
+	fake.SetByval(true)
+
+	return NewClosureVar(pos, fn, fake)
+}
+
 // 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 the closure

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

@@ -1623,11 +1623,7 @@ func (r *reader) funcLit() ir.Node {
 
 	fn.ClosureVars = make([]*ir.Name, 0, r.len())
 	for len(fn.ClosureVars) < cap(fn.ClosureVars) {
-		pos := r.pos()
-		outer := r.useLocal()
-
-		cv := ir.NewClosureVar(pos, fn, outer)
-		r.setType(cv, outer.Type())
+		ir.NewClosureVar(r.pos(), fn, r.useLocal())
 	}
 
 	r.addBody(fn)
@@ -2204,17 +2200,10 @@ func (r *reader) methodValueWrapper(tbase *types.Type, method *types.Field, targ
 	pos := base.AutogeneratedPos
 
 	fn := r.newWrapperFunc(pos, sym, nil, method)
-	fn.SetNeedctxt(true)
 	sym.Def = fn
 
 	// Declare and initialize variable holding receiver.
-	recv := ir.NewNameAt(pos, typecheck.Lookup(".this"))
-	recv.Class = ir.PAUTOHEAP
-	recv.SetType(recvType)
-	recv.Curfn = fn
-	recv.SetIsClosureVar(true)
-	recv.SetByval(true)
-	fn.ClosureVars = append(fn.ClosureVars, recv)
+	recv := ir.NewHiddenParam(pos, fn, typecheck.Lookup(".this"), recvType)
 
 	addTailCall(pos, fn, recv, method)
 

src/cmd/compile/internal/typecheck/iimport.go

@@ -1289,14 +1289,9 @@ func (r *importReader) node() ir.Node {
 		cvars := make([]*ir.Name, r.int64())
 		for i := range cvars {
 			cvars[i] = ir.CaptureName(r.pos(), fn, r.localName().Canonical())
-			if go117ExportTypes {
-				if cvars[i].Type() != nil || cvars[i].Defn == nil {
+			if go117ExportTypes && cvars[i].Defn == nil {
 				base.Fatalf("bad import of closure variable")
 			}
-				// Closure variable should have Defn set, which is its captured
-				// variable, and it gets the same type as the captured variable.
-				cvars[i].SetType(cvars[i].Defn.Type())
-			}
 		}
 		fn.ClosureVars = cvars
 		r.allClosureVars = append(r.allClosureVars, cvars...)

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

@@ -238,17 +238,10 @@ func methodValueWrapper(dot *ir.SelectorExpr) *ir.Func {
 
 	fn := typecheck.DeclFunc(sym, tfn)
 	fn.SetDupok(true)
-	fn.SetNeedctxt(true)
 	fn.SetWrapper(true)
 
 	// Declare and initialize variable holding receiver.
-	ptr := ir.NewNameAt(base.Pos, typecheck.Lookup(".this"))
-	ptr.Class = ir.PAUTOHEAP
-	ptr.SetType(rcvrtype)
-	ptr.Curfn = fn
-	ptr.SetIsClosureVar(true)
-	ptr.SetByval(true)
-	fn.ClosureVars = append(fn.ClosureVars, ptr)
+	ptr := ir.NewHiddenParam(base.Pos, fn, typecheck.Lookup(".this"), rcvrtype)
 
 	call := ir.NewCallExpr(base.Pos, ir.OCALL, ir.NewSelectorExpr(base.Pos, ir.OXDOT, ptr, meth), nil)
 	call.Args = ir.ParamNames(tfn.Type())