cmd/compile: eliminate PPARAMREF

As in the elimination of PHEAP|PPARAM in CL 23393,
this is something the front end can trivially take care of
and then not bother the back ends with.
It also eliminates some suspect (and only lightly exercised)
code paths in the back ends.

I don't have a smoking gun for this one but it seems
more clearly correct.

Change-Id: I3b3f5e669b3b81d091ff1e2fb13226a6f14c69d5
Reviewed-on: https://go-review.googlesource.com/23431Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/compile/internal/arm/gsubr.go

@@ -86,17 +86,8 @@ func split64(n *gc.Node, lo *gc.Node, hi *gc.Node) {
 
 			n = &n1
 
-		case gc.ONAME:
-			if n.Class == gc.PPARAMREF {
-				var n1 gc.Node
-				gc.Cgen(n.Name.Heapaddr, &n1)
-				sclean[nsclean-1] = n1
-				n = &n1
-			}
-
+		case gc.ONAME, gc.OINDREG:
 			// nothing
-		case gc.OINDREG:
-			break
 		}
 
 		*lo = *n

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

@@ -518,8 +518,7 @@ func cgen_wb(n, res *Node, wb bool) {
 	case ODOT,
 		ODOTPTR,
 		OINDEX,
-		OIND,
-		ONAME: // PPARAMREF var
+		OIND:
 		var n1 Node
 		Igen(n, &n1, res)
 
@@ -1545,6 +1544,7 @@ func Agen(n *Node, res *Node) {
 
 	switch n.Op {
 	default:
+		Dump("bad agen", n)
 		Fatalf("agen: unknown op %v", Nconv(n, FmtShort|FmtSign))
 
 	case OCALLMETH:
@@ -1571,24 +1571,6 @@ func Agen(n *Node, res *Node) {
 		Thearch.Gmove(&n1, res)
 		Regfree(&n1)
 
-	case ONAME:
-		// should only get here with names in this func.
-		if n.Name.Funcdepth > 0 && n.Name.Funcdepth != Funcdepth {
-			Dump("bad agen", n)
-			Fatalf("agen: bad ONAME funcdepth %d != %d", n.Name.Funcdepth, Funcdepth)
-		}
-
-		// should only get here for heap vars or paramref
-		if n.Class != PPARAMREF {
-			Dump("bad agen", n)
-			Fatalf("agen: bad ONAME class %#x", n.Class)
-		}
-
-		Cgen(n.Name.Heapaddr, res)
-		if n.Xoffset != 0 {
-			addOffset(res, n.Xoffset)
-		}
-
 	case OIND:
 		Cgen(nl, res)
 		if !nl.NonNil {
@@ -1646,8 +1628,9 @@ func Igen(n *Node, a *Node, res *Node) {
 
 	switch n.Op {
 	case ONAME:
-		if n.Class == PPARAMREF {
-			break
+		if n.Class == PAUTOHEAP {
+			Dump("igen", n)
+			Fatalf("bad name")
 		}
 		*a = *n
 		return
@@ -1702,11 +1685,11 @@ func Igen(n *Node, a *Node, res *Node) {
 		a.Type = n.Type
 		return
 
-		// Index of fixed-size array by constant can
-	// put the offset in the addressing.
-	// Could do the same for slice except that we need
-	// to use the real index for the bounds checking.
 	case OINDEX:
+		// Index of fixed-size array by constant can
+		// put the offset in the addressing.
+		// Could do the same for slice except that we need
+		// to use the real index for the bounds checking.
 		if n.Left.Type.IsArray() || (n.Left.Type.IsPtr() && n.Left.Left.Type.IsArray()) {
 			if Isconst(n.Right, CTINT) {
 				// Compute &a.

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

@@ -313,7 +313,7 @@ func transformclosure(xfunc *Node) {
 			} else {
 				// If v of type T is captured by reference,
 				// we introduce function param &v *T
-				// and v remains PPARAMREF with &v heapaddr
+				// and v remains PAUTOHEAP with &v heapaddr
 				// (accesses will implicitly deref &v).
 				addr := newname(Lookupf("&%s", v.Sym.Name))
 				addr.Type = Ptrto(v.Type)

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

@@ -405,7 +405,6 @@ func Complexgen(n *Node, res *Node) {
 		ODOTPTR,
 		OINDEX,
 		OIND,
-		ONAME, // PPARAMREF var
 		OCALLFUNC,
 		OCALLMETH,
 		OCALLINTER:

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

@@ -396,7 +396,8 @@ func oldname(s *Sym) *Node {
 			c := Nod(ONAME, nil, nil)
 
 			c.Sym = s
-			c.Class = PPARAMREF
+			c.Class = PAUTOHEAP
+			c.setIsClosureParam(true)
 			c.Isddd = n.Isddd
 			c.Name.Defn = n
 			c.Addable = false

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

@@ -1817,9 +1817,9 @@ func escwalkBody(e *EscState, level Level, dst *Node, src *Node, step *EscStep,
 			}
 		}
 
-		// Treat a PPARAMREF closure variable as equivalent to the
+		// Treat a captured closure variable as equivalent to the
 		// original variable.
-		if src.Class == PPARAMREF {
+		if src.isClosureParam() {
 			if leaks && Debug['m'] != 0 {
 				Warnl(src.Lineno, "leaking closure reference %v", Nconv(src, FmtShort))
 				step.describe(src)

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

@@ -221,7 +221,6 @@ var classnames = []string{
 	"PAUTOHEAP",
 	"PPARAM",
 	"PPARAMOUT",
-	"PPARAMREF",
 	"PFUNC",
 }
 

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

@@ -43,9 +43,8 @@ func addrescapes(n *Node) {
 			break
 		}
 
-		// A PPARAMREF is a closure reference.
-		// Mark the thing it refers to as escaping.
-		if n.Class == PPARAMREF {
+		// If a closure reference escapes, mark the outer variable as escaping.
+		if n.isClosureParam() {
 			addrescapes(n.Name.Defn)
 			break
 		}
@@ -347,7 +346,7 @@ func cgen_discard(nr *Node) {
 
 	switch nr.Op {
 	case ONAME:
-		if nr.Class != PAUTOHEAP && nr.Class != PEXTERN && nr.Class != PFUNC && nr.Class != PPARAMREF {
+		if nr.Class != PAUTOHEAP && nr.Class != PEXTERN && nr.Class != PFUNC {
 			gused(nr)
 		}
 

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

@@ -94,7 +94,6 @@ const (
 	PAUTOHEAP       // local variable or parameter moved to heap
 	PPARAM          // input arguments
 	PPARAMOUT       // output results
-	PPARAMREF       // closure variable reference
 	PFUNC           // global function
 
 	PDISCARD // discard during parse of duplicate import

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

@@ -495,7 +495,7 @@ func callinstr(np **Node, init *Nodes, wr int, skip int) bool {
 	// e.g. if we've got a local variable/method receiver
 	// 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 == PPARAMREF || class == PEXTERN || b.Op == OINDEX || b.Op == ODOTPTR || b.Op == OIND {
+	if class == PAUTOHEAP || class == PEXTERN || b.Op == OINDEX || b.Op == ODOTPTR || b.Op == OIND {
 		hascalls := 0
 		foreach(n, hascallspred, &hascalls)
 		if hascalls != 0 {

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

@@ -516,7 +516,7 @@ func isliteral(n *Node) bool {
 }
 
 func (n *Node) isSimpleName() bool {
-	return n.Op == ONAME && n.Addable && n.Class != PAUTOHEAP && n.Class != PPARAMREF
+	return n.Op == ONAME && n.Addable && n.Class != PAUTOHEAP
 }
 
 func litas(l *Node, r *Node, init *Nodes) {

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

@@ -2723,8 +2723,6 @@ func (s *state) addr(n *Node, bounded bool) *ssa.Value {
 			// that cse works on their addresses
 			aux := s.lookupSymbol(n, &ssa.ArgSymbol{Typ: n.Type, Node: n})
 			return s.newValue1A(ssa.OpAddr, t, aux, s.sp)
-		case PPARAMREF:
-			return s.expr(n.Name.Heapaddr)
 		default:
 			s.Unimplementedf("variable address class %v not implemented", classnames[n.Class])
 			return nil
@@ -2803,8 +2801,7 @@ func (s *state) canSSA(n *Node) bool {
 		Fatalf("canSSA of PAUTOHEAP %v", n)
 	}
 	switch n.Class {
-	case PEXTERN, PPARAMREF:
-		// TODO: maybe treat PPARAMREF with an Arg-like op to read from closure?
+	case PEXTERN:
 		return false
 	case PPARAMOUT:
 		if hasdefer {

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

@@ -1231,7 +1231,7 @@ func ullmancalc(n *Node) {
 	switch n.Op {
 	case OREGISTER, OLITERAL, ONAME:
 		ul = 1
-		if n.Class == PPARAMREF || n.Class == PAUTOHEAP {
+		if n.Class == PAUTOHEAP {
 			ul++
 		}
 		goto out

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

@@ -78,6 +78,7 @@ type Node struct {
 const (
 	hasBreak = 1 << iota
 	notLiveAtEnd
+	isClosureParam
 )
 
 func (n *Node) HasBreak() bool {
@@ -100,6 +101,16 @@ func (n *Node) SetNotLiveAtEnd(b bool) {
 		n.flags &^= notLiveAtEnd
 	}
 }
+func (n *Node) isClosureParam() bool {
+	return n.flags&isClosureParam != 0
+}
+func (n *Node) setIsClosureParam(b bool) {
+	if b {
+		n.flags |= isClosureParam
+	} else {
+		n.flags &^= isClosureParam
+	}
+}
 
 // Val returns the Val for the node.
 func (n *Node) Val() Val {
@@ -174,9 +185,9 @@ type Param struct {
 	// ONAME PPARAM
 	Field *Field // TFIELD in arg struct
 
-	// ONAME closure param with PPARAMREF
-	Outer   *Node // outer PPARAMREF in nested closure
-	Closure *Node // ONAME/PAUTOHEAP <-> ONAME/PPARAMREF
+	// ONAME closure linkage
+	Outer   *Node
+	Closure *Node
 }
 
 // Func holds Node fields used only with function-like nodes.

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

@@ -647,9 +647,7 @@ opswitch:
 		n.Addable = true
 
 	case ONAME:
-		if n.Class != PPARAMREF {
-			n.Addable = true
-		}
+		n.Addable = true
 
 	case OCALLINTER:
 		usemethod(n)
@@ -2536,7 +2534,7 @@ func vmatch1(l *Node, r *Node) bool {
 	switch l.Op {
 	case ONAME:
 		switch l.Class {
-		case PPARAM, PPARAMREF, PAUTO:
+		case PPARAM, PAUTO:
 			break
 
 			// assignment to non-stack variable

src/cmd/compile/internal/x86/gsubr.go

@@ -724,17 +724,8 @@ func split64(n *gc.Node, lo *gc.Node, hi *gc.Node) {
 
 			n = &n1
 
-		case gc.ONAME:
-			if n.Class == gc.PPARAMREF {
-				var n1 gc.Node
-				gc.Cgen(n.Name.Heapaddr, &n1)
-				sclean[nsclean-1] = n1
-				n = &n1
-			}
-
+		case gc.ONAME, gc.OINDREG:
 			// nothing
-		case gc.OINDREG:
-			break
 		}
 
 		*lo = *n