[dev.regabi] cmd/compile: remove SelectorExpr.Offset field

Now that the previous CL ensures we always set SelectorExpr.Selection,
we can replace the SelectorExpr.Offset field with a helper method that
simply returns SelectorExpr.Selection.Offset.

Passes toolstash -cmp.

Change-Id: Id0f22b8b1980397b668f6860d27cb197b90ff52a
Reviewed-on: https://go-review.googlesource.com/c/go/+/280433
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/ir/expr.go

@@ -572,14 +572,12 @@ type SelectorExpr struct {
 	miniExpr
 	X         Node
 	Sel       *types.Sym
-	Offset    int64
 	Selection *types.Field
 }
 
 func NewSelectorExpr(pos src.XPos, op Op, x Node, sel *types.Sym) *SelectorExpr {
 	n := &SelectorExpr{X: x, Sel: sel}
 	n.pos = pos
-	n.Offset = types.BADWIDTH
 	n.SetOp(op)
 	return n
 }
@@ -596,6 +594,7 @@ func (n *SelectorExpr) SetOp(op Op) {
 func (n *SelectorExpr) Sym() *types.Sym    { return n.Sel }
 func (n *SelectorExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
 func (n *SelectorExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
+func (n *SelectorExpr) Offset() int64      { return n.Selection.Offset }
 
 // Before type-checking, bytes.Buffer is a SelectorExpr.
 // After type-checking it becomes a Name.

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1863,7 +1863,7 @@ func MarkUsedIfaceMethod(n *ir.CallExpr) {
 	r.Sym = tsym
 	// dot.Xoffset is the method index * Widthptr (the offset of code pointer
 	// in itab).
-	midx := dot.Offset / int64(types.PtrSize)
+	midx := dot.Offset() / int64(types.PtrSize)
 	r.Add = InterfaceMethodOffset(ityp, midx)
 	r.Type = objabi.R_USEIFACEMETHOD
 }

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

@@ -2743,7 +2743,7 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 	case ir.ODOTPTR:
 		n := n.(*ir.SelectorExpr)
 		p := s.exprPtr(n.X, n.Bounded(), n.Pos())
-		p = s.newValue1I(ssa.OpOffPtr, types.NewPtr(n.Type()), n.Offset, p)
+		p = s.newValue1I(ssa.OpOffPtr, types.NewPtr(n.Type()), n.Offset(), p)
 		return s.load(n.Type(), p)
 
 	case ir.OINDEX:
@@ -4924,7 +4924,7 @@ func (s *state) getClosureAndRcvr(fn *ir.SelectorExpr) (*ssa.Value, *ssa.Value)
 	i := s.expr(fn.X)
 	itab := s.newValue1(ssa.OpITab, types.Types[types.TUINTPTR], i)
 	s.nilCheck(itab)
-	itabidx := fn.Offset + 2*int64(types.PtrSize) + 8 // offset of fun field in runtime.itab
+	itabidx := fn.Offset() + 2*int64(types.PtrSize) + 8 // offset of fun field in runtime.itab
 	closure := s.newValue1I(ssa.OpOffPtr, s.f.Config.Types.UintptrPtr, itabidx, itab)
 	rcvr := s.newValue1(ssa.OpIData, s.f.Config.Types.BytePtr, i)
 	return closure, rcvr
@@ -5028,11 +5028,11 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 	case ir.ODOT:
 		n := n.(*ir.SelectorExpr)
 		p := s.addr(n.X)
-		return s.newValue1I(ssa.OpOffPtr, t, n.Offset, p)
+		return s.newValue1I(ssa.OpOffPtr, t, n.Offset(), p)
 	case ir.ODOTPTR:
 		n := n.(*ir.SelectorExpr)
 		p := s.exprPtr(n.X, n.Bounded(), n.Pos())
-		return s.newValue1I(ssa.OpOffPtr, t, n.Offset, p)
+		return s.newValue1I(ssa.OpOffPtr, t, n.Offset(), p)
 	case ir.OCLOSUREREAD:
 		n := n.(*ir.ClosureReadExpr)
 		return s.newValue1I(ssa.OpOffPtr, t, n.Offset,
@@ -7069,22 +7069,18 @@ func (s *State) UseArgs(n int64) {
 // fieldIdx finds the index of the field referred to by the ODOT node n.
 func fieldIdx(n *ir.SelectorExpr) int {
 	t := n.X.Type()
-	f := n.Sel
 	if !t.IsStruct() {
 		panic("ODOT's LHS is not a struct")
 	}
 
-	var i int
+	for i, f := range t.Fields().Slice() {
-	for _, t1 := range t.Fields().Slice() {
+		if f.Sym == n.Sel {
-		if t1.Sym != f {
+			if f.Offset != n.Offset() {
-			i++
-			continue
-		}
-		if t1.Offset != n.Offset {
 				panic("field offset doesn't match")
 			}
 			return i
 		}
+	}
 	panic(fmt.Sprintf("can't find field in expr %v\n", n))
 
 	// TODO: keep the result of this function somewhere in the ODOT Node

src/cmd/compile/internal/staticinit/sched.go

@@ -469,7 +469,7 @@ func StaticLoc(n ir.Node) (name *ir.Name, offset int64, ok bool) {
 		if name, offset, ok = StaticLoc(n.X); !ok {
 			break
 		}
-		offset += n.Offset
+		offset += n.Offset()
 		return name, offset, true
 
 	case ir.OINDEX:

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

@@ -929,7 +929,7 @@ func evalunsafe(n ir.Node) int64 {
 				fallthrough
 			case ir.ODOT:
 				r := r.(*ir.SelectorExpr)
-				v += r.Offset
+				v += r.Offset()
 				next = r.X
 			default:
 				ir.Dump("unsafenmagic", tsel)

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

@@ -1232,7 +1232,7 @@ func lookdot(n *ir.SelectorExpr, t *types.Type, dostrcmp int) *types.Field {
 		if f1.Offset == types.BADWIDTH {
 			base.Fatalf("lookdot badwidth %v %p", f1, f1)
 		}
-		n.Offset = f1.Offset
+		n.Selection = f1
 		n.SetType(f1.Type)
 		if t.IsInterface() {
 			if n.X.Type().IsPtr() {
@@ -1243,7 +1243,6 @@ func lookdot(n *ir.SelectorExpr, t *types.Type, dostrcmp int) *types.Field {
 
 			n.SetOp(ir.ODOTINTER)
 		}
-		n.Selection = f1
 		return f1
 	}
 
@@ -1299,10 +1298,9 @@ func lookdot(n *ir.SelectorExpr, t *types.Type, dostrcmp int) *types.Field {
 		}
 
 		n.Sel = ir.MethodSym(n.X.Type(), f2.Sym)
-		n.Offset = f2.Offset
+		n.Selection = f2
 		n.SetType(f2.Type)
 		n.SetOp(ir.ODOTMETH)
-		n.Selection = f2
 
 		return f2
 	}

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

@@ -965,22 +965,13 @@ func usefield(n *ir.SelectorExpr) {
 	case ir.ODOT, ir.ODOTPTR:
 		break
 	}
-	if n.Sel == nil {
-		// No field name.  This DOTPTR was built by the compiler for access
-		// to runtime data structures.  Ignore.
-		return
-	}
 
-	t := n.X.Type()
-	if t.IsPtr() {
-		t = t.Elem()
-	}
 	field := n.Selection
 	if field == nil {
 		base.Fatalf("usefield %v %v without paramfld", n.X.Type(), n.Sel)
 	}
-	if field.Sym != n.Sel || field.Offset != n.Offset {
+	if field.Sym != n.Sel {
-		base.Fatalf("field inconsistency: %v,%v != %v,%v", field.Sym, field.Offset, n.Sel, n.Offset)
+		base.Fatalf("field inconsistency: %v != %v", field.Sym, n.Sel)
 	}
 	if !strings.Contains(field.Note, "go:\"track\"") {
 		return

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

@@ -553,7 +553,6 @@ var itabTypeField *types.Field
 func boundedDotPtr(pos src.XPos, ptr ir.Node, field *types.Field) *ir.SelectorExpr {
 	sel := ir.NewSelectorExpr(pos, ir.ODOTPTR, ptr, field.Sym)
 	sel.Selection = field
-	sel.Offset = field.Offset
 	sel.SetType(field.Type)
 	sel.SetTypecheck(1)
 	sel.SetBounded(true) // guaranteed not to fault