[dev.regabi] cmd/compile: store types.Field on {Selector,CallPart}Expr

It's useful to have quick access to the types.Field that a given
selector or method value expression refer to. Previously we abused Opt
for this, but couldn't do that for OCALLPART because escape analysis
uses Opt.

Now that we have more flexibility, we can simply add additional
pointer fields for this. This also allows getting rid of an unneeded
ONAME node for OCALLPART.

Passes buildall w/ toolstash -cmp.

Change-Id: I980d7bdb19abfd0b6f58a232876861b88dee1e47
Reviewed-on: https://go-review.googlesource.com/c/go/+/275034
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

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

@@ -427,7 +427,7 @@ func typecheckpartialcall(dot ir.Node, sym *types.Sym) *ir.CallPartExpr {
 	fn := makepartialcall(dot, dot.Type(), sym)
 	fn.SetWrapper(true)
 
-	return ir.NewCallPartExpr(dot.Pos(), dot.Left(), NewName(sym), fn)
+	return ir.NewCallPartExpr(dot.Pos(), dot.Left(), dot.(*ir.SelectorExpr).Selection, fn)
 }
 
 // makepartialcall returns a DCLFUNC node representing the wrapper function (*-fm) needed
@@ -565,16 +565,5 @@ func walkpartialcall(n *ir.CallPartExpr, init *ir.Nodes) ir.Node {
 // callpartMethod returns the *types.Field representing the method
 // referenced by method value n.
 func callpartMethod(n ir.Node) *types.Field {
-	if n.Op() != ir.OCALLPART {
-		base.Fatalf("expected OCALLPART, got %v", n)
-	}
-
-	// TODO(mdempsky): Optimize this. If necessary,
-	// makepartialcall could save m for us somewhere.
-	var m *types.Field
-	if lookdot0(n.Right().Sym(), n.Left().Type(), &m, false) != 1 {
-		base.Fatalf("failed to find field for OCALLPART")
-	}
-
-	return m
+	return n.(*ir.CallPartExpr).Method
 }

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

@@ -1290,8 +1290,7 @@ func (w *exportWriter) expr(n ir.Node) {
 		w.op(ir.OXDOT)
 		w.pos(n.Pos())
 		w.expr(n.Left())
-		// Right node should be ONAME
-		w.selector(n.Right().Sym())
+		w.selector(n.Sym())
 
 	case ir.OXDOT, ir.ODOT, ir.ODOTPTR, ir.ODOTINTER, ir.ODOTMETH:
 		w.op(ir.OXDOT)

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

@@ -430,6 +430,9 @@ func (v *hairyVisitor) visit(n ir.Node) bool {
 		// In any event, let the visitList(n.List()) below take care of the statements,
 		// and don't charge for the OBLOCK itself. The ++ undoes the -- below.
 		v.budget++
+
+	case ir.OCALLPART:
+		v.budget-- // Hack for toolstash -cmp.
 	}
 
 	v.budget--

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

@@ -2385,7 +2385,7 @@ func typecheckMethodExpr(n ir.Node) (res ir.Node) {
 	me.SetType(methodfunc(m.Type, n.Left().Type()))
 	me.SetOffset(0)
 	me.SetClass(ir.PFUNC)
-	me.SetOpt(m)
+	me.(*ir.MethodExpr).Method = m
 
 	// Issue 25065. Make sure that we emit the symbol for a local method.
 	if base.Ctxt.Flag_dynlink && !inimport && (t.Sym() == nil || t.Sym().Pkg == ir.LocalPkg) {
@@ -2448,10 +2448,8 @@ func lookdot(n ir.Node, t *types.Type, dostrcmp int) *types.Field {
 			}
 
 			n.SetOp(ir.ODOTINTER)
-		} else {
-			n.SetOpt(f1)
 		}
-
+		n.(*ir.SelectorExpr).Selection = f1
 		return f1
 	}
 
@@ -2507,7 +2505,7 @@ func lookdot(n ir.Node, t *types.Type, dostrcmp int) *types.Field {
 		n.SetOffset(f2.Offset)
 		n.SetType(f2.Type)
 		n.SetOp(ir.ODOTMETH)
-		n.SetOpt(f2)
+		n.(*ir.SelectorExpr).Selection = f2
 
 		return f2
 	}
@@ -3933,8 +3931,10 @@ func methodExprName(n ir.Node) *ir.Name {
 // MethodFunc is like MethodName, but returns the types.Field instead.
 func methodExprFunc(n ir.Node) *types.Field {
 	switch n.Op() {
-	case ir.ODOTMETH, ir.OMETHEXPR:
-		return n.Opt().(*types.Field)
+	case ir.ODOTMETH:
+		return n.(*ir.SelectorExpr).Selection
+	case ir.OMETHEXPR:
+		return n.(*ir.MethodExpr).Method
 	case ir.OCALLPART:
 		return callpartMethod(n)
 	}

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

@@ -3757,7 +3757,7 @@ func usefield(n ir.Node) {
 	if t.IsPtr() {
 		t = t.Elem()
 	}
-	field := n.Opt().(*types.Field)
+	field := n.(*ir.SelectorExpr).Selection
 	if field == nil {
 		base.Fatalf("usefield %v %v without paramfld", n.Left().Type(), n.Sym())
 	}

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

@@ -205,10 +205,10 @@ type CallPartExpr struct {
 	miniExpr
 	fn     *Func
 	X      Node
-	Method *Name
+	Method *types.Field
 }
 
-func NewCallPartExpr(pos src.XPos, x Node, method *Name, fn *Func) *CallPartExpr {
+func NewCallPartExpr(pos src.XPos, x Node, method *types.Field, fn *Func) *CallPartExpr {
 	n := &CallPartExpr{fn: fn, X: x, Method: method}
 	n.op = OCALLPART
 	n.pos = pos
@@ -222,9 +222,8 @@ func (n *CallPartExpr) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *CallPartExpr) rawCopy() Node                 { c := *n; return &c }
 func (n *CallPartExpr) Func() *Func                   { return n.fn }
 func (n *CallPartExpr) Left() Node                    { return n.X }
-func (n *CallPartExpr) Right() Node                   { return n.Method }
+func (n *CallPartExpr) Sym() *types.Sym               { return n.Method.Sym }
 func (n *CallPartExpr) SetLeft(x Node)                { n.X = x }
-func (n *CallPartExpr) SetRight(x Node)               { n.Method = x.(*Name) }
 
 // A ClosureExpr is a function literal expression.
 type ClosureExpr struct {
@@ -499,6 +498,7 @@ type MethodExpr struct {
 	sym    *types.Sym
 	offset int64
 	class  Class
+	Method *types.Field
 }
 
 func NewMethodExpr(pos src.XPos, op Op, x, m Node) *MethodExpr {
@@ -596,9 +596,10 @@ func (n *ResultExpr) SetOffset(x int64)             { n.offset = x }
 // A SelectorExpr is a selector expression X.Sym.
 type SelectorExpr struct {
 	miniExpr
-	X      Node
-	Sel    *types.Sym
-	offset int64
+	X         Node
+	Sel       *types.Sym
+	offset    int64
+	Selection *types.Field
 }
 
 func NewSelectorExpr(pos src.XPos, x Node, sel *types.Sym) *SelectorExpr {

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

@@ -1382,11 +1382,11 @@ func exprFmt(n Node, s fmt.State, prec int, mode FmtMode) {
 
 	case OCALLPART:
 		exprFmt(n.Left(), s, nprec, mode)
-		if n.Right() == nil || n.Right().Sym() == nil {
+		if n.Sym() == nil {
 			fmt.Fprint(s, ".<nil>")
 			return
 		}
-		mode.Fprintf(s, ".%0S", n.Right().Sym())
+		mode.Fprintf(s, ".%0S", n.Sym())
 
 	case OXDOT, ODOT, ODOTPTR, ODOTINTER, ODOTMETH:
 		exprFmt(n.Left(), s, nprec, mode)