cmd/compile: generate type equal func during walk

So we don't generate ONAME node with nil Func.

Do not pass toolstash-check because the CL changes the order of
compiling functions.

Change-Id: Ib967328f36b8c59a5525445667103c0c80ccdc82
Reviewed-on: https://go-review.googlesource.com/c/go/+/436436
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -357,16 +357,19 @@ func geneq(t *types.Type) *obj.LSym {
 
 func eqFunc(t *types.Type) *ir.Func {
 	// Autogenerate code for equality of structs and arrays.
-
+	sym := TypeSymPrefix(".eq", t)
+	if sym.Def != nil {
+		return sym.Def.(*ir.Name).Func
+	}
 	base.Pos = base.AutogeneratedPos // less confusing than end of input
 	typecheck.DeclContext = ir.PEXTERN
 
 	// func sym(p, q *T) bool
-	sym := TypeSymPrefix(".eq", t)
 	fn := typecheck.DeclFunc(sym, nil,
 		[]*ir.Field{ir.NewField(base.Pos, typecheck.Lookup("p"), types.NewPtr(t)), ir.NewField(base.Pos, typecheck.Lookup("q"), types.NewPtr(t))},
 		[]*ir.Field{ir.NewField(base.Pos, typecheck.Lookup("r"), types.Types[types.TBOOL])},
 	)
+	sym.Def = fn.Nname
 	np := ir.AsNode(fn.Type().Params().Field(0).Nname)
 	nq := ir.AsNode(fn.Type().Params().Field(1).Nname)
 	nr := ir.AsNode(fn.Type().Results().Field(0).Nname)
@@ -554,9 +557,9 @@ func eqFunc(t *types.Type) *ir.Func {
 	fn.SetDupok(true)
 	typecheck.Func(fn)
 
-	ir.CurFunc = fn
+	ir.WithFunc(fn, func() {
-	typecheck.Stmts(fn.Body)
+		typecheck.Stmts(fn.Body)
-	ir.CurFunc = nil
+	})
 
 	// Disable checknils while compiling this code.
 	// We are comparing a struct or an array,
@@ -567,6 +570,22 @@ func eqFunc(t *types.Type) *ir.Func {
 	return fn
 }
 
+// EqFor returns ONAME node represents type t's equal function, and a boolean
+// to indicates whether a length needs to be passed when calling the function.
+func EqFor(t *types.Type) (ir.Node, bool) {
+	switch a, _ := types.AlgType(t); a {
+	case types.AMEM:
+		n := typecheck.LookupRuntime("memequal")
+		n = typecheck.SubstArgTypes(n, t, t)
+		return n, true
+	case types.ASPECIAL:
+		fn := eqFunc(t)
+		return fn.Nname, false
+	}
+	base.Fatalf("EqFor %v", t)
+	return nil, false
+}
+
 func anyCall(fn *ir.Func) bool {
 	return ir.Any(fn, func(n ir.Node) bool {
 		// TODO(rsc): No methods?

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

@@ -186,11 +186,15 @@ func walkCompare(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 			base.Fatalf("arguments of comparison must be lvalues - %v %v", cmpl, cmpr)
 		}
 
-		fn, needsize := eqFor(t)
+		// Should only arrive here with large memory or
+		// a struct/array containing a non-memory field/element.
+		// Small memory is handled inline, and single non-memory
+		// is handled by walkCompare.
+		fn, needsLength := reflectdata.EqFor(t)
 		call := ir.NewCallExpr(base.Pos, ir.OCALL, fn, nil)
 		call.Args.Append(typecheck.NodAddr(cmpl))
 		call.Args.Append(typecheck.NodAddr(cmpr))
-		if needsize {
+		if needsLength {
 			call.Args.Append(ir.NewInt(t.Size()))
 		}
 		res := ir.Node(call)