cmd/compile: set ir.Name.Func in more cases

ir.Name.Func is non-nil for *almost* all function names. This CL fixes
a few more major cases that leave it nil, though there are still a few
cases left: interface method values, and algorithms generated by
eqFor, hashfor, and hashmem.

We'll need this for mapping from ir.Names to function ABIs shortly.
The remaining cases would be nice to fix, but they're all guaranteed
to be ABIInternal, so we can at least work around them.

For #40724.

Change-Id: Ifcfa781c78899ccea0bf155d80f8cfc27f30351e
Reviewed-on: https://go-review.googlesource.com/c/go/+/305271
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -528,6 +528,13 @@ func (n *SelectorExpr) FuncName() *Name {
 	fn := NewNameAt(n.Selection.Pos, MethodSym(n.X.Type(), n.Sel))
 	fn.Class = PFUNC
 	fn.SetType(n.Type())
+	if n.Selection.Nname != nil {
+		// TODO(austin): Nname is nil for interface method
+		// expressions (I.M), so we can't attach a Func to
+		// those here. reflectdata.methodWrapper generates the
+		// Func.
+		fn.Func = n.Selection.Nname.(*Name).Func
+	}
 	return fn
 }
 

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

@@ -41,7 +41,7 @@ type Name struct {
 	pragma    PragmaFlag // int16
 	flags     bitset16
 	sym       *types.Sym
-	Func      *Func
+	Func      *Func // TODO(austin): nil for I.M, eqFor, hashfor, and hashmem
 	Offset_   int64
 	val       constant.Value
 	Opt       interface{} // for use by escape analysis

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

@@ -287,6 +287,7 @@ func hashfor(t *types.Type) ir.Node {
 		sym = TypeSymPrefix(".hash", t)
 	}
 
+	// TODO(austin): This creates an ir.Name with a nil Func.
 	n := typecheck.NewName(sym)
 	ir.MarkFunc(n)
 	n.SetType(types.NewSignature(types.NoPkg, nil, nil, []*types.Field{
@@ -775,6 +776,7 @@ func memrun(t *types.Type, start int) (size int64, next int) {
 func hashmem(t *types.Type) ir.Node {
 	sym := ir.Pkgs.Runtime.Lookup("memhash")
 
+	// TODO(austin): This creates an ir.Name with a nil Func.
 	n := typecheck.NewName(sym)
 	ir.MarkFunc(n)
 	n.SetType(types.NewSignature(types.NoPkg, nil, nil, []*types.Field{

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

@@ -1741,6 +1741,9 @@ func methodWrapper(rcvr *types.Type, method *types.Field) *obj.LSym {
 		typecheck.NewFuncParams(method.Type.Params(), true),
 		typecheck.NewFuncParams(method.Type.Results(), false))
 
+	// TODO(austin): SelectorExpr may have created one or more
+	// ir.Names for these already with a nil Func field. We should
+	// consolidate these and always attach a Func to the Name.
 	fn := typecheck.DeclFunc(newnam, tfn)
 	fn.SetDupok(true)
 

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

@@ -32,6 +32,7 @@ func SubstArgTypes(old *ir.Name, types_ ...*types.Type) *ir.Name {
 	n := ir.NewNameAt(old.Pos(), old.Sym())
 	n.Class = old.Class
 	n.SetType(types.SubstAny(old.Type(), &types_))
+	n.Func = old.Func
 	if len(types_) > 0 {
 		base.Fatalf("SubstArgTypes: too many argument types")
 	}

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

@@ -426,6 +426,7 @@ func eqFor(t *types.Type) (n ir.Node, needsize bool) {
 		return n, true
 	case types.ASPECIAL:
 		sym := reflectdata.TypeSymPrefix(".eq", t)
+		// TODO(austin): This creates an ir.Name with a nil Func.
 		n := typecheck.NewName(sym)
 		ir.MarkFunc(n)
 		n.SetType(types.NewSignature(types.NoPkg, nil, nil, []*types.Field{