ssa: fix ssa.Index and indexType

ssa/datastruct.go

@@ -163,13 +163,14 @@ func (b Builder) checkIndex(idx Expr) Expr {
 // Example printed form:
 //
 //	t2 = t0[t1]
-func (b Builder) Index(x, idx Expr, addr func(Expr) Expr) Expr {
+func (b Builder) Index(x, idx Expr, addr func(Expr) (Expr, bool)) Expr {
 	if debugInstr {
 		log.Printf("Index %v, %v\n", x.impl, idx.impl)
 	}
 	prog := b.Prog
 	var telem Type
 	var ptr Expr
+	var zero bool
 	switch t := x.raw.Type.Underlying().(type) {
 	case *types.Basic:
 		if t.Kind() != types.String {
@@ -180,7 +181,7 @@ func (b Builder) Index(x, idx Expr, addr func(Expr) Expr) Expr {
 	case *types.Array:
 		telem = prog.Index(x.Type)
 		if addr != nil {
-			ptr = addr(x)
+			ptr, zero = addr(x)
 		} else {
 			/*
 				size := SizeOf(prog, telem, t.Len())
@@ -190,7 +191,11 @@ func (b Builder) Index(x, idx Expr, addr func(Expr) Expr) Expr {
 			panic("unreachable")
 		}
 	}
+	// TODO check range
 	idx = b.checkIndex(idx)
+	if zero {
+		return Expr{llvm.ConstNull(telem.ll), telem}
+	}
 	pt := prog.Pointer(telem)
 	indices := []llvm.Value{idx.impl}
 	buf := Expr{llvm.CreateInBoundsGEP(b.impl, telem.ll, ptr.impl, indices), pt}

ssa/type.go

@@ -61,11 +61,16 @@ const (
 // -----------------------------------------------------------------------------
 
 func indexType(t types.Type) types.Type {
-	switch t := t.(type) {
+	typ := t
+retry:
+	switch t := typ.(type) {
+	case *types.Named:
+		typ = t.Underlying()
+		goto retry
 	case *types.Slice:
 		return t.Elem()
 	case *types.Pointer:
-		switch t := t.Elem().(type) {
+		switch t := t.Elem().Underlying().(type) {
 		case *types.Array:
 			return t.Elem()
 		}
@@ -193,7 +198,7 @@ func (p Program) Pointer(typ Type) Type {
 }
 
 func (p Program) Elem(typ Type) Type {
-	elem := typ.raw.Type.(interface {
+	elem := typ.raw.Type.Underlying().(interface {
 		Elem() types.Type
 	}).Elem()
 	return p.rawType(elem)