checker, cgen: fix call of generic function returning normal type (#5865)

vlib/v/checker/checker.v

@@ -1116,7 +1116,7 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 	if f.is_deprecated {
 		c.warn('function `$f.name` has been deprecated', call_expr.pos)
 	}
-	if f.is_generic {
+	if f.is_generic && f.return_type.has_flag(.generic) {
 		rts := c.table.get_type_symbol(f.return_type)
 		if rts.kind == .struct_ {
 			rts_info := rts.info as table.Struct

vlib/v/gen/cgen.v

@@ -1785,14 +1785,15 @@ fn (mut g Gen) expr(node ast.Expr) {
 		}
 		ast.SizeOf {
 			if node.is_type {
+				node_typ := g.unwrap_generic(node.typ)
 				mut styp := node.type_name
 				if styp.starts_with('C.') {
 					styp = styp[2..]
 				}
-				if node.type_name == '' {
-					styp = g.typ(node.typ)
+				if node.type_name == '' || node.typ.has_flag(.generic) {
+					styp = g.typ(node_typ)
 				} else {
-					sym := g.table.get_type_symbol(node.typ)
+					sym := g.table.get_type_symbol(node_typ)
 					if sym.kind == .struct_ {
 						info := sym.info as table.Struct
 						if !info.is_typedef {

vlib/v/tests/sizeof_2_test.v

@@ -0,0 +1,8 @@
+fn getsize<P>() u32 {
+	return sizeof(P)
+}
+
+fn test_sizeof_2() {
+	assert getsize<f64>() == 8
+	assert 4 == getsize<int>()
+}