diff --git a/vlib/strings/builder.c.v b/vlib/strings/builder.c.v
index 76a5f92d4f..c59718ca84 100644
--- a/vlib/strings/builder.c.v
+++ b/vlib/strings/builder.c.v
@@ -47,6 +47,11 @@ pub fn (b mut Builder) go_back(n int) {
 	b.len -= n
 }
 
+pub fn (b mut Builder) go_back_to(pos int) {
+	b.buf.trim(pos)
+	b.len = pos
+}
+
 pub fn (b mut Builder) writeln(s string) {
 	// for c in s {
 	// b.buf << c
diff --git a/vlib/v/builder/cc.v b/vlib/v/builder/cc.v
index e5a53d8243..c7cffa7430 100644
--- a/vlib/v/builder/cc.v
+++ b/vlib/v/builder/cc.v
@@ -308,7 +308,7 @@ fn (mut v Builder) cc() {
 	if v.pref.use_cache {
 		//vexe := pref.vexe_path()
 
-		cached_modules:= [ 'builtin', 'os' ]//, 'math']
+		cached_modules:= [ 'builtin', 'os', 'math', 'strconv', 'strings']
 		for cfile in cached_modules{
 			ofile := os.join_path(pref.default_module_path, 'cache', 'vlib', cfile + '.o')
 			if !os.exists(ofile) {
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index aebac12d51..5478c1bc37 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -58,6 +58,7 @@ struct Gen {
 	pcs_declarations     strings.Builder // -prof profile counter declarations for each function
 	table                &table.Table
 	pref                 &pref.Preferences
+	module_built         string
 mut:
 	file                 ast.File
 	fn_decl              &ast.FnDecl // pointer to the FnDecl we are currently inside otherwise 0
@@ -86,6 +87,8 @@ mut:
 	array_fn_definitions []string // array equality functions that have been defined
 	is_json_fn           bool // inside json.encode()
 	pcs                  []ProfileCounterMeta // -prof profile counter fn_names => fn counter name
+	attr string
+	is_builtin_mod bool
 }
 
 const (
@@ -122,6 +125,7 @@ pub fn cgen(files []ast.File, table &table.Table, pref &pref.Preferences) string
 		fn_decl: 0
 		autofree: true
 		indent: -1
+		module_built: pref.path.after('vlib/')
 	}
 	g.init()
 	//
@@ -159,7 +163,6 @@ pub fn cgen(files []ast.File, table &table.Table, pref &pref.Preferences) string
 	//
 	g.finish()
 	//
-
 	b := strings.new_builder(250000)
 	b.writeln(g.hashes())
 	b.writeln(g.comptime_defines.str())
@@ -238,7 +241,6 @@ pub fn (mut g Gen) finish() {
 	}
 	g.stringliterals.writeln('// << string literal consts')
 	g.stringliterals.writeln('')
-
 	if g.pref.is_prof {
 		g.gen_vprint_profile_stats()
 	}
@@ -446,8 +448,9 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			g.gen_assign_stmt(it)
 		}
 		ast.Attr {
+			g.attr = it.name
 			if it.name == 'inline' {
-				g.writeln(it.name)
+				//g.writeln(it.name)
 			} else {
 				g.writeln('//[$it.name]')
 			}
@@ -512,12 +515,30 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			}
 		}
 		ast.FnDecl {
+			mut skip := false
+			pos := g.out.buf.len
+			if g.pref.build_mode==.build_module {
+				if !it.name.starts_with(g.module_built + '.'){
+					// Skip functions that don't have to be generated
+					// for this module.
+					skip =  true
+				}
+				if g.is_builtin_mod && g.module_built == 'builtin' {
+					skip=false
+				}
+				if !skip {
+					println('build module `$g.module_built` fn `$it.name`')
+				}
+			}
 			fn_start_pos := g.out.len
 			g.fn_decl = it // &it
 			g.gen_fn_decl(it)
 			if g.pref.printfn_list.len > 0 && g.last_fn_c_name in g.pref.printfn_list {
 				println(g.out.after(fn_start_pos))
 			}
+			if skip {
+				g.out.go_back_to(pos)
+			}
 			g.writeln('')
 		}
 		ast.ForCStmt {
@@ -584,7 +605,9 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			g.definitions.writeln('\tint _interface_idx;')
 			g.definitions.writeln('} $it.name;')
 		}
-		ast.Module {}
+		ast.Module {
+			g.is_builtin_mod = it.name=='builtin'
+		}
 		ast.Return {
 			g.write_defer_stmts_when_needed()
 			g.return_statement(it)
diff --git a/vlib/v/gen/fn.v b/vlib/v/gen/fn.v
index e0941ed3ca..163ff5d2bd 100644
--- a/vlib/v/gen/fn.v
+++ b/vlib/v/gen/fn.v
@@ -12,6 +12,10 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl) {
 		// || it.no_body {
 		return
 	}
+	if g.attr == 'inline' {
+		g.write('inline ')
+		g.attr = ''
+	}
 	g.reset_tmp_count()
 	is_main := it.name == 'main'
 	if is_main {