v.pref: support `v -skip-unused run examples/hello_world.v`

vlib/v/checker/checker.v

@@ -12,8 +12,6 @@ import v.pref
 import v.util
 import v.errors
 import v.pkgconfig
-import v.walker
-import time
 
 const (
 	max_nr_errors                 = 300
@@ -229,26 +227,8 @@ pub fn (mut c Checker) check_files(ast_files []ast.File) {
 	} else if !has_main_fn {
 		c.error('function `main` must be declared in the main module', token.Position{})
 	}
-	// Walk the tree starting at main() and mark all used fns.
-	if c.pref.experimental {
-		println('walking the ast')
-		// c.is_recursive = true
-		// c.fn_decl(mut c.table2.main_fn_decl_node)
-		t := time.ticks()
-		mut walker := walker.Walker{
-			files: ast_files
-		}
-		for stmt in c.main_fn_decl_node.stmts {
-			walker.stmt(stmt)
-		}
-		// walker.fn_decl(mut c.table2.main_fn_decl_node)
-		println('time = ${time.ticks() - t}ms, nr used fns=$walker.used_fns.len')
-
-		for key, _ in walker.used_fns {
-			println(key)
-		}
-		// println(walker.used_fns)
-		// c.walk(ast_files)
+	if c.pref.skip_unused {
+		c.mark_used(ast_files)
 	}
 }
 

vlib/v/checker/mark_used.v

@@ -0,0 +1,92 @@
+module checker
+
+import v.ast
+import v.table
+import v.checker.mark_used_walker
+
+// mark_used walks the AST, starting at main() and marks all used fns transitively
+fn (mut c Checker) mark_used(ast_files []ast.File) {
+	// println('walking the ast')
+	// c.is_recursive = true
+	// c.fn_decl(mut c.table2.main_fn_decl_node)
+
+	// c.timing_measure(@FN)
+	mut walker := mark_used_walker.Walker{
+		files: ast_files
+	}
+
+	// TODO: walking over the AST using roots != main.main, like `panic`
+	// for example, will potentially eliminate many cases where manual
+	// whitelisting is needed.
+	// TODO: use the full name of the functions in the map. For now the
+	// receiver type is skipped, so we can not distinguish between
+	// array.trim and string.trim etc.
+	for stmt in c.main_fn_decl_node.stmts {
+		walker.stmt(stmt)
+	}
+	// walker.fn_decl(mut c.table2.main_fn_decl_node)
+	// println('time = ${time.ticks() - t}ms, nr used fns=$walker.used_fns.len')
+
+	/*
+	for key, _ in walker.used_fns {
+		println(key)
+	}
+	*/
+	c.table.used_fns = walker.used_fns
+
+	// Whitelist some functions that are used by cgen directly:
+	c.table.used_fns['tos'] = true
+	c.table.used_fns['tos2'] = true
+	c.table.used_fns['v_panic'] = true
+	c.table.used_fns['panic'] = true
+	c.table.used_fns['eprintln'] = true
+	c.table.used_fns['print_backtrace_skipping_top_frames'] = true
+	c.table.used_fns['print_backtrace_skipping_top_frames_linux'] = true
+	c.table.used_fns['new_array_from_c_array'] = true
+	c.table.used_fns['__new_array_with_default'] = true
+	c.table.used_fns['__new_array'] = true
+	c.table.used_fns['vcalloc'] = true
+	c.table.used_fns['set_unsafe'] = true
+	c.table.used_fns['get_unsafe'] = true
+	c.table.used_fns['push'] = true
+	c.table.used_fns['ensure_cap'] = true
+	c.table.used_fns['v_realloc'] = true
+	c.table.used_fns['all_before'] = true
+	c.table.used_fns['all_after'] = true
+	c.table.used_fns['add'] = true
+	c.table.used_fns['isnil'] = true
+	c.table.used_fns['vstrlen'] = true
+	c.table.used_fns['trim_space'] = true
+	c.table.used_fns['malloc'] = true
+	c.table.used_fns['trim'] = true
+	c.table.used_fns['at'] = true
+	c.table.used_fns['replace'] = true
+	c.table.used_fns['index_'] = true
+	c.table.used_fns['index_after'] = true
+	c.table.used_fns['index_kmp'] = true
+	c.table.used_fns['substr'] = true
+	c.table.used_fns['clone'] = true
+	c.table.used_fns['free'] = true
+	c.table.used_fns['has_index'] = true
+	c.table.used_fns['key'] = true
+	c.table.used_fns['set'] = true
+	c.table.used_fns['get'] = true
+	c.table.used_fns['new_node'] = true
+	c.table.used_fns['eq'] = true
+	c.table.used_fns['ne'] = true
+	c.table.used_fns['lt'] = true
+	c.table.used_fns['gt'] = true
+	c.table.used_fns['le'] = true
+	c.table.used_fns['ge'] = true
+	c.table.used_fns['split_child'] = true
+	c.table.used_fns['bytes'] = true
+	c.table.used_fns['utf8_char_len'] = true
+	c.table.used_fns['utf8_str_visible_length'] = true
+	c.table.used_fns['main.main'] = true
+	c.table.used_fns['builtin_init'] = true
+	c.table.used_fns['memdup'] = true
+	// c.timing_measure(@FN)
+
+	// println(walker.used_fns)
+	// c.walk(ast_files)
+}

vlib/v/checker/mark_used_walker/walker.v

@@ -1,9 +1,8 @@
 // Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
 // Use of this source code is governed by an MIT license that can be found in the LICENSE file.
-module walker
+module mark_used_walker
 
-// This module walks the entire program starting at fn main and marks used (called)
-// functions.
+// This module walks the entire program starting at fn main and marks used (called) functions.
 // Unused functions can be safely skipped by the backends to save CPU time and space.
 import v.ast
 
@@ -91,7 +90,7 @@ pub fn (mut w Walker) fn_decl(mut node ast.FnDecl) {
 	if node.language == .c {
 		return
 	}
-	println('fn decl $fn_name')
+	// println('fn decl $fn_name')
 	w.used_fns[fn_name] = true
 	for stmt in node.stmts {
 		w.stmt(stmt)
@@ -102,7 +101,7 @@ pub fn (mut w Walker) fn_decl(mut node ast.FnDecl) {
 pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 	fn_name := if node.is_method { node.receiver_type.str() + '.' + node.name } else { node.name }
 	// fn_name := node.name
-	println('call_expr $fn_name')
+	// println('call_expr $fn_name')
 	// if node.is_method {
 	// println('M $node.name $node.receiver_type')
 	//}

vlib/v/gen/c/fn.v

@@ -27,13 +27,12 @@ fn (mut g Gen) gen_fn_decl(node ast.FnDecl, skip bool) {
 		}
 	}
 	*/
-	if g.pref.experimental {
-		if f := g.table.find_fn(node.name) {
-			println('> usages: ${f.usages:-10} | node.name: $node.name')
-			if f.usages == 0 {
-				g.writeln('// fn $node.name UNUSED')
-				return
-			}
+	if g.pref.skip_unused {
+		is_used_by_main := g.table.used_fns[ node.name ]
+		// println('> is_used_by_main: $is_used_by_main | node.name: $node.name')
+		if !is_used_by_main {
+			g.writeln('// fn $node.name UNUSED')
+			return
 		}
 	}
 

vlib/v/pref/pref.v

@@ -136,6 +136,7 @@ pub mut:
 	is_vweb             bool // skip _ var warning in templates
 	only_check_syntax   bool // when true, just parse the files, then stop, before running checker
 	experimental        bool // enable experimental features
+	skip_unused         bool // skip generating C code for functions, that are not used
 	show_timings        bool // show how much time each compiler stage took
 	is_ios_simulator    bool
 	is_apk              bool     // build as Android .apk format
@@ -221,6 +222,9 @@ pub fn parse_args(args []string) (&Preferences, string) {
 				res.autofree = false
 				res.build_options << arg
 			}
+			'-skip-unused' {
+				res.skip_unused = true
+			}
 			'-compress' {
 				res.compress = true
 			}

vlib/v/table/table.v

@@ -19,6 +19,7 @@ pub mut:
 	fn_gen_types  map[string][][]Type // for generic functions
 	cmod_prefix   string // needed for table.type_to_str(Type) while vfmt; contains `os.`
 	is_fmt        bool
+	used_fns      map[string]bool // filled in by the checker, when pref.skip_unused = true;
 }
 
 pub struct Fn {