feat(es/minifier): Make minifier parallel (#2009)

swc_ecma_minifier:
 - Introduce `bundle` mode, which can be used to parallelize processing of bundled files.
 - Add a function analyzer that checks if the function references something from the outer scope.
 - Split out parellsizable passes.
 - Split `optimzer` into pure / non-pure.
 - Run pure optimizations in parallel.

Cargo.toml

@@ -70,3 +70,11 @@ lto = true
 [profile.bench]
 codegen-units = 1
 debug = true
+
+# Without this, printing diff consumes more than a minute.
+
+[profile.dev.package.pretty_assertions]
+opt-level = 3
+
+[profile.test.package.pretty_assertions]
+opt-level = 3

ecmascript/minifier/Cargo.toml

@@ -7,7 +7,7 @@ include = ["Cargo.toml", "src/**/*.rs", "src/lists/*.json"]
 license = "Apache-2.0/MIT"
 name = "swc_ecma_minifier"
 repository = "https://github.com/swc-project/swc.git"
-version = "0.18.1"
+version = "0.18.2"
 
 [features]
 debug = []
@@ -18,6 +18,7 @@ indexmap = "1.7.0"
 log = "0.4"
 once_cell = "1.5.2"
 pretty_assertions = {version = "0.6.1", optional = true}
+rayon = "1.5.1"
 regex = "1.5.3"
 retain_mut = "0.1.2"
 serde = {version = "1.0.118", features = ["derive"]}

ecmascript/minifier/src/analyzer/ctx.rs

@@ -16,6 +16,9 @@ impl UsageAnalyzer {
 
 #[derive(Debug, Default, Clone, Copy)]
 pub(super) struct Ctx {
+    /// See [crate::marks::Marks]
+    pub skip_standalone: bool,
+
     pub var_decl_kind_of_pat: Option<VarDeclKind>,
 
     pub in_var_decl_with_no_side_effect_for_member_access: bool,

ecmascript/minifier/src/analyzer/mod.rs

@@ -23,7 +23,9 @@ mod ctx;
 
 /// TODO: Track assignments to variables via `arguments`.
 /// TODO: Scope-local. (Including block)
-pub(crate) fn analyze<N>(n: &N, marks: Marks) -> ProgramData
+///
+/// If `marks` is [None], markers are ignored.
+pub(crate) fn analyze<N>(n: &N, marks: Option<Marks>) -> ProgramData
 where
     N: VisitWith<UsageAnalyzer>,
 {
@@ -237,7 +239,7 @@ impl ProgramData {
 #[derive(Debug)]
 pub(crate) struct UsageAnalyzer {
     data: ProgramData,
-    marks: Marks,
+    marks: Option<Marks>,
     scope: ScopeData,
     ctx: Ctx,
 }
@@ -415,7 +417,11 @@ impl Visit for UsageAnalyzer {
     }
 
     fn visit_call_expr(&mut self, n: &CallExpr, _: &dyn Node) {
-        let inline_prevented = self.ctx.inline_prevented || n.span.has_mark(self.marks.noinline);
+        let inline_prevented = self.ctx.inline_prevented
+            || self
+                .marks
+                .map(|marks| n.span.has_mark(marks.noinline))
+                .unwrap_or_default();
 
         {
             let ctx = Ctx {
@@ -588,18 +594,35 @@ impl Visit for UsageAnalyzer {
     fn visit_function(&mut self, n: &Function, _: &dyn Node) {
         n.decorators.visit_with(n, self);
 
-        self.with_child(n.span.ctxt, ScopeKind::Fn, |child| {
-            n.params.visit_with(n, child);
+        let is_standalone = self
+            .marks
+            .map(|marks| n.span.has_mark(marks.standalone))
+            .unwrap_or_default();
 
-            match &n.body {
-                Some(body) => {
-                    // We use visit_children_with instead of visit_with to bypass block scope
-                    // handler.
-                    body.visit_children_with(child);
+        // We don't dig into standalone function, as it does not share any variable with
+        // outer scope.
+        if self.ctx.skip_standalone && is_standalone {
+            return;
+        }
+
+        let ctx = Ctx {
+            skip_standalone: self.ctx.skip_standalone || is_standalone,
+            ..self.ctx
+        };
+
+        self.with_ctx(ctx)
+            .with_child(n.span.ctxt, ScopeKind::Fn, |child| {
+                n.params.visit_with(n, child);
+
+                match &n.body {
+                    Some(body) => {
+                        // We use visit_children_with instead of visit_with to bypass block scope
+                        // handler.
+                        body.visit_children_with(child);
+                    }
+                    None => {}
                 }
-                None => {}
-            }
-        })
+            })
     }
 
     fn visit_if_stmt(&mut self, n: &IfStmt, _: &dyn Node) {
@@ -665,6 +688,14 @@ impl Visit for UsageAnalyzer {
         }
     }
 
+    fn visit_module(&mut self, n: &Module, _: &dyn Node) {
+        let ctx = Ctx {
+            skip_standalone: true,
+            ..self.ctx
+        };
+        n.visit_children_with(&mut *self.with_ctx(ctx))
+    }
+
     fn visit_named_export(&mut self, n: &NamedExport, _: &dyn Node) {
         if n.src.is_some() {
             return;