swc_ecma_minifier/compress/

hoist_decls.rs

use par_iter::prelude::*;
use rustc_hash::FxHashSet;
use swc_common::{pass::Repeated, util::take::Take, DUMMY_SP};
use swc_ecma_ast::*;
use swc_ecma_usage_analyzer::analyzer::UsageAnalyzer;
use swc_ecma_utils::{find_pat_ids, StmtLike};
use swc_ecma_visit::{noop_visit_mut_type, VisitMut, VisitMutWith, VisitWith};

use super::util::drop_invalid_stmts;
use crate::{
    program_data::{ProgramData, VarUsageInfoFlags},
    util::{is_hoisted_var_decl_without_init, sort::is_sorted_by, IsModuleItem, ModuleItemExt},
};

pub(super) struct DeclHoisterConfig {
    pub hoist_fns: bool,
    pub hoist_vars: bool,
    pub _top_level: bool,
}

pub(super) fn decl_hoister(config: DeclHoisterConfig, data: &ProgramData) -> Hoister {
    Hoister {
        config,
        changed: false,
        data,
    }
}

pub(super) struct Hoister<'a> {
    config: DeclHoisterConfig,
    changed: bool,
    data: &'a ProgramData,
}

impl Repeated for Hoister<'_> {
    fn changed(&self) -> bool {
        self.changed
    }

    fn reset(&mut self) {
        self.changed = false;
    }
}

impl Hoister<'_> {
    fn handle_stmt_likes<T>(&mut self, stmts: &mut Vec<T>)
    where
        T: StmtLike + IsModuleItem + ModuleItemExt,
        Vec<T>: for<'aa> VisitMutWith<Hoister<'aa>> + VisitWith<UsageAnalyzer<ProgramData>>,
    {
        stmts.visit_mut_children_with(self);
        let len = stmts.len();
        let should_hoist = !is_sorted_by(
            stmts.iter().map(|stmt| match stmt.as_stmt() {
                Some(stmt) => match stmt {
                    Stmt::Decl(Decl::Fn(..)) if self.config.hoist_fns => 1,
                    Stmt::Decl(Decl::Var(var)) if self.config.hoist_vars => {
                        let ids: Vec<Id> = find_pat_ids(&var.decls);

                        if ids.iter().any(|id| {
                            self.data
                                .vars
                                .get(id)
                                .map(|v| !v.flags.contains(VarUsageInfoFlags::USED_ABOVE_DECL))
                                .unwrap_or(false)
                        }) {
                            2
                        } else {
                            3
                        }
                    }
                    _ => 3,
                },
                None => 3,
            }),
            PartialOrd::partial_cmp,
        ) || (self.config.hoist_vars
            && if len >= *crate::LIGHT_TASK_PARALLELS {
                stmts.par_chunks(2).any(|stmts| {
                    is_hoisted_var_decl_without_init(&stmts[0])
                        && is_hoisted_var_decl_without_init(&stmts[1])
                })
            } else {
                stmts.windows(2).any(|stmts| {
                    is_hoisted_var_decl_without_init(&stmts[0])
                        && is_hoisted_var_decl_without_init(&stmts[1])
                })
            });

        if !should_hoist {
            return;
        }
        self.changed = true;

        let mut var_decls = Vec::new();
        let mut fn_decls = Vec::with_capacity(stmts.len());
        let mut new_stmts = Vec::with_capacity(stmts.len());
        let mut done = FxHashSet::default();

        let mut found_non_var_decl = false;
        for stmt in stmts.take() {
            match stmt.try_into_stmt() {
                Ok(stmt) => {
                    // Seaarch for variable declarations.
                    match stmt {
                        Stmt::Decl(Decl::Fn(..)) if self.config.hoist_fns => {
                            // Move functions to top.
                            fn_decls.push(T::from(stmt))
                        }

                        Stmt::Decl(Decl::Var(var))
                            if matches!(
                                &*var,
                                VarDecl {
                                    kind: VarDeclKind::Var,
                                    ..
                                }
                            ) && found_non_var_decl =>
                        {
                            let mut exprs = Vec::new();
                            for decl in var.decls {
                                let ids: Vec<Ident> = find_pat_ids(&decl.name);

                                for id in ids {
                                    if done.insert(id.to_id()) {
                                        // If the enclosing function declares parameter with same
                                        // name, we can drop a varaible.
                                        if decl.init.is_none()
                                            && self
                                                .data
                                                .vars
                                                .get(&id.to_id())
                                                .map(|v| {
                                                    v.flags.contains(
                                                        VarUsageInfoFlags::DECLARED_AS_FN_PARAM,
                                                    )
                                                })
                                                .unwrap_or(false)
                                        {
                                            continue;
                                        }

                                        var_decls.push(VarDeclarator {
                                            span: DUMMY_SP,
                                            name: id.into(),
                                            init: None,
                                            definite: false,
                                        })
                                    }
                                }

                                if let Some(init) = decl.init {
                                    //
                                    exprs.push(
                                        AssignExpr {
                                            span: decl.span,
                                            left: decl.name.try_into().unwrap(),
                                            op: op!("="),
                                            right: init,
                                        }
                                        .into(),
                                    );
                                }
                            }

                            if exprs.is_empty() {
                                continue;
                            }
                            new_stmts.push(T::from(
                                ExprStmt {
                                    span: var.span,
                                    expr: if exprs.len() == 1 {
                                        exprs.into_iter().next().unwrap()
                                    } else {
                                        SeqExpr {
                                            span: DUMMY_SP,
                                            exprs,
                                        }
                                        .into()
                                    },
                                }
                                .into(),
                            ))
                        }

                        Stmt::Decl(Decl::Var(v))
                            if matches!(
                                &*v,
                                VarDecl {
                                    kind: VarDeclKind::Var,
                                    ..
                                }
                            ) =>
                        {
                            // It can be merged because we didn't found normal statement.
                            //
                            // Code like
                            //
                            // var a = 1;
                            // var b = 3;
                            //
                            // will be merged.
                            var_decls.extend(v.decls.into_iter().filter(|decl| {
                                // We should preserve if init exists because
                                //
                                // var a = 2, a = 3;
                                //
                                // is valid javascript code.

                                let preserve = match &decl.name {
                                    Pat::Ident(name) => {
                                        // If the enclosing function declares parameter with same
                                        // name, we can drop a varaible. (If it's side-effect free).
                                        if decl.init.is_none()
                                            && self
                                                .data
                                                .vars
                                                .get(&name.to_id())
                                                .map(|v| {
                                                    v.flags.contains(
                                                        VarUsageInfoFlags::DECLARED_AS_FN_PARAM,
                                                    )
                                                })
                                                .unwrap_or(false)
                                        {
                                            return false;
                                        }

                                        done.insert(name.to_id())
                                    }
                                    _ => true,
                                };

                                preserve || decl.init.is_some()
                            }));
                        }

                        Stmt::Decl(Decl::Var(..)) => new_stmts.push(T::from(stmt)),
                        _ => {
                            if let Stmt::Throw(..) = stmt {
                                fn_decls.push(T::from(
                                    VarDecl {
                                        span: DUMMY_SP,
                                        kind: VarDeclKind::Var,
                                        declare: false,
                                        decls: var_decls.take(),
                                        ..Default::default()
                                    }
                                    .into(),
                                ));
                            }
                            found_non_var_decl = true;
                            new_stmts.push(T::from(stmt))
                        }
                    }
                }
                Err(stmt) => new_stmts.push(stmt),
            }
        }

        fn_decls.push(T::from(
            VarDecl {
                span: DUMMY_SP,
                kind: VarDeclKind::Var,
                declare: false,
                decls: var_decls,
                ..Default::default()
            }
            .into(),
        ));
        fn_decls.extend(new_stmts);

        drop_invalid_stmts(&mut fn_decls);

        *stmts = fn_decls;
    }
}

impl VisitMut for Hoister<'_> {
    noop_visit_mut_type!(fail);

    fn visit_mut_module_items(&mut self, stmts: &mut Vec<ModuleItem>) {
        self.handle_stmt_likes(stmts);
    }

    fn visit_mut_stmts(&mut self, stmts: &mut Vec<Stmt>) {
        self.handle_stmt_likes(stmts);
    }
}