feat(minifier): inline literal values across multiple scopes

crates/oxc_minifier/src/peephole/inline.rs

@@ -1,5 +1,5 @@
 use oxc_ast::ast::*;
-use oxc_ecmascript::constant_evaluation::{ConstantEvaluation, ConstantValue};
+use oxc_ecmascript::constant_evaluation::{ConstantEvaluation, ConstantValue, IsLiteralValue};
 use oxc_semantic::{ScopeFlags, ScopeId, SymbolId};
 use oxc_span::GetSpan;
 use oxc_traverse::Ancestor;
@@ -111,6 +111,8 @@ impl<'a> PeepholeOptimizations {
             } else {
                 SymbolValue::Primitive(value)
             }
+        } else if init.is_some_and(|init| init.is_literal_value(true, ctx)) {
+            SymbolValue::ScopedLiteral
         } else {
             return;
         };
@@ -153,6 +155,15 @@ impl<'a> PeepholeOptimizations {
                     ctx.state.changed = true;
                 }
             }
+            SymbolValue::ScopedLiteral => {
+                if symbol_value.read_references_count == 1
+                    && symbol_value.scope_id.is_some_and(|declared_scope_id| {
+                        Self::is_referenced_in_same_non_control_scope(declared_scope_id, ctx)
+                    })
+                {
+                    ctx.state.symbol_values.mark_symbol_inlineable(symbol_id);
+                }
+            }
             SymbolValue::Unknown => {}
         }
     }
@@ -180,6 +191,23 @@ impl<'a> PeepholeOptimizations {
             })
             .unwrap_or_default()
     }
+
+    fn is_referenced_in_same_non_control_scope(
+        declared_scope_id: ScopeId,
+        ctx: &Ctx<'a, '_>,
+    ) -> bool {
+        #[expect(clippy::unnecessary_find_map)] // TODO
+        ctx.scoping()
+            .scope_ancestors(ctx.current_scope_id())
+            .find_map(|scope_id| {
+                if declared_scope_id == scope_id {
+                    return Some(true);
+                }
+                // TODO: allow non-control scope
+                Some(false)
+            })
+            .unwrap_or_default()
+    }
 }
 
 #[cfg(test)]

crates/oxc_minifier/src/peephole/mod.rs

@@ -16,9 +16,9 @@ mod remove_unused_expression;
 mod replace_known_methods;
 mod substitute_alternate_syntax;
 
-use oxc_ast_visit::Visit;
-use oxc_semantic::ReferenceId;
-use rustc_hash::FxHashSet;
+use oxc_ast_visit::{Visit, VisitMut, walk_mut};
+use oxc_semantic::{ReferenceId, Scoping, SymbolId};
+use rustc_hash::{FxBuildHasher, FxHashMap, FxHashSet};
 
 use oxc_allocator::Vec;
 use oxc_ast::ast::*;
@@ -115,6 +115,12 @@ impl<'a> Traverse<'a, MinifierState<'a>> for PeepholeOptimizations {
 
     fn exit_program(&mut self, program: &mut Program<'a>, ctx: &mut TraverseCtx<'a>) {
         self.changed = ctx.state.changed;
+        let inlineable_symbols = ctx.state.symbol_values.get_inlineable_symbols();
+        if !inlineable_symbols.is_empty() {
+            let mut value_inliner = ValueInliner::new(inlineable_symbols, ctx.scoping());
+            value_inliner.visit_program(program);
+            self.changed = true;
+        }
         if self.changed {
             // Remove unused references by visiting the AST again and diff the collected references.
             let refs_before =
@@ -525,3 +531,47 @@ impl<'a> Visit<'a> for ReferencesCounter {
         self.refs.insert(reference_id);
     }
 }
+
+struct ValueInliner<'a, 'b> {
+    scoping: &'b Scoping,
+    inlineable_symbols: &'b FxHashSet<SymbolId>,
+    values: FxHashMap<SymbolId, Expression<'a>>,
+}
+
+impl<'b> ValueInliner<'_, 'b> {
+    pub fn new(inlineable_symbols: &'b FxHashSet<SymbolId>, scoping: &'b Scoping) -> Self {
+        Self {
+            scoping,
+            inlineable_symbols,
+            values: FxHashMap::with_capacity_and_hasher(inlineable_symbols.len(), FxBuildHasher),
+        }
+    }
+}
+
+impl<'a> VisitMut<'a> for ValueInliner<'a, '_> {
+    fn visit_variable_declarators(&mut self, decls: &mut Vec<'a, VariableDeclarator<'a>>) {
+        walk_mut::walk_variable_declarators(self, decls);
+        for decl in decls {
+            if let BindingPatternKind::BindingIdentifier(id) = &mut decl.id.kind {
+                let symbol_id = id.symbol_id();
+                if self.inlineable_symbols.contains(&symbol_id) {
+                    self.values.insert(
+                        symbol_id,
+                        decl.init.take().expect("Expected initializer for inlineable symbols"),
+                    );
+                }
+            }
+        }
+    }
+
+    fn visit_expression(&mut self, it: &mut Expression<'a>) {
+        walk_mut::walk_expression(self, it);
+        if let Expression::Identifier(id) = it {
+            if let Some(symbol_id) = self.scoping.get_reference(id.reference_id()).symbol_id()
+                && let Some(value) = self.values.remove(&symbol_id)
+            {
+                *it = value;
+            }
+        }
+    }
+}

crates/oxc_minifier/src/symbol_value.rs

@@ -1,4 +1,4 @@
-use rustc_hash::FxHashMap;
+use rustc_hash::{FxHashMap, FxHashSet};
 
 use oxc_ecmascript::constant_evaluation::ConstantValue;
 use oxc_syntax::{scope::ScopeId, symbol::SymbolId};
@@ -10,6 +10,9 @@ pub enum SymbolValue<'a> {
     /// Initialized primitive value.
     /// This can be inlined within the same scope after the variable is declared.
     ScopedPrimitive(ConstantValue<'a>),
+    /// Initialized scoped literal value.
+    /// This can be inlined within the same scope after the variable is declared if it's only used once.
+    ScopedLiteral,
     #[default]
     Unknown,
 }
@@ -36,18 +39,25 @@ pub struct SymbolInformation<'a> {
 #[derive(Debug, Default)]
 pub struct SymbolInformationMap<'a> {
     values: FxHashMap<SymbolId, SymbolInformation<'a>>,
+    inlineable_symbols: FxHashSet<SymbolId>,
 }
 
 impl<'a> SymbolInformationMap<'a> {
     pub fn clear(&mut self) {
         self.values.clear();
+        self.inlineable_symbols.clear();
     }
 
     pub fn init_value(&mut self, symbol_id: SymbolId, symbol_value: SymbolInformation<'a>) {
         self.values.insert(symbol_id, symbol_value);
     }
 
-    pub fn set_value(&mut self, symbol_id: SymbolId, symbol_value: SymbolValue<'a>, scope_id: ScopeId) {
+    pub fn set_value(
+        &mut self,
+        symbol_id: SymbolId,
+        symbol_value: SymbolValue<'a>,
+        scope_id: ScopeId,
+    ) {
         let info = self.values.get_mut(&symbol_id).expect("symbol value must exist");
         info.value = symbol_value;
         info.scope_id = Some(scope_id);
@@ -56,4 +66,12 @@ impl<'a> SymbolInformationMap<'a> {
     pub fn get_symbol_value(&self, symbol_id: SymbolId) -> Option<&SymbolInformation<'a>> {
         self.values.get(&symbol_id)
     }
+
+    pub fn mark_symbol_inlineable(&mut self, symbol_id: SymbolId) {
+        self.inlineable_symbols.insert(symbol_id);
+    }
+
+    pub fn get_inlineable_symbols(&self) -> &FxHashSet<SymbolId> {
+        &self.inlineable_symbols
+    }
 }

tasks/minsize/minsize.snap

@@ -1,27 +1,27 @@
            | Oxc        | ESBuild    | Oxc        | ESBuild    |
 Original   | minified   | minified   | gzip       | gzip       | Iterations | File      
 -------------------------------------------------------------------------------------
-72.14 kB   | 23.14 kB   | 23.70 kB   | 8.32 kB    | 8.54 kB    |          2 | react.development.js 
+72.14 kB   | 23.12 kB   | 23.70 kB   | 8.32 kB    | 8.54 kB    |          2 | react.development.js 
 
-173.90 kB  | 59.33 kB   | 59.82 kB   | 19.08 kB   | 19.33 kB   |          2 | moment.js  
+173.90 kB  | 59.27 kB   | 59.82 kB   | 19.04 kB   | 19.33 kB   |          2 | moment.js  
 
-287.63 kB  | 89.28 kB   | 90.07 kB   | 30.93 kB   | 31.95 kB   |          2 | jquery.js  
+287.63 kB  | 89.27 kB   | 90.07 kB   | 30.93 kB   | 31.95 kB   |          2 | jquery.js  
 
-342.15 kB  | 116.94 kB  | 118.14 kB  | 43.14 kB   | 44.37 kB   |          2 | vue.js     
+342.15 kB  | 116.92 kB  | 118.14 kB  | 43.13 kB   | 44.37 kB   |          2 | vue.js     
 
-544.10 kB  | 71.89 kB   | 72.48 kB   | 25.48 kB   | 26.20 kB   |          2 | lodash.js  
+544.10 kB  | 71.89 kB   | 72.48 kB   | 25.49 kB   | 26.20 kB   |          2 | lodash.js  
 
-555.77 kB  | 270.62 kB  | 270.13 kB  | 88.13 kB   | 90.80 kB   |          2 | d3.js      
+555.77 kB  | 270.61 kB  | 270.13 kB  | 88.14 kB   | 90.80 kB   |          2 | d3.js      
 
-1.01 MB    | 439.47 kB  | 458.89 kB  | 122.10 kB  | 126.71 kB  |          4 | bundle.min.js 
+1.01 MB    | 439.45 kB  | 458.89 kB  | 122.08 kB  | 126.71 kB  |          4 | bundle.min.js 
 
-1.25 MB    | 644.77 kB  | 646.76 kB  | 158.99 kB  | 163.73 kB  |          2 | three.js   
+1.25 MB    | 644.71 kB  | 646.76 kB  | 158.90 kB  | 163.73 kB  |          3 | three.js   
 
-2.14 MB    | 713.33 kB  | 724.14 kB  | 160.72 kB  | 181.07 kB  |          2 | victory.js 
+2.14 MB    | 711.05 kB  | 724.14 kB  | 159.75 kB  | 181.07 kB  |          5 | victory.js 
 
-3.20 MB    | 1.00 MB    | 1.01 MB    | 322.70 kB  | 331.56 kB  |          3 | echarts.js 
+3.20 MB    | 1.00 MB    | 1.01 MB    | 322.78 kB  | 331.56 kB  |          3 | echarts.js 
 
-6.69 MB    | 2.22 MB    | 2.31 MB    | 458.78 kB  | 488.28 kB  |          4 | antd.js    
+6.69 MB    | 2.22 MB    | 2.31 MB    | 457.74 kB  | 488.28 kB  |          4 | antd.js    
 
-10.95 MB   | 3.34 MB    | 3.49 MB    | 854.83 kB  | 915.50 kB  |          4 | typescript.js 
+10.95 MB   | 3.34 MB    | 3.49 MB    | 854.56 kB  | 915.50 kB  |          4 | typescript.js 
 

tasks/track_memory_allocations/allocs_minifier.snap

@@ -2,7 +2,7 @@ File                       | File size      || Sys allocs     | Sys reallocs   |
 -------------------------------------------------------------------------------------------------------------------------------------------
 RadixUIAdoptionSection.jsx | 2.52 kB        ||             85 |              4 ||             20 |              6 | 688 B         
 
-pdf.mjs                    | 567.30 kB      ||          19599 |           2910 ||          47403 |           7782 | 1.624 MB      
+pdf.mjs                    | 567.30 kB      ||          19786 |           2914 ||          56295 |          10084 | 1.998 MB      
 
-antd.js                    | 6.69 MB        ||          99745 |          13520 ||         331917 |          70164 | 17.367 MB     
+antd.js                    | 6.69 MB        ||          98808 |          13511 ||         331792 |          70073 | 17.306 MB