From a51581bf947c5841324c6ad1568d5d000cf23069 Mon Sep 17 00:00:00 2001
From: Haled Odat <8566042+HalidOdat@users.noreply.github.com>
Date: Wed, 4 Oct 2023 01:17:35 +0200
Subject: [PATCH] Make environments opcodes use varying operands (#3340)

---
 boa_engine/src/builtins/eval/mod.rs           |  9 +--
 boa_engine/src/bytecompiler/class.rs          | 37 +++++-----
 boa_engine/src/bytecompiler/declarations.rs   | 13 ++--
 boa_engine/src/bytecompiler/env.rs            | 17 +++--
 boa_engine/src/bytecompiler/function.rs       |  9 +--
 .../src/bytecompiler/statement/block.rs       |  8 +-
 boa_engine/src/bytecompiler/statement/loop.rs | 74 ++++++++-----------
 .../src/bytecompiler/statement/switch.rs      |  7 +-
 boa_engine/src/bytecompiler/statement/try.rs  |  7 +-
 boa_engine/src/bytecompiler/statement/with.rs |  3 +-
 boa_engine/src/vm/code_block.rs               | 14 ++--
 boa_engine/src/vm/opcode/mod.rs               |  4 +-
 boa_engine/src/vm/opcode/push/environment.rs  | 32 ++++++--
 13 files changed, 117 insertions(+), 117 deletions(-)

diff --git a/boa_engine/src/builtins/eval/mod.rs b/boa_engine/src/builtins/eval/mod.rs
index 1eca3e654a0..6023687351e 100644
--- a/boa_engine/src/builtins/eval/mod.rs
+++ b/boa_engine/src/builtins/eval/mod.rs
@@ -232,16 +232,13 @@ impl Eval {
             context,
         );
 
-        compiler.push_compile_environment(strict);
-
-        let push_env = compiler.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+        let env_index = compiler.push_compile_environment(strict);
+        compiler.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
         compiler.eval_declaration_instantiation(&body, strict)?;
         compiler.compile_statement_list(body.statements(), true, false);
 
-        let env_index = compiler.pop_compile_environment();
-        compiler.patch_jump_with_target(push_env, env_index);
-
+        compiler.pop_compile_environment();
         compiler.emit_opcode(Opcode::PopEnvironment);
 
         let code_block = Gc::new(compiler.finish());
diff --git a/boa_engine/src/bytecompiler/class.rs b/boa_engine/src/bytecompiler/class.rs
index 88f8834b090..1bc57de76ca 100644
--- a/boa_engine/src/bytecompiler/class.rs
+++ b/boa_engine/src/bytecompiler/class.rs
@@ -26,13 +26,14 @@ impl ByteCompiler<'_, '_> {
     pub(crate) fn compile_class(&mut self, class: &Class, expression: bool) {
         let class_name = class.name().map_or(Sym::EMPTY_STRING, Identifier::sym);
 
-        let class_env: Option<super::Label> = match class.name() {
+        let class_env = match class.name() {
             Some(name) if class.has_binding_identifier() => {
-                self.push_compile_environment(false);
+                let env_index = self.push_compile_environment(false);
                 self.create_immutable_binding(name, true);
-                Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment))
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+                true
             }
-            _ => None,
+            _ => false,
         };
 
         let mut compiler = ByteCompiler::new(
@@ -43,7 +44,8 @@ impl ByteCompiler<'_, '_> {
             self.context,
         );
 
-        compiler.push_compile_environment(true);
+        // Function environment
+        let _ = compiler.push_compile_environment(true);
 
         if let Some(expr) = class.constructor() {
             compiler.length = expr.parameters().length();
@@ -59,15 +61,11 @@ impl ByteCompiler<'_, '_> {
 
             compiler.compile_statement_list(expr.body().statements(), false, false);
 
-            let env_index = compiler.pop_compile_environment();
-
-            if let Some(env_label) = env_label {
-                compiler.patch_jump_with_target(env_label, env_index);
+            if env_label {
                 compiler.pop_compile_environment();
             } else {
                 compiler.code_block_flags |= CodeBlockFlags::IS_CLASS_CONSTRUCTOR;
             }
-
             compiler.emit_opcode(Opcode::PushUndefined);
         } else {
             if class.super_ref().is_some() {
@@ -76,10 +74,10 @@ impl ByteCompiler<'_, '_> {
                 compiler.emit_opcode(Opcode::RestParameterPop);
                 compiler.emit_opcode(Opcode::PushUndefined);
             }
-            compiler.pop_compile_environment();
             compiler.code_block_flags |= CodeBlockFlags::IS_CLASS_CONSTRUCTOR;
         }
         compiler.emit_opcode(Opcode::SetReturnValue);
+        compiler.pop_compile_environment();
 
         let code = Gc::new(compiler.finish());
         let index = self.functions.len() as u32;
@@ -119,7 +117,7 @@ impl ByteCompiler<'_, '_> {
         let mut static_elements = Vec::new();
         let mut static_field_name_count = 0;
 
-        if class_env.is_some() {
+        if class_env {
             self.emit_opcode(Opcode::Dup);
             self.emit_binding(BindingOpcode::InitConst, class_name.into());
         }
@@ -282,7 +280,9 @@ impl ByteCompiler<'_, '_> {
                         self.current_environment.clone(),
                         self.context,
                     );
-                    field_compiler.push_compile_environment(true);
+
+                    // Function environment
+                    let _ = field_compiler.push_compile_environment(true);
                     if let Some(node) = field {
                         field_compiler.compile_expr(node, true);
                     } else {
@@ -314,7 +314,7 @@ impl ByteCompiler<'_, '_> {
                         self.current_environment.clone(),
                         self.context,
                     );
-                    field_compiler.push_compile_environment(true);
+                    let _ = field_compiler.push_compile_environment(true);
                     if let Some(node) = field {
                         field_compiler.compile_expr(node, true);
                     } else {
@@ -358,7 +358,7 @@ impl ByteCompiler<'_, '_> {
                         self.current_environment.clone(),
                         self.context,
                     );
-                    field_compiler.push_compile_environment(true);
+                    let _ = field_compiler.push_compile_environment(true);
                     if let Some(node) = field {
                         field_compiler.compile_expr(node, true);
                     } else {
@@ -393,7 +393,7 @@ impl ByteCompiler<'_, '_> {
                         self.current_environment.clone(),
                         self.context,
                     );
-                    compiler.push_compile_environment(true);
+                    let _ = compiler.push_compile_environment(true);
 
                     compiler.function_declaration_instantiation(
                         body,
@@ -589,9 +589,8 @@ impl ByteCompiler<'_, '_> {
         self.emit_opcode(Opcode::Swap);
         self.emit_opcode(Opcode::Pop);
 
-        if let Some(class_env) = class_env {
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(class_env, env_index);
+        if class_env {
+            self.pop_compile_environment();
             self.emit_opcode(Opcode::PopEnvironment);
         }
 
diff --git a/boa_engine/src/bytecompiler/declarations.rs b/boa_engine/src/bytecompiler/declarations.rs
index 5ea9269d1b6..2ebfdd7a405 100644
--- a/boa_engine/src/bytecompiler/declarations.rs
+++ b/boa_engine/src/bytecompiler/declarations.rs
@@ -1,5 +1,5 @@
 use crate::{
-    bytecompiler::{ByteCompiler, FunctionCompiler, FunctionSpec, Label, NodeKind},
+    bytecompiler::{ByteCompiler, FunctionCompiler, FunctionSpec, NodeKind},
     environments::BindingLocatorError,
     vm::{
         create_function_object_fast, create_generator_function_object, BindingOpcode,
@@ -809,8 +809,8 @@ impl ByteCompiler<'_, '_> {
         arrow: bool,
         strict: bool,
         generator: bool,
-    ) -> (Option<Label>, bool) {
-        let mut env_label = None;
+    ) -> (bool, bool) {
+        let mut env_label = false;
         let mut additional_env = false;
 
         // 1. Let calleeContext be the running execution context.
@@ -910,7 +910,7 @@ impl ByteCompiler<'_, '_> {
             // c. Let env be NewDeclarativeEnvironment(calleeEnv).
             // d. Assert: The VariableEnvironment of calleeContext is calleeEnv.
             // e. Set the LexicalEnvironment of calleeContext to env.
-            self.push_compile_environment(false);
+            let _ = self.push_compile_environment(false);
             additional_env = true;
         }
 
@@ -1030,8 +1030,9 @@ impl ByteCompiler<'_, '_> {
             //          visibility of declarations in the function body.
             // b. Let varEnv be NewDeclarativeEnvironment(env).
             // c. Set the VariableEnvironment of calleeContext to varEnv.
-            self.push_compile_environment(false);
-            env_label = Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment));
+            let env_index = self.push_compile_environment(false);
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            env_label = true;
 
             // d. Let instantiatedVarNames be a new empty List.
             let mut instantiated_var_names = Vec::new();
diff --git a/boa_engine/src/bytecompiler/env.rs b/boa_engine/src/bytecompiler/env.rs
index c817b5b7944..e85431b3ac1 100644
--- a/boa_engine/src/bytecompiler/env.rs
+++ b/boa_engine/src/bytecompiler/env.rs
@@ -6,29 +6,32 @@ use boa_ast::expression::Identifier;
 
 impl ByteCompiler<'_, '_> {
     /// Push either a new declarative or function environment on the compile time environment stack.
-    pub(crate) fn push_compile_environment(&mut self, function_scope: bool) {
+    #[must_use]
+    pub(crate) fn push_compile_environment(&mut self, function_scope: bool) -> u32 {
         self.current_open_environments_count += 1;
+
         self.current_environment = Rc::new(CompileTimeEnvironment::new(
             self.current_environment.clone(),
             function_scope,
         ));
+
+        let index = self.compile_environments.len() as u32;
+        self.compile_environments
+            .push(self.current_environment.clone());
+
+        index
     }
 
     /// Pops the top compile time environment and returns its index in the compile time environments array.
     #[track_caller]
-    pub(crate) fn pop_compile_environment(&mut self) -> u32 {
+    pub(crate) fn pop_compile_environment(&mut self) {
         self.current_open_environments_count -= 1;
-        let index = self.compile_environments.len() as u32;
-        self.compile_environments
-            .push(self.current_environment.clone());
 
         let outer = self
             .current_environment
             .outer()
             .expect("cannot pop the global environment");
         self.current_environment = outer;
-
-        index
     }
 
     /// Get the binding locator of the binding at bytecode compile time.
diff --git a/boa_engine/src/bytecompiler/function.rs b/boa_engine/src/bytecompiler/function.rs
index a7c39b94ec1..be072a6198a 100644
--- a/boa_engine/src/bytecompiler/function.rs
+++ b/boa_engine/src/bytecompiler/function.rs
@@ -100,12 +100,12 @@ impl FunctionCompiler {
 
         if let Some(binding_identifier) = self.binding_identifier {
             compiler.code_block_flags |= CodeBlockFlags::HAS_BINDING_IDENTIFIER;
-            compiler.push_compile_environment(false);
+            let _ = compiler.push_compile_environment(false);
             compiler.create_immutable_binding(binding_identifier.into(), self.strict);
         }
 
         // Function environment
-        compiler.push_compile_environment(true);
+        let _ = compiler.push_compile_environment(true);
 
         // Taken from:
         //  - 15.9.3 Runtime Semantics: EvaluateAsyncConciseBody: <https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncconcisebody>
@@ -155,9 +155,8 @@ impl FunctionCompiler {
 
         compiler.compile_statement_list(body.statements(), false, false);
 
-        if let Some(env_labels) = env_label {
-            let env_index = compiler.pop_compile_environment();
-            compiler.patch_jump_with_target(env_labels, env_index);
+        if env_label {
+            compiler.pop_compile_environment();
         }
 
         if additional_env {
diff --git a/boa_engine/src/bytecompiler/statement/block.rs b/boa_engine/src/bytecompiler/statement/block.rs
index 665d996ea02..5982dfd0731 100644
--- a/boa_engine/src/bytecompiler/statement/block.rs
+++ b/boa_engine/src/bytecompiler/statement/block.rs
@@ -4,15 +4,13 @@ use boa_ast::statement::Block;
 impl ByteCompiler<'_, '_> {
     /// Compile a [`Block`] `boa_ast` node
     pub(crate) fn compile_block(&mut self, block: &Block, use_expr: bool) {
-        self.push_compile_environment(false);
-        let push_env = self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+        let env_index = self.push_compile_environment(false);
+        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
         self.block_declaration_instantiation(block);
         self.compile_statement_list(block.statement_list(), use_expr, true);
 
-        let env_index = self.pop_compile_environment();
-        self.patch_jump_with_target(push_env, env_index);
-
+        self.pop_compile_environment();
         self.emit_opcode(Opcode::PopEnvironment);
     }
 }
diff --git a/boa_engine/src/bytecompiler/statement/loop.rs b/boa_engine/src/bytecompiler/statement/loop.rs
index 3196513e63a..4088a7e3b1c 100644
--- a/boa_engine/src/bytecompiler/statement/loop.rs
+++ b/boa_engine/src/bytecompiler/statement/loop.rs
@@ -22,8 +22,7 @@ impl ByteCompiler<'_, '_> {
         use_expr: bool,
     ) {
         let mut let_binding_indices = None;
-        let mut env_labels = None;
-        let mut iteration_env_labels = None;
+        let mut has_lexical_environment_binding = false;
 
         if let Some(init) = for_loop.init() {
             match init {
@@ -32,9 +31,9 @@ impl ByteCompiler<'_, '_> {
                     self.compile_var_decl(decl);
                 }
                 ForLoopInitializer::Lexical(decl) => {
-                    self.push_compile_environment(false);
-                    env_labels =
-                        Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment));
+                    let env_index = self.push_compile_environment(false);
+                    self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+                    has_lexical_environment_binding = true;
 
                     let names = bound_names(decl);
                     if decl.is_const() {
@@ -49,7 +48,7 @@ impl ByteCompiler<'_, '_> {
                             let index = self.get_or_insert_binding(binding);
                             indices.push(index);
                         }
-                        let_binding_indices = Some(indices);
+                        let_binding_indices = Some((indices, env_index));
                     }
                     self.compile_lexical_decl(decl);
                 }
@@ -67,13 +66,14 @@ impl ByteCompiler<'_, '_> {
             .expect("jump_control must exist as it was just pushed")
             .set_start_address(start_address);
 
-        if let Some(let_binding_indices) = let_binding_indices {
-            for index in &let_binding_indices {
+        if let Some((let_binding_indices, env_index)) = &let_binding_indices {
+            for index in let_binding_indices {
                 self.emit_with_varying_operand(Opcode::GetName, *index);
             }
+
             self.emit_opcode(Opcode::PopEnvironment);
-            iteration_env_labels =
-                Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment));
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, *env_index);
+
             for index in let_binding_indices.iter().rev() {
                 self.emit_with_varying_operand(Opcode::PutLexicalValue, *index);
             }
@@ -100,16 +100,10 @@ impl ByteCompiler<'_, '_> {
 
         self.patch_jump(exit);
         self.pop_loop_control_info();
-        if env_labels.is_some() {
-            self.emit_opcode(Opcode::PopEnvironment);
-        }
 
-        if let Some(env_labels) = env_labels {
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(env_labels, env_index);
-            if let Some(iteration_env_labels) = iteration_env_labels {
-                self.patch_jump_with_target(iteration_env_labels, env_index);
-            }
+        if has_lexical_environment_binding {
+            self.pop_compile_environment();
+            self.emit_opcode(Opcode::PopEnvironment);
         }
     }
 
@@ -136,16 +130,15 @@ impl ByteCompiler<'_, '_> {
         if initializer_bound_names.is_empty() {
             self.compile_expr(for_in_loop.target(), true);
         } else {
-            self.push_compile_environment(false);
-            let push_env = self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+            let env_index = self.push_compile_environment(false);
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
             for name in &initializer_bound_names {
                 self.create_mutable_binding(*name, false);
             }
             self.compile_expr(for_in_loop.target(), true);
 
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(push_env, env_index);
+            self.pop_compile_environment();
             self.emit_opcode(Opcode::PopEnvironment);
         }
 
@@ -162,12 +155,10 @@ impl ByteCompiler<'_, '_> {
 
         self.emit_opcode(Opcode::IteratorValue);
 
-        let iteration_environment = if initializer_bound_names.is_empty() {
-            None
-        } else {
-            self.push_compile_environment(false);
-            Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment))
-        };
+        if !initializer_bound_names.is_empty() {
+            let env_index = self.push_compile_environment(false);
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        }
 
         match for_in_loop.initializer() {
             IterableLoopInitializer::Identifier(ident) => {
@@ -219,9 +210,8 @@ impl ByteCompiler<'_, '_> {
 
         self.compile_stmt(for_in_loop.body(), use_expr, true);
 
-        if let Some(iteration_environment) = iteration_environment {
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(iteration_environment, env_index);
+        if !initializer_bound_names.is_empty() {
+            self.pop_compile_environment();
             self.emit_opcode(Opcode::PopEnvironment);
         }
 
@@ -252,16 +242,15 @@ impl ByteCompiler<'_, '_> {
         if initializer_bound_names.is_empty() {
             self.compile_expr(for_of_loop.iterable(), true);
         } else {
-            self.push_compile_environment(false);
-            let push_env = self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+            let env_index = self.push_compile_environment(false);
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
             for name in &initializer_bound_names {
                 self.create_mutable_binding(*name, false);
             }
             self.compile_expr(for_of_loop.iterable(), true);
 
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(push_env, env_index);
+            self.pop_compile_environment();
             self.emit_opcode(Opcode::PopEnvironment);
         }
 
@@ -290,11 +279,9 @@ impl ByteCompiler<'_, '_> {
         let exit = self.jump_if_true();
         self.emit_opcode(Opcode::IteratorValue);
 
-        let iteration_environment = if initializer_bound_names.is_empty() {
-            None
-        } else {
-            self.push_compile_environment(false);
-            Some(self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment))
+        if !initializer_bound_names.is_empty() {
+            let env_index = self.push_compile_environment(false);
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
         };
 
         let mut handler_index = None;
@@ -388,9 +375,8 @@ impl ByteCompiler<'_, '_> {
 
         self.compile_stmt(for_of_loop.body(), use_expr, true);
 
-        if let Some(iteration_environment) = iteration_environment {
-            let env_index = self.pop_compile_environment();
-            self.patch_jump_with_target(iteration_environment, env_index);
+        if !initializer_bound_names.is_empty() {
+            self.pop_compile_environment();
             self.emit_opcode(Opcode::PopEnvironment);
         }
 
diff --git a/boa_engine/src/bytecompiler/statement/switch.rs b/boa_engine/src/bytecompiler/statement/switch.rs
index 46df6c692f9..fd007840671 100644
--- a/boa_engine/src/bytecompiler/statement/switch.rs
+++ b/boa_engine/src/bytecompiler/statement/switch.rs
@@ -6,8 +6,8 @@ impl ByteCompiler<'_, '_> {
     pub(crate) fn compile_switch(&mut self, switch: &Switch, use_expr: bool) {
         self.compile_expr(switch.val(), true);
 
-        self.push_compile_environment(false);
-        let push_env = self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+        let env_index = self.push_compile_environment(false);
+        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
         self.block_declaration_instantiation(switch);
 
@@ -50,8 +50,7 @@ impl ByteCompiler<'_, '_> {
 
         self.pop_switch_control_info();
 
-        let env_index = self.pop_compile_environment();
-        self.patch_jump_with_target(push_env, env_index);
+        self.pop_compile_environment();
         self.emit_opcode(Opcode::PopEnvironment);
     }
 }
diff --git a/boa_engine/src/bytecompiler/statement/try.rs b/boa_engine/src/bytecompiler/statement/try.rs
index fcaffc4d089..07a6bb1b1c4 100644
--- a/boa_engine/src/bytecompiler/statement/try.rs
+++ b/boa_engine/src/bytecompiler/statement/try.rs
@@ -111,8 +111,8 @@ impl ByteCompiler<'_, '_> {
     pub(crate) fn compile_catch_stmt(&mut self, catch: &Catch, _has_finally: bool, use_expr: bool) {
         // stack: exception
 
-        self.push_compile_environment(false);
-        let push_env = self.emit_opcode_with_operand(Opcode::PushDeclarativeEnvironment);
+        let env_index = self.push_compile_environment(false);
+        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
 
         if let Some(binding) = catch.parameter() {
             match binding {
@@ -133,8 +133,7 @@ impl ByteCompiler<'_, '_> {
 
         self.compile_catch_finally_block(catch.block(), use_expr);
 
-        let env_index = self.pop_compile_environment();
-        self.patch_jump_with_target(push_env, env_index);
+        self.pop_compile_environment();
         self.emit_opcode(Opcode::PopEnvironment);
     }
 
diff --git a/boa_engine/src/bytecompiler/statement/with.rs b/boa_engine/src/bytecompiler/statement/with.rs
index 0b63edee268..db804296776 100644
--- a/boa_engine/src/bytecompiler/statement/with.rs
+++ b/boa_engine/src/bytecompiler/statement/with.rs
@@ -5,7 +5,8 @@ impl ByteCompiler<'_, '_> {
     /// Compile a [`With`] `boa_ast` node
     pub(crate) fn compile_with(&mut self, with: &With, use_expr: bool) {
         self.compile_expr(with.expression(), true);
-        self.push_compile_environment(false);
+
+        let _ = self.push_compile_environment(false);
         self.emit_opcode(Opcode::PushObjectEnvironment);
 
         self.compile_stmt(with.statement(), use_expr, true);
diff --git a/boa_engine/src/vm/code_block.rs b/boa_engine/src/vm/code_block.rs
index a88d3506733..df17b441e38 100644
--- a/boa_engine/src/vm/code_block.rs
+++ b/boa_engine/src/vm/code_block.rs
@@ -363,7 +363,7 @@ impl CodeBlock {
             | Instruction::ConcatToString { value_count: value } => value.value().to_string(),
             Instruction::PushDeclarativeEnvironment {
                 compile_environments_index,
-            } => compile_environments_index.to_string(),
+            } => compile_environments_index.value().to_string(),
             Instruction::CopyDataProperties {
                 excluded_key_count: value1,
                 excluded_key_count_computed: value2,
@@ -1062,7 +1062,7 @@ impl JsObject {
 
         let env_fp = context.vm.environments.len() as u32;
 
-        let mut last_env = code.compile_environments.len() - 1;
+        let mut last_env = 0;
 
         if code.has_binding_identifier() {
             let index = context
@@ -1073,7 +1073,7 @@ impl JsObject {
                 .vm
                 .environments
                 .put_lexical_value(index, 0, self.clone().into());
-            last_env -= 1;
+            last_env += 1;
         }
 
         context.vm.environments.push_function(
@@ -1082,7 +1082,7 @@ impl JsObject {
         );
 
         if code.has_parameters_env_bindings() {
-            last_env -= 1;
+            last_env += 1;
             context
                 .vm
                 .environments
@@ -1204,7 +1204,7 @@ impl JsObject {
 
         let new_target = this_target.as_object().expect("must be object");
 
-        let mut last_env = code.compile_environments.len() - 1;
+        let mut last_env = 0;
 
         if code.has_binding_identifier() {
             let index = context
@@ -1215,7 +1215,7 @@ impl JsObject {
                 .vm
                 .environments
                 .put_lexical_value(index, 0, self.clone().into());
-            last_env -= 1;
+            last_env += 1;
         }
 
         context.vm.environments.push_function(
@@ -1232,7 +1232,7 @@ impl JsObject {
         let environment = context.vm.environments.current();
 
         if code.has_parameters_env_bindings() {
-            last_env -= 1;
+            last_env += 1;
             context
                 .vm
                 .environments
diff --git a/boa_engine/src/vm/opcode/mod.rs b/boa_engine/src/vm/opcode/mod.rs
index 757a4995524..c7279be5fb1 100644
--- a/boa_engine/src/vm/opcode/mod.rs
+++ b/boa_engine/src/vm/opcode/mod.rs
@@ -1738,10 +1738,10 @@ generate_opcodes! {
 
     /// Push a declarative environment.
     ///
-    /// Operands: compile_environments_index: `u32`
+    /// Operands: compile_environments_index: `VaryingOperand`
     ///
     /// Stack: **=>**
-    PushDeclarativeEnvironment { compile_environments_index: u32 },
+    PushDeclarativeEnvironment { compile_environments_index: VaryingOperand },
 
     /// Push an object environment.
     ///
diff --git a/boa_engine/src/vm/opcode/push/environment.rs b/boa_engine/src/vm/opcode/push/environment.rs
index e1776433b18..0f80166fd62 100644
--- a/boa_engine/src/vm/opcode/push/environment.rs
+++ b/boa_engine/src/vm/opcode/push/environment.rs
@@ -12,17 +12,36 @@ use boa_gc::Gc;
 #[derive(Debug, Clone, Copy)]
 pub(crate) struct PushDeclarativeEnvironment;
 
+impl PushDeclarativeEnvironment {
+    #[allow(clippy::unnecessary_wraps)]
+    fn operation(
+        context: &mut Context<'_>,
+        compile_environments_index: usize,
+    ) -> JsResult<CompletionType> {
+        let compile_environment =
+            context.vm.frame().code_block.compile_environments[compile_environments_index].clone();
+        context.vm.environments.push_lexical(compile_environment);
+        Ok(CompletionType::Normal)
+    }
+}
+
 impl Operation for PushDeclarativeEnvironment {
     const NAME: &'static str = "PushDeclarativeEnvironment";
     const INSTRUCTION: &'static str = "INST - PushDeclarativeEnvironment";
 
     fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let compile_environments_index = context.vm.read::<u32>();
-        let compile_environment = context.vm.frame().code_block.compile_environments
-            [compile_environments_index as usize]
-            .clone();
-        context.vm.environments.push_lexical(compile_environment);
-        Ok(CompletionType::Normal)
+        let compile_environments_index = context.vm.read::<u8>() as usize;
+        Self::operation(context, compile_environments_index)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let compile_environments_index = context.vm.read::<u16>() as usize;
+        Self::operation(context, compile_environments_index)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let compile_environments_index = context.vm.read::<u32>() as usize;
+        Self::operation(context, compile_environments_index)
     }
 }
 
@@ -98,7 +117,6 @@ impl Operation for PopPrivateEnvironment {
 
     fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
         context.vm.environments.pop_private();
-
         Ok(CompletionType::Normal)
     }
 }