From 858bcac4c7baa26a7a31310d5d220f60a43f5cd9 Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Mon, 14 Mar 2022 02:34:01 +0000
Subject: [PATCH] LibJS/Bytecode: Unwind environments before block terminating
 instruction

When we reach a block terminating instruction (e.g. Break, Throw),
we cannot generate anymore instructions after it. This would not allow
us to leave any lexical/variable environments.

This uses the mechanism introduced in ba9c49 to unwind environments
when we encounter these instructions.
---
 .../Libraries/LibJS/Bytecode/Generator.cpp    | 27 +++++++++++++++++
 Userland/Libraries/LibJS/Bytecode/Generator.h | 29 ++++++-------------
 2 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.cpp b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
index cc79dde944..31e1a4fe61 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
@@ -76,6 +76,33 @@ Label Generator::nearest_continuable_scope() const
     return m_continuable_scopes.last();
 }
 
+void Generator::begin_variable_scope(BindingMode mode, SurroundingScopeKind kind)
+{
+    m_variable_scopes.append({ kind, mode, {} });
+    if (mode != BindingMode::Global) {
+        start_boundary(mode == BindingMode::Lexical ? BlockBoundaryType::LeaveLexicalEnvironment : BlockBoundaryType::LeaveVariableEnvironment);
+        emit<Bytecode::Op::CreateEnvironment>(
+            mode == BindingMode::Lexical
+                ? Bytecode::Op::EnvironmentMode::Lexical
+                : Bytecode::Op::EnvironmentMode::Var);
+    }
+}
+
+void Generator::end_variable_scope()
+{
+    auto mode = m_variable_scopes.take_last().mode;
+    if (mode != BindingMode::Global) {
+        end_boundary(mode == BindingMode::Lexical ? BlockBoundaryType::LeaveLexicalEnvironment : BlockBoundaryType::LeaveVariableEnvironment);
+
+        if (!m_current_basic_block->is_terminated()) {
+            emit<Bytecode::Op::LeaveEnvironment>(
+                mode == BindingMode::Lexical
+                    ? Bytecode::Op::EnvironmentMode::Lexical
+                    : Bytecode::Op::EnvironmentMode::Var);
+        }
+    }
+}
+
 void Generator::begin_continuable_scope(Label continue_target)
 {
     m_continuable_scopes.append(continue_target);
diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.h b/Userland/Libraries/LibJS/Bytecode/Generator.h
index 80db80d34f..91662a9aea 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.h
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.h
@@ -150,31 +150,16 @@ public:
         }
         return false;
     }
-    void begin_variable_scope(BindingMode mode = BindingMode::Lexical, SurroundingScopeKind kind = SurroundingScopeKind::Block)
-    {
-        m_variable_scopes.append({ kind, mode, {} });
-        if (mode != BindingMode::Global) {
-            emit<Bytecode::Op::CreateEnvironment>(
-                mode == BindingMode::Lexical
-                    ? Bytecode::Op::EnvironmentMode::Lexical
-                    : Bytecode::Op::EnvironmentMode::Var);
-        }
-    }
-    void end_variable_scope()
-    {
-        auto mode = m_variable_scopes.take_last().mode;
-        if (mode != BindingMode::Global && !m_current_basic_block->is_terminated()) {
-            emit<Bytecode::Op::LeaveEnvironment>(
-                mode == BindingMode::Lexical
-                    ? Bytecode::Op::EnvironmentMode::Lexical
-                    : Bytecode::Op::EnvironmentMode::Var);
-        }
-    }
+
+    void begin_variable_scope(BindingMode mode = BindingMode::Lexical, SurroundingScopeKind kind = SurroundingScopeKind::Block);
+    void end_variable_scope();
 
     enum class BlockBoundaryType {
         Break,
         Continue,
         Unwind,
+        LeaveLexicalEnvironment,
+        LeaveVariableEnvironment,
     };
     template<typename OpType>
     void perform_needed_unwinds(bool is_break_node = false) requires(OpType::IsTerminator)
@@ -191,6 +176,10 @@ public:
                 break;
             if (boundary == BlockBoundaryType::Unwind)
                 emit<Bytecode::Op::LeaveUnwindContext>();
+            else if (boundary == BlockBoundaryType::LeaveLexicalEnvironment)
+                emit<Bytecode::Op::LeaveEnvironment>(Bytecode::Op::EnvironmentMode::Lexical);
+            else if (boundary == BlockBoundaryType::LeaveVariableEnvironment)
+                emit<Bytecode::Op::LeaveEnvironment>(Bytecode::Op::EnvironmentMode::Var);
         }
     }