From 1414c7b049c5a8858f400a5e677cd20894463b32 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Sun, 13 Jun 2021 20:40:20 +0430
Subject: LibJS: Add a basic pass manager and add some basic passes

This commit adds a bunch of passes, the most interesting of which is a
pass that merges blocks together, and a pass that places blocks that
flow into each other next to each other, and a very simply pass that
removes duplicate basic blocks.
Note that this does not remove the jump at the end of each block in that
pass to avoid scope creep in the passes.
---
 Meta/Lagom/CMakeLists.txt                          |   3 +-
 Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp   |   1 +
 Userland/Libraries/LibJS/Bytecode/Instruction.h    |   2 +
 Userland/Libraries/LibJS/Bytecode/Interpreter.cpp  |  34 +++++
 Userland/Libraries/LibJS/Bytecode/Interpreter.h    |   9 ++
 Userland/Libraries/LibJS/Bytecode/Label.h          |   6 +-
 Userland/Libraries/LibJS/Bytecode/Op.cpp           |  30 ++++
 Userland/Libraries/LibJS/Bytecode/Op.h             | 127 ++++++++++++----
 Userland/Libraries/LibJS/Bytecode/Pass/DumpCFG.cpp |  27 ++++
 .../Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp  | 102 +++++++++++++
 .../Libraries/LibJS/Bytecode/Pass/MergeBlocks.cpp  | 165 +++++++++++++++++++++
 .../Libraries/LibJS/Bytecode/Pass/PlaceBlocks.cpp  |  54 +++++++
 .../LibJS/Bytecode/Pass/UnifySameBlocks.cpp        |  62 ++++++++
 Userland/Libraries/LibJS/Bytecode/PassManager.h    | 141 ++++++++++++++++++
 Userland/Libraries/LibJS/CMakeLists.txt            |   5 +
 .../Libraries/LibJS/Runtime/ScriptFunction.cpp     |   4 +
 Userland/Utilities/js.cpp                          |   9 ++
 17 files changed, 751 insertions(+), 30 deletions(-)
 create mode 100644 Userland/Libraries/LibJS/Bytecode/Pass/DumpCFG.cpp
 create mode 100644 Userland/Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp
 create mode 100644 Userland/Libraries/LibJS/Bytecode/Pass/MergeBlocks.cpp
 create mode 100644 Userland/Libraries/LibJS/Bytecode/Pass/PlaceBlocks.cpp
 create mode 100644 Userland/Libraries/LibJS/Bytecode/Pass/UnifySameBlocks.cpp
 create mode 100644 Userland/Libraries/LibJS/Bytecode/PassManager.h

diff --git a/Meta/Lagom/CMakeLists.txt b/Meta/Lagom/CMakeLists.txt
index 730d2bb549..1a350fdcbd 100644
--- a/Meta/Lagom/CMakeLists.txt
+++ b/Meta/Lagom/CMakeLists.txt
@@ -69,6 +69,7 @@ file(GLOB LIBMARKDOWN_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibMar
 file(GLOB LIBX86_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibX86/*.cpp")
 file(GLOB LIBJS_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibJS/*.cpp")
 file(GLOB LIBJS_SUBDIR_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibJS/*/*.cpp")
+file(GLOB LIBJS_SUBSUBDIR_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibJS/*/*/*.cpp")
 file(GLOB LIBCOMPRESS_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibCompress/*.cpp")
 file(GLOB LIBCOMPRESS_TESTS CONFIGURE_DEPENDS "../../Tests/LibCompress/*.cpp")
 file(GLOB LIBCRYPTO_SOURCES CONFIGURE_DEPENDS "../../Userland/Libraries/LibCrypto/*.cpp")
@@ -92,7 +93,7 @@ file(GLOB LIBTEST_MAIN CONFIGURE_DEPENDS "../../Userland/Libraries/LibTest/TestM
 
 set(LAGOM_REGEX_SOURCES ${LIBREGEX_LIBC_SOURCES} ${LIBREGEX_SOURCES})
 set(LAGOM_CORE_SOURCES ${AK_SOURCES} ${LIBCORE_SOURCES})
-set(LAGOM_MORE_SOURCES ${LIBARCHIVE_SOURCES} ${LIBAUDIO_SOURCES} ${LIBELF_SOURCES} ${LIBIPC_SOURCES} ${LIBLINE_SOURCES} ${LIBJS_SOURCES} ${LIBJS_SUBDIR_SOURCES} ${LIBX86_SOURCES} ${LIBCRYPTO_SOURCES} ${LIBCOMPRESS_SOURCES} ${LIBCRYPTO_SUBDIR_SOURCES} ${LIBCRYPTO_SUBSUBDIR_SOURCES} ${LIBTLS_SOURCES} ${LIBTTF_SOURCES} ${LIBTEXTCODEC_SOURCES} ${LIBMARKDOWN_SOURCES} ${LIBGEMINI_SOURCES} ${LIBGFX_SOURCES} ${LIBGUI_GML_SOURCES} ${LIBHTTP_SOURCES} ${LAGOM_REGEX_SOURCES} ${SHELL_SOURCES} ${LIBSQL_SOURCES} ${LIBWASM_SOURCES} ${LIBIMAP_SOURCES})
+set(LAGOM_MORE_SOURCES ${LIBARCHIVE_SOURCES} ${LIBAUDIO_SOURCES} ${LIBELF_SOURCES} ${LIBIPC_SOURCES} ${LIBLINE_SOURCES} ${LIBJS_SOURCES} ${LIBJS_SUBDIR_SOURCES} ${LIBJS_SUBSUBDIR_SOURCES} ${LIBX86_SOURCES} ${LIBCRYPTO_SOURCES} ${LIBCOMPRESS_SOURCES} ${LIBCRYPTO_SUBDIR_SOURCES} ${LIBCRYPTO_SUBSUBDIR_SOURCES} ${LIBTLS_SOURCES} ${LIBTTF_SOURCES} ${LIBTEXTCODEC_SOURCES} ${LIBMARKDOWN_SOURCES} ${LIBGEMINI_SOURCES} ${LIBGFX_SOURCES} ${LIBGUI_GML_SOURCES} ${LIBHTTP_SOURCES} ${LAGOM_REGEX_SOURCES} ${SHELL_SOURCES} ${LIBSQL_SOURCES} ${LIBWASM_SOURCES} ${LIBIMAP_SOURCES})
 set(LAGOM_TEST_SOURCES ${LIBTEST_SOURCES})
 
 # FIXME: This is a hack, because the lagom stuff can be build individually or
diff --git a/Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp b/Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp
index 0182d4412f..8bac7aa06a 100644
--- a/Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp
@@ -66,6 +66,7 @@ void BasicBlock::grow(size_t additional_size)
 
 void InstructionStreamIterator::operator++()
 {
+    VERIFY(!at_end());
     m_offset += dereference().length();
 }
 
diff --git a/Userland/Libraries/LibJS/Bytecode/Instruction.h b/Userland/Libraries/LibJS/Bytecode/Instruction.h
index 11c9b6b745..ac0e8de028 100644
--- a/Userland/Libraries/LibJS/Bytecode/Instruction.h
+++ b/Userland/Libraries/LibJS/Bytecode/Instruction.h
@@ -80,10 +80,12 @@ public:
 #undef __BYTECODE_OP
     };
 
+    bool is_terminator() const;
     Type type() const { return m_type; }
     size_t length() const;
     String to_string(Bytecode::Executable const&) const;
     void execute(Bytecode::Interpreter&) const;
+    void replace_references(BasicBlock const&, BasicBlock const&);
     static void destroy(Instruction&);
 
 protected:
diff --git a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
index eb63d3f895..4d4441cd7d 100644
--- a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
@@ -165,4 +165,38 @@ void Interpreter::continue_pending_unwind(Label const& resume_label)
         jump(resume_label);
     }
 }
+
+AK::Array<OwnPtr<PassManager>, static_cast<UnderlyingType<Interpreter::OptimizationLevel>>(Interpreter::OptimizationLevel::__Count)> Interpreter::s_optimization_pipelines {};
+
+Bytecode::PassManager& Interpreter::optimization_pipeline(Interpreter::OptimizationLevel level)
+{
+    auto underlying_level = to_underlying(level);
+    VERIFY(underlying_level <= to_underlying(Interpreter::OptimizationLevel::__Count));
+    auto& entry = s_optimization_pipelines[underlying_level];
+
+    if (entry)
+        return *entry;
+
+    auto pm = make<PassManager>();
+    if (level == OptimizationLevel::Default) {
+        pm->add<Passes::GenerateCFG>();
+        pm->add<Passes::UnifySameBlocks>();
+        pm->add<Passes::GenerateCFG>();
+        pm->add<Passes::MergeBlocks>();
+        pm->add<Passes::GenerateCFG>();
+        pm->add<Passes::UnifySameBlocks>();
+        pm->add<Passes::GenerateCFG>();
+        pm->add<Passes::MergeBlocks>();
+        pm->add<Passes::GenerateCFG>();
+        pm->add<Passes::PlaceBlocks>();
+    } else {
+        VERIFY_NOT_REACHED();
+    }
+
+    auto& passes = *pm;
+    entry = move(pm);
+
+    return passes;
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Bytecode/Interpreter.h b/Userland/Libraries/LibJS/Bytecode/Interpreter.h
index 26b2dc9078..0dda59a99b 100644
--- a/Userland/Libraries/LibJS/Bytecode/Interpreter.h
+++ b/Userland/Libraries/LibJS/Bytecode/Interpreter.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "Generator.h"
+#include "PassManager.h"
 #include <LibJS/Bytecode/Label.h>
 #include <LibJS/Bytecode/Register.h>
 #include <LibJS/Forward.h>
@@ -60,9 +61,17 @@ public:
 
     Executable const& current_executable() { return *m_current_executable; }
 
+    enum class OptimizationLevel {
+        Default,
+        __Count,
+    };
+    static Bytecode::PassManager& optimization_pipeline(OptimizationLevel = OptimizationLevel::Default);
+
 private:
     RegisterWindow& registers() { return m_register_windows.last(); }
 
+    static AK::Array<OwnPtr<PassManager>, static_cast<UnderlyingType<Interpreter::OptimizationLevel>>(Interpreter::OptimizationLevel::__Count)> s_optimization_pipelines;
+
     VM& m_vm;
     GlobalObject& m_global_object;
     NonnullOwnPtrVector<RegisterWindow> m_register_windows;
diff --git a/Userland/Libraries/LibJS/Bytecode/Label.h b/Userland/Libraries/LibJS/Bytecode/Label.h
index 8174463f6e..b1634b1d0d 100644
--- a/Userland/Libraries/LibJS/Bytecode/Label.h
+++ b/Userland/Libraries/LibJS/Bytecode/Label.h
@@ -14,14 +14,14 @@ namespace JS::Bytecode {
 class Label {
 public:
     explicit Label(BasicBlock const& block)
-        : m_block(block)
+        : m_block(&block)
     {
     }
 
-    auto& block() const { return m_block; }
+    auto& block() const { return *m_block; }
 
 private:
-    BasicBlock const& m_block;
+    BasicBlock const* m_block { nullptr };
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Bytecode/Op.cpp b/Userland/Libraries/LibJS/Bytecode/Op.cpp
index 676267e4d2..69744b6c22 100644
--- a/Userland/Libraries/LibJS/Bytecode/Op.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Op.cpp
@@ -165,6 +165,14 @@ void Jump::execute_impl(Bytecode::Interpreter& interpreter) const
     interpreter.jump(*m_true_target);
 }
 
+void Jump::replace_references_impl(BasicBlock const& from, BasicBlock const& to)
+{
+    if (m_true_target.has_value() && &m_true_target->block() == &from)
+        m_true_target = Label { to };
+    if (m_false_target.has_value() && &m_false_target->block() == &from)
+        m_false_target = Label { to };
+}
+
 void JumpConditional::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     VERIFY(m_true_target.has_value());
@@ -261,6 +269,16 @@ void EnterUnwindContext::execute_impl(Bytecode::Interpreter& interpreter) const
     interpreter.jump(m_entry_point);
 }
 
+void EnterUnwindContext::replace_references_impl(BasicBlock const& from, BasicBlock const& to)
+{
+    if (&m_entry_point.block() == &from)
+        m_entry_point = Label { to };
+    if (m_handler_target.has_value() && &m_handler_target->block() == &from)
+        m_handler_target = Label { to };
+    if (m_finalizer_target.has_value() && &m_finalizer_target->block() == &from)
+        m_finalizer_target = Label { to };
+}
+
 void LeaveUnwindContext::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     interpreter.leave_unwind_context();
@@ -271,6 +289,12 @@ void ContinuePendingUnwind::execute_impl(Bytecode::Interpreter& interpreter) con
     interpreter.continue_pending_unwind(m_resume_target);
 }
 
+void ContinuePendingUnwind::replace_references_impl(BasicBlock const& from, BasicBlock const& to)
+{
+    if (&m_resume_target.block() == &from)
+        m_resume_target = Label { to };
+}
+
 void PushLexicalEnvironment::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     HashMap<FlyString, Variable> resolved_variables;
@@ -292,6 +316,12 @@ void Yield::execute_impl(Bytecode::Interpreter& interpreter) const
     interpreter.do_return(object);
 }
 
+void Yield::replace_references_impl(BasicBlock const& from, BasicBlock const& to)
+{
+    if (m_continuation_label.has_value() && &m_continuation_label->block() == &from)
+        m_continuation_label = Label { to };
+}
+
 void GetByValue::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     if (auto* object = interpreter.reg(m_base).to_object(interpreter.global_object())) {
diff --git a/Userland/Libraries/LibJS/Bytecode/Op.h b/Userland/Libraries/LibJS/Bytecode/Op.h
index 0ca7ad91ab..653b9d1889 100644
--- a/Userland/Libraries/LibJS/Bytecode/Op.h
+++ b/Userland/Libraries/LibJS/Bytecode/Op.h
@@ -29,6 +29,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_src;
@@ -44,6 +45,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Value m_value;
@@ -59,6 +61,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_dst;
@@ -88,20 +91,21 @@ private:
     O(RightShift, right_shift)                \
     O(UnsignedRightShift, unsigned_right_shift)
 
-#define JS_DECLARE_COMMON_BINARY_OP(OpTitleCase, op_snake_case)   \
-    class OpTitleCase final : public Instruction {                \
-    public:                                                       \
-        explicit OpTitleCase(Register lhs_reg)                    \
-            : Instruction(Type::OpTitleCase)                      \
-            , m_lhs_reg(lhs_reg)                                  \
-        {                                                         \
-        }                                                         \
-                                                                  \
-        void execute_impl(Bytecode::Interpreter&) const;          \
-        String to_string_impl(Bytecode::Executable const&) const; \
-                                                                  \
-    private:                                                      \
-        Register m_lhs_reg;                                       \
+#define JS_DECLARE_COMMON_BINARY_OP(OpTitleCase, op_snake_case)                \
+    class OpTitleCase final : public Instruction {                             \
+    public:                                                                    \
+        explicit OpTitleCase(Register lhs_reg)                                 \
+            : Instruction(Type::OpTitleCase)                                   \
+            , m_lhs_reg(lhs_reg)                                               \
+        {                                                                      \
+        }                                                                      \
+                                                                               \
+        void execute_impl(Bytecode::Interpreter&) const;                       \
+        String to_string_impl(Bytecode::Executable const&) const;              \
+        void replace_references_impl(BasicBlock const&, BasicBlock const&) { } \
+                                                                               \
+    private:                                                                   \
+        Register m_lhs_reg;                                                    \
     };
 
 JS_ENUMERATE_COMMON_BINARY_OPS(JS_DECLARE_COMMON_BINARY_OP)
@@ -114,16 +118,17 @@ JS_ENUMERATE_COMMON_BINARY_OPS(JS_DECLARE_COMMON_BINARY_OP)
     O(UnaryMinus, unary_minus)           \
     O(Typeof, typeof_)
 
-#define JS_DECLARE_COMMON_UNARY_OP(OpTitleCase, op_snake_case)    \
-    class OpTitleCase final : public Instruction {                \
-    public:                                                       \
-        OpTitleCase()                                             \
-            : Instruction(Type::OpTitleCase)                      \
-        {                                                         \
-        }                                                         \
-                                                                  \
-        void execute_impl(Bytecode::Interpreter&) const;          \
-        String to_string_impl(Bytecode::Executable const&) const; \
+#define JS_DECLARE_COMMON_UNARY_OP(OpTitleCase, op_snake_case)                 \
+    class OpTitleCase final : public Instruction {                             \
+    public:                                                                    \
+        OpTitleCase()                                                          \
+            : Instruction(Type::OpTitleCase)                                   \
+        {                                                                      \
+        }                                                                      \
+                                                                               \
+        void execute_impl(Bytecode::Interpreter&) const;                       \
+        String to_string_impl(Bytecode::Executable const&) const;              \
+        void replace_references_impl(BasicBlock const&, BasicBlock const&) { } \
     };
 
 JS_ENUMERATE_COMMON_UNARY_OPS(JS_DECLARE_COMMON_UNARY_OP)
@@ -139,6 +144,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     StringTableIndex m_string;
@@ -153,6 +159,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class NewBigInt final : public Instruction {
@@ -165,6 +172,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Crypto::SignedBigInteger m_bigint;
@@ -183,8 +191,12 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
-    size_t length_impl() const { return sizeof(*this) + sizeof(Register) * m_element_count; }
+    size_t length_impl() const
+    {
+        return sizeof(*this) + sizeof(Register) * m_element_count;
+    }
 
 private:
     size_t m_element_count { 0 };
@@ -201,6 +213,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_lhs;
@@ -216,6 +229,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     StringTableIndex m_identifier;
@@ -231,6 +245,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     StringTableIndex m_identifier;
@@ -246,6 +261,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     StringTableIndex m_property;
@@ -262,6 +278,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_base;
@@ -278,6 +295,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_base;
@@ -294,6 +312,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     Register m_base;
@@ -326,6 +345,10 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&);
+
+    auto& true_target() const { return m_true_target; }
+    auto& false_target() const { return m_false_target; }
 
 protected:
     Optional<Label> m_true_target;
@@ -375,8 +398,12 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
-    size_t length_impl() const { return sizeof(*this) + sizeof(Register) * m_argument_count; }
+    size_t length_impl() const
+    {
+        return sizeof(*this) + sizeof(Register) * m_argument_count;
+    }
 
 private:
     Register m_callee;
@@ -396,6 +423,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     FunctionNode const& m_function_node;
@@ -412,6 +440,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class Increment final : public Instruction {
@@ -423,6 +452,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class Decrement final : public Instruction {
@@ -434,6 +464,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class Throw final : public Instruction {
@@ -447,6 +478,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class EnterUnwindContext final : public Instruction {
@@ -463,6 +495,11 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&);
+
+    auto& entry_point() const { return m_entry_point; }
+    auto& handler_target() const { return m_handler_target; }
+    auto& finalizer_target() const { return m_finalizer_target; }
 
 private:
     Label m_entry_point;
@@ -479,6 +516,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 };
 
 class ContinuePendingUnwind final : public Instruction {
@@ -493,6 +531,9 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&);
+
+    auto& resume_target() const { return m_resume_target; }
 
 private:
     Label m_resume_target;
@@ -515,6 +556,9 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&);
+
+    auto& continuation() const { return m_continuation_label; }
 
 private:
     Optional<Label> m_continuation_label;
@@ -529,6 +573,7 @@ public:
     }
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     HashMap<u32, Variable> m_variables;
@@ -544,6 +589,7 @@ public:
 
     void execute_impl(Bytecode::Interpreter&) const;
     String to_string_impl(Bytecode::Executable const&) const;
+    void replace_references_impl(BasicBlock const&, BasicBlock const&) { }
 
 private:
     size_t m_index { 0 };
@@ -568,6 +614,21 @@ ALWAYS_INLINE void Instruction::execute(Bytecode::Interpreter& interpreter) cons
 #undef __BYTECODE_OP
 }
 
+ALWAYS_INLINE void Instruction::replace_references(BasicBlock const& from, BasicBlock const& to)
+{
+#define __BYTECODE_OP(op)       \
+    case Instruction::Type::op: \
+        return static_cast<Bytecode::Op::op&>(*this).replace_references_impl(from, to);
+
+    switch (type()) {
+        ENUMERATE_BYTECODE_OPS(__BYTECODE_OP)
+    default:
+        VERIFY_NOT_REACHED();
+    }
+
+#undef __BYTECODE_OP
+}
+
 ALWAYS_INLINE size_t Instruction::length() const
 {
     if (type() == Type::Call)
@@ -587,4 +648,18 @@ ALWAYS_INLINE size_t Instruction::length() const
 #undef __BYTECODE_OP
 }
 
+ALWAYS_INLINE bool Instruction::is_terminator() const
+{
+#define __BYTECODE_OP(op) \
+    case Type::op:        \
+        return Op::op::IsTerminator;
+
+    switch (type()) {
+        ENUMERATE_BYTECODE_OPS(__BYTECODE_OP)
+    default:
+        VERIFY_NOT_REACHED();
+    }
+#undef __BYTECODE_OP
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Bytecode/Pass/DumpCFG.cpp b/Userland/Libraries/LibJS/Bytecode/Pass/DumpCFG.cpp
new file mode 100644
index 0000000000..2d41134cfe
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/Pass/DumpCFG.cpp
@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/PassManager.h>
+#include <stdio.h>
+
+namespace JS::Bytecode::Passes {
+
+void DumpCFG::perform(PassPipelineExecutable& executable)
+{
+    started();
+
+    VERIFY(executable.cfg.has_value());
+    outln(m_file, "CFG Dump for {} basic blocks:", executable.executable.basic_blocks.size());
+    for (auto& entry : executable.cfg.value()) {
+        for (auto& value : entry.value)
+            outln(m_file, "{} -> {}", entry.key->name(), value->name());
+    }
+    outln(m_file);
+
+    finished();
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp b/Userland/Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp
new file mode 100644
index 0000000000..167e3c6052
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/Pass/GenerateCFG.cpp
@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/PassManager.h>
+
+namespace JS::Bytecode::Passes {
+
+void GenerateCFG::perform(PassPipelineExecutable& executable)
+{
+    started();
+
+    executable.cfg = HashMap<BasicBlock const*, HashTable<BasicBlock const*>> {};
+    executable.inverted_cfg = HashMap<BasicBlock const*, HashTable<BasicBlock const*>> {};
+    executable.exported_blocks = HashTable<BasicBlock const*> {};
+    Vector<InstructionStreamIterator> iterators;
+    Vector<BasicBlock const&> entered_blocks;
+    HashTable<BasicBlock const*> seen_blocks;
+
+    auto enter_label = [&](auto const& label, auto& entering_block, bool exported = false) {
+        auto& entry = executable.cfg->ensure(&entering_block);
+        entry.set(&label->block());
+        auto& inverse_entry = executable.inverted_cfg->ensure(&label->block());
+        inverse_entry.set(&entering_block);
+
+        if (exported)
+            executable.exported_blocks->set(&label->block());
+
+        if (!seen_blocks.contains(&label->block())) {
+            seen_blocks.set(&label->block());
+            entered_blocks.append(label->block());
+            iterators.empend(label->block().instruction_stream());
+        }
+    };
+
+    seen_blocks.set(&executable.executable.basic_blocks.first());
+    entered_blocks.append(executable.executable.basic_blocks.first());
+    iterators.empend(executable.executable.basic_blocks.first().instruction_stream());
+
+    while (!entered_blocks.is_empty()) {
+        if (iterators.last().at_end()) {
+            entered_blocks.take_last();
+            iterators.take_last();
+            continue;
+        }
+        auto& instruction = *iterators.last();
+        ++iterators.last();
+        if (!instruction.is_terminator())
+            continue;
+
+        auto& current_block = entered_blocks.last();
+
+        if (instruction.type() == Instruction::Type::Jump) {
+            auto& true_target = static_cast<Op::Jump const&>(instruction).true_target();
+            enter_label(true_target, current_block);
+            continue;
+        }
+
+        if (instruction.type() == Instruction::Type::JumpConditional || instruction.type() == Instruction::Type::JumpNullish) {
+            auto& true_target = static_cast<Op::Jump const&>(instruction).true_target();
+            enter_label(true_target, current_block);
+            auto& false_target = static_cast<Op::Jump const&>(instruction).false_target();
+            enter_label(false_target, current_block);
+            continue;
+        }
+
+        if (instruction.type() == Instruction::Type::Yield) {
+            auto& continuation = static_cast<Op::Yield const&>(instruction).continuation();
+            if (continuation.has_value())
+                enter_label(continuation, current_block, true);
+            continue;
+        }
+
+        if (instruction.type() == Instruction::Type::EnterUnwindContext) {
+            auto& entry_point = static_cast<Op::EnterUnwindContext const&>(instruction).entry_point();
+            auto& handler_target = static_cast<Op::EnterUnwindContext const&>(instruction).handler_target();
+            auto& finalizer_target = static_cast<Op::EnterUnwindContext const&>(instruction).finalizer_target();
+            enter_label(&entry_point, current_block);
+            if (handler_target.has_value())
+                enter_label(handler_target, current_block);
+            if (finalizer_target.has_value())
+                enter_label(finalizer_target, current_block);
+            continue;
+        }
+
+        if (instruction.type() == Instruction::Type::ContinuePendingUnwind) {
+            auto& resume_target = static_cast<Op::ContinuePendingUnwind const&>(instruction).resume_target();
+            enter_label(&resume_target, current_block);
+            continue;
+        }
+
+        // Otherwise, pop the current block off, it doesn't jump anywhere.
+        iterators.take_last();
+        entered_blocks.take_last();
+    }
+
+    finished();
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Bytecode/Pass/MergeBlocks.cpp b/Userland/Libraries/LibJS/Bytecode/Pass/MergeBlocks.cpp
new file mode 100644
index 0000000000..a3b00857b9
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/Pass/MergeBlocks.cpp
@@ -0,0 +1,165 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/PassManager.h>
+
+namespace JS::Bytecode::Passes {
+
+void MergeBlocks::perform(PassPipelineExecutable& executable)
+{
+    started();
+
+    VERIFY(executable.cfg.has_value());
+    VERIFY(executable.inverted_cfg.has_value());
+    auto cfg = executable.cfg.release_value();
+    auto inverted_cfg = executable.inverted_cfg.release_value();
+
+    // Figure out which blocks can be merged
+    HashTable<BasicBlock const*> blocks_to_merge;
+    HashMap<BasicBlock const*, BasicBlock const*> blocks_to_replace;
+    Vector<BasicBlock const*> blocks_to_remove;
+    Vector<size_t> boundaries;
+
+    for (auto& entry : cfg) {
+        if (entry.value.size() != 1)
+            continue;
+
+        if (executable.exported_blocks->contains(*entry.value.begin()))
+            continue;
+
+        {
+            InstructionStreamIterator it { entry.key->instruction_stream() };
+            auto& first_instruction = *it;
+            if (first_instruction.is_terminator()) {
+                if (first_instruction.type() == Instruction::Type::Jump) {
+                    auto replacing_block = &static_cast<Op::Jump const&>(first_instruction).true_target()->block();
+                    if (replacing_block != entry.key)
+                        blocks_to_replace.set(entry.key, replacing_block);
+                    continue;
+                }
+            }
+        }
+
+        if (auto cfg_entry = inverted_cfg.get(*entry.value.begin()); cfg_entry.has_value()) {
+            auto& predecssor_entry = *cfg_entry;
+            if (predecssor_entry.size() != 1)
+                continue;
+        }
+
+        // The two blocks are safe to merge.
+        blocks_to_merge.set(entry.key);
+    }
+
+    for (auto& entry : blocks_to_replace) {
+        auto replacement = entry.value;
+        for (;;) {
+            auto lookup = blocks_to_replace.get(replacement);
+            if (!lookup.has_value())
+                break;
+            if (replacement == *lookup)
+                break;
+            replacement = *lookup;
+        }
+        entry.value = replacement;
+    }
+
+    auto replace_blocks = [&](auto& blocks, auto& replacement) {
+        Optional<size_t> first_successor_position;
+        for (auto& entry : blocks) {
+            blocks_to_remove.append(entry);
+            auto it = executable.executable.basic_blocks.find_if([entry](auto& block) { return entry == block; });
+            VERIFY(!it.is_end());
+            if (!first_successor_position.has_value())
+                first_successor_position = it.index();
+        }
+        for (auto& block : executable.executable.basic_blocks) {
+            InstructionStreamIterator it { block.instruction_stream() };
+            while (!it.at_end()) {
+                auto& instruction = *it;
+                ++it;
+                for (auto& entry : blocks)
+                    const_cast<Instruction&>(instruction).replace_references(*entry, replacement);
+            }
+        }
+        return first_successor_position;
+    };
+
+    for (auto& entry : blocks_to_replace) {
+        AK::Array candidates { entry.key };
+        (void)replace_blocks(candidates, *entry.value);
+    }
+
+    while (!blocks_to_merge.is_empty()) {
+        auto it = blocks_to_merge.begin();
+        auto current_block = *it;
+        blocks_to_merge.remove(it);
+        Vector<BasicBlock const*> successors { current_block };
+        for (;;) {
+            auto last = successors.last();
+            auto entry = cfg.get(last);
+            if (!entry.has_value())
+                break;
+            auto& successor = *entry->begin();
+            successors.append(successor);
+            auto it = blocks_to_merge.find(successor);
+            if (it == blocks_to_merge.end())
+                break;
+            blocks_to_merge.remove(it);
+        }
+
+        auto blocks_to_merge_copy = blocks_to_merge;
+        for (auto& last : blocks_to_merge) {
+            auto entry = cfg.get(last);
+            if (!entry.has_value())
+                continue;
+            auto successor = *entry->begin();
+            if (auto it = successors.find(successor); !it.is_end()) {
+                successors.insert(it.index(), last);
+                blocks_to_merge_copy.remove(last);
+            }
+        }
+
+        blocks_to_merge = move(blocks_to_merge_copy);
+
+        size_t size = 0;
+        StringBuilder builder;
+        builder.append("merge");
+        for (auto& entry : successors) {
+            size += entry->size();
+            builder.append('.');
+            builder.append(entry->name());
+        }
+
+        auto new_block = BasicBlock::create(builder.build(), size);
+        auto& block = *new_block;
+
+        size_t last_successor_index = successors.size() - 1;
+        for (size_t i = 0; i < successors.size(); ++i) {
+            auto& entry = successors[i];
+            InstructionStreamIterator it { entry->instruction_stream() };
+            size_t copy_end = 0;
+            while (!it.at_end()) {
+                auto& instruction = *it;
+                ++it;
+                if (instruction.is_terminator() && last_successor_index != i)
+                    break;
+                copy_end = it.offset();
+            }
+            __builtin_memcpy(block.next_slot(), entry->instruction_stream().data(), copy_end);
+            block.grow(copy_end);
+        }
+
+        auto first_successor_position = replace_blocks(successors, *new_block);
+        VERIFY(first_successor_position.has_value());
+        executable.executable.basic_blocks.insert(*first_successor_position, move(new_block));
+    }
+
+    executable.executable.basic_blocks.remove_all_matching([&blocks_to_remove](auto& candidate) { return blocks_to_remove.contains_slow(candidate.ptr()); });
+
+    finished();
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Bytecode/Pass/PlaceBlocks.cpp b/Userland/Libraries/LibJS/Bytecode/Pass/PlaceBlocks.cpp
new file mode 100644
index 0000000000..4a320ac470
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/Pass/PlaceBlocks.cpp
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/PassManager.h>
+
+namespace JS::Bytecode::Passes {
+
+void PlaceBlocks::perform(PassPipelineExecutable& executable)
+{
+    started();
+
+    VERIFY(executable.cfg.has_value());
+    auto cfg = executable.cfg.release_value();
+
+    Vector<BasicBlock&> replaced_blocks;
+    HashTable<BasicBlock const*> reachable_blocks;
+
+    // Visit the blocks in CFG order
+    AK::Function<void(BasicBlock const*)> visit = [&](auto* block) {
+        if (reachable_blocks.contains(block))
+            return;
+
+        reachable_blocks.set(block);
+        replaced_blocks.append(*const_cast<BasicBlock*>(block));
+
+        for (auto& entry : cfg.get(block).value_or({}))
+            visit(entry);
+    };
+
+    // Make sure to visit the entry block first
+    visit(&executable.executable.basic_blocks.first());
+
+    for (auto& entry : cfg)
+        visit(entry.key);
+
+    // Put the unreferenced blocks back in at the end
+    for (auto& entry : static_cast<Vector<NonnullOwnPtr<BasicBlock>>&>(executable.executable.basic_blocks)) {
+        if (reachable_blocks.contains(entry.ptr()))
+            (void)entry.leak_ptr();
+        else
+            replaced_blocks.append(*entry.leak_ptr()); // Don't try to do DCE here.
+    }
+
+    executable.executable.basic_blocks.clear();
+    for (auto& block : replaced_blocks)
+        executable.executable.basic_blocks.append(adopt_own(block));
+
+    finished();
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Bytecode/Pass/UnifySameBlocks.cpp b/Userland/Libraries/LibJS/Bytecode/Pass/UnifySameBlocks.cpp
new file mode 100644
index 0000000000..70be9244e2
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/Pass/UnifySameBlocks.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Bytecode/PassManager.h>
+#include <string.h>
+
+namespace JS::Bytecode::Passes {
+
+void UnifySameBlocks::perform(PassPipelineExecutable& executable)
+{
+    started();
+
+    VERIFY(executable.cfg.has_value());
+    VERIFY(executable.inverted_cfg.has_value());
+    auto cfg = executable.cfg.release_value();
+    auto inverted_cfg = executable.inverted_cfg.release_value();
+
+    HashMap<BasicBlock const*, BasicBlock const*> equal_blocks;
+
+    for (size_t i = 0; i < executable.executable.basic_blocks.size(); ++i) {
+        auto& block = executable.executable.basic_blocks[i];
+        auto block_bytes = block.instruction_stream();
+        for (auto& candidate_block : executable.executable.basic_blocks.span().slice(i + 1)) {
+            // FIXME: This can probably be relaxed a bit...
+            if (candidate_block->size() != block.size())
+                continue;
+
+            auto candidate_bytes = candidate_block->instruction_stream();
+            if (memcmp(candidate_bytes.data(), block_bytes.data(), candidate_block->size()) == 0)
+                equal_blocks.set(&*candidate_block, &block);
+        }
+    }
+
+    auto replace_blocks = [&](auto& match, auto& replacement) {
+        Optional<size_t> first_successor_position;
+        auto it = executable.executable.basic_blocks.find_if([match](auto& block) { return match == block; });
+        VERIFY(!it.is_end());
+        executable.executable.basic_blocks.remove(it.index());
+        if (!first_successor_position.has_value())
+            first_successor_position = it.index();
+
+        for (auto& block : executable.executable.basic_blocks) {
+            InstructionStreamIterator it { block.instruction_stream() };
+            while (!it.at_end()) {
+                auto& instruction = *it;
+                ++it;
+                const_cast<Instruction&>(instruction).replace_references(*match, replacement);
+            }
+        }
+        return first_successor_position;
+    };
+
+    for (auto& entry : equal_blocks)
+        (void)replace_blocks(entry.key, *entry.value);
+
+    finished();
+}
+
+}
diff --git a/Userland/Libraries/LibJS/Bytecode/PassManager.h b/Userland/Libraries/LibJS/Bytecode/PassManager.h
new file mode 100644
index 0000000000..b4a44da5c5
--- /dev/null
+++ b/Userland/Libraries/LibJS/Bytecode/PassManager.h
@@ -0,0 +1,141 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Bytecode/BasicBlock.h>
+#include <LibJS/Bytecode/Generator.h>
+#include <sys/time.h>
+#include <time.h>
+
+namespace JS::Bytecode {
+
+struct PassPipelineExecutable {
+    Executable& executable;
+    Optional<HashMap<BasicBlock const*, HashTable<BasicBlock const*>>> cfg {};
+    Optional<HashMap<BasicBlock const*, HashTable<BasicBlock const*>>> inverted_cfg {};
+    Optional<HashTable<BasicBlock const*>> exported_blocks {};
+};
+
+class Pass {
+public:
+    Pass() = default;
+    virtual ~Pass() = default;
+
+    virtual void perform(PassPipelineExecutable&) = 0;
+    void started()
+    {
+        gettimeofday(&m_start_time, nullptr);
+    }
+    void finished()
+    {
+        struct timeval end_time {
+            0, 0
+        };
+        gettimeofday(&end_time, nullptr);
+        time_t interval_s = end_time.tv_sec - m_start_time.tv_sec;
+        suseconds_t interval_us = end_time.tv_usec;
+        if (interval_us < m_start_time.tv_usec) {
+            interval_s -= 1;
+            interval_us += 1000000;
+        }
+        interval_us -= m_start_time.tv_usec;
+        m_time_difference = interval_s * 1000000 + interval_us;
+    }
+
+    u64 elapsed() const { return m_time_difference; }
+
+protected:
+    struct timeval m_start_time {
+        0, 0
+    };
+    u64 m_time_difference { 0 };
+};
+
+class PassManager : public Pass {
+public:
+    PassManager() = default;
+    ~PassManager() override = default;
+
+    void add(NonnullOwnPtr<Pass> pass) { m_passes.append(move(pass)); }
+
+    template<typename PassT, typename... Args>
+    void add(Args&&... args) { m_passes.append(make<PassT>(forward<Args>(args)...)); }
+
+    void perform(Executable& executable)
+    {
+        PassPipelineExecutable pipeline_executable { executable };
+        perform(pipeline_executable);
+    }
+
+    virtual void perform(PassPipelineExecutable& executable) override
+    {
+        started();
+        for (auto& pass : m_passes)
+            pass.perform(executable);
+        finished();
+    }
+
+private:
+    NonnullOwnPtrVector<Pass> m_passes;
+};
+
+namespace Passes {
+
+class GenerateCFG : public Pass {
+public:
+    GenerateCFG() = default;
+    ~GenerateCFG() override = default;
+
+private:
+    virtual void perform(PassPipelineExecutable&) override;
+};
+
+class MergeBlocks : public Pass {
+public:
+    MergeBlocks() = default;
+    ~MergeBlocks() override = default;
+
+private:
+    virtual void perform(PassPipelineExecutable&) override;
+};
+
+class PlaceBlocks : public Pass {
+public:
+    PlaceBlocks() = default;
+    ~PlaceBlocks() override = default;
+
+private:
+    virtual void perform(PassPipelineExecutable&) override;
+};
+
+class UnifySameBlocks : public Pass {
+public:
+    UnifySameBlocks() = default;
+    ~UnifySameBlocks() override = default;
+
+private:
+    virtual void perform(PassPipelineExecutable&) override;
+};
+
+class DumpCFG : public Pass {
+public:
+    DumpCFG(FILE* file)
+        : m_file(file)
+    {
+    }
+
+    ~DumpCFG() override = default;
+
+private:
+    virtual void perform(PassPipelineExecutable&) override;
+
+    FILE* m_file { nullptr };
+};
+
+}
+
+}
diff --git a/Userland/Libraries/LibJS/CMakeLists.txt b/Userland/Libraries/LibJS/CMakeLists.txt
index 7838999228..a7369a2440 100644
--- a/Userland/Libraries/LibJS/CMakeLists.txt
+++ b/Userland/Libraries/LibJS/CMakeLists.txt
@@ -6,6 +6,11 @@ set(SOURCES
     Bytecode/Instruction.cpp
     Bytecode/Interpreter.cpp
     Bytecode/Op.cpp
+    Bytecode/Pass/DumpCFG.cpp
+    Bytecode/Pass/GenerateCFG.cpp
+    Bytecode/Pass/MergeBlocks.cpp
+    Bytecode/Pass/PlaceBlocks.cpp
+    Bytecode/Pass/UnifySameBlocks.cpp
     Bytecode/StringTable.cpp
     Console.cpp
     Heap/CellAllocator.cpp
diff --git a/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp b/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
index 433e6cd807..f90304190b 100644
--- a/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp
@@ -10,6 +10,7 @@
 #include <LibJS/Bytecode/BasicBlock.h>
 #include <LibJS/Bytecode/Generator.h>
 #include <LibJS/Bytecode/Interpreter.h>
+#include <LibJS/Bytecode/PassManager.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Error.h>
@@ -159,7 +160,10 @@ Value ScriptFunction::execute_function_body()
         prepare_arguments();
         if (!m_bytecode_executable.has_value()) {
             m_bytecode_executable = Bytecode::Generator::generate(m_body, m_kind == FunctionKind::Generator);
+            auto& passes = JS::Bytecode::Interpreter::optimization_pipeline();
+            passes.perform(*m_bytecode_executable);
             if constexpr (JS_BYTECODE_DEBUG) {
+                dbgln("Optimisation passes took {}us", passes.elapsed());
                 dbgln("Compiled Bytecode::Block for function '{}':", m_name);
                 for (auto& block : m_bytecode_executable->basic_blocks)
                     block.dump(*m_bytecode_executable);
diff --git a/Userland/Utilities/js.cpp b/Userland/Utilities/js.cpp
index 1ad0d7f852..e7dafdd424 100644
--- a/Userland/Utilities/js.cpp
+++ b/Userland/Utilities/js.cpp
@@ -17,6 +17,7 @@
 #include <LibJS/Bytecode/BasicBlock.h>
 #include <LibJS/Bytecode/Generator.h>
 #include <LibJS/Bytecode/Interpreter.h>
+#include <LibJS/Bytecode/PassManager.h>
 #include <LibJS/Console.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Parser.h>
@@ -81,6 +82,7 @@ private:
 static bool s_dump_ast = false;
 static bool s_dump_bytecode = false;
 static bool s_run_bytecode = false;
+static bool s_opt_bytecode = false;
 static bool s_print_last_result = false;
 static RefPtr<Line::Editor> s_editor;
 static String s_history_path = String::formatted("{}/.js-history", Core::StandardPaths::home_directory());
@@ -558,6 +560,12 @@ static bool parse_and_run(JS::Interpreter& interpreter, const StringView& source
     } else {
         if (s_dump_bytecode || s_run_bytecode) {
             auto unit = JS::Bytecode::Generator::generate(*program);
+            if (s_opt_bytecode) {
+                auto& passes = JS::Bytecode::Interpreter::optimization_pipeline();
+                passes.perform(unit);
+                dbgln("Optimisation passes took {}us", passes.elapsed());
+            }
+
             if (s_dump_bytecode) {
                 for (auto& block : unit.basic_blocks)
                     block.dump(unit);
@@ -825,6 +833,7 @@ int main(int argc, char** argv)
     args_parser.add_option(s_dump_ast, "Dump the AST", "dump-ast", 'A');
     args_parser.add_option(s_dump_bytecode, "Dump the bytecode", "dump-bytecode", 'd');
     args_parser.add_option(s_run_bytecode, "Run the bytecode", "run-bytecode", 'b');
+    args_parser.add_option(s_opt_bytecode, "Optimize the bytecode", "optimize-bytecode", 'p');
     args_parser.add_option(s_print_last_result, "Print last result", "print-last-result", 'l');
     args_parser.add_option(gc_on_every_allocation, "GC on every allocation", "gc-on-every-allocation", 'g');
     args_parser.add_option(disable_syntax_highlight, "Disable live syntax highlighting", "no-syntax-highlight", 's');
-- 
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