LibJS: Create static unwind mappings for BasicBlocks

This is currently only used in the bytecode dump to annotate to where
unwinds lead per block, but will be hooked up to the virtual machine in
the next commit.

Author: Hendiadyoin1

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -2308,6 +2308,7 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
 
     Optional<Bytecode::Label> handler_target;
     Optional<Bytecode::Label> finalizer_target;
+    Optional<Bytecode::Generator::UnwindContext> unwind_context;
 
     Bytecode::BasicBlock* next_block { nullptr };
 
@@ -2323,10 +2324,10 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
             generator.emit<Bytecode::Op::ContinuePendingUnwind>(next_target);
         }
         finalizer_target = Bytecode::Label { finalizer_block };
-    }
 
-    if (m_finalizer)
         generator.start_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
+        unwind_context.emplace(generator, finalizer_target);
+    }
     if (m_handler) {
         auto& handler_block = generator.make_block();
         generator.switch_to_basic_block(handler_block);
@@ -2374,6 +2375,7 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
                 generator.emit<Bytecode::Op::Jump>(*finalizer_target);
             } else {
                 VERIFY(!next_block);
+                VERIFY(!unwind_context.has_value());
                 next_block = &generator.make_block();
                 auto next_target = Bytecode::Label { *next_block };
                 generator.emit<Bytecode::Op::Jump>(next_target);
@@ -2382,6 +2384,11 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
     }
     if (m_finalizer)
         generator.end_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
+    if (m_handler) {
+        if (!m_finalizer)
+            unwind_context.emplace(generator, OptionalNone());
+        unwind_context->set_handler(handler_target.value());
+    }
 
     auto& target_block = generator.make_block();
     generator.switch_to_basic_block(saved_block);
@@ -2396,6 +2403,8 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
         if (m_finalizer) {
             generator.emit<Bytecode::Op::Jump>(*finalizer_target);
         } else {
+            VERIFY(unwind_context.has_value());
+            unwind_context.clear();
             if (!next_block)
                 next_block = &generator.make_block();
             generator.emit<Bytecode::Op::LeaveUnwindContext>();

Userland/Libraries/LibJS/Bytecode/BasicBlock.cpp

@@ -33,8 +33,18 @@ BasicBlock::~BasicBlock()
 void BasicBlock::dump(Bytecode::Executable const& executable) const
 {
     Bytecode::InstructionStreamIterator it(instruction_stream());
+
     if (!m_name.is_empty())
-        warnln("{}:", m_name);
+        warn("{}", m_name);
+    if (m_handler || m_finalizer) {
+        warn(" [");
+        if (m_handler)
+            warn(" Handler: {}", Label { *m_handler });
+        if (m_finalizer)
+            warn(" Finalizer: {}", Label { *m_finalizer });
+        warn(" ]");
+    }
+    warnln(":");
     while (!it.at_end()) {
         warnln("[{:4x}] {}", it.offset(), (*it).to_deprecated_string(executable));
         ++it;

Userland/Libraries/LibJS/Bytecode/BasicBlock.h

@@ -43,10 +43,18 @@ class BasicBlock {
 
     DeprecatedString const& name() const { return m_name; }
 
+    void set_handler(BasicBlock const& handler) { m_handler = &handler; }
+    void set_finalizer(BasicBlock const& finalizer) { m_finalizer = &finalizer; }
+
+    BasicBlock const* handler() const { return m_handler; }
+    BasicBlock const* finalizer() const { return m_finalizer; }
+
 private:
     explicit BasicBlock(DeprecatedString name);
 
     Vector<u8> m_buffer;
+    BasicBlock const* m_handler { nullptr };
+    BasicBlock const* m_finalizer { nullptr };
     DeprecatedString m_name;
     bool m_terminated { false };
 };

Userland/Libraries/LibJS/Bytecode/Executable.h

@@ -7,10 +7,12 @@
 #pragma once
 
 #include <AK/DeprecatedFlyString.h>
+#include <AK/HashMap.h>
 #include <AK/NonnullOwnPtr.h>
 #include <AK/OwnPtr.h>
 #include <AK/WeakPtr.h>
 #include <LibJS/Bytecode/IdentifierTable.h>
+#include <LibJS/Bytecode/Label.h>
 #include <LibJS/Bytecode/StringTable.h>
 #include <LibJS/Forward.h>
 #include <LibJS/JIT/NativeExecutable.h>
@@ -57,6 +59,7 @@ class Executable final : public RefCounted<Executable> {
     NonnullOwnPtr<StringTable> string_table;
     NonnullOwnPtr<IdentifierTable> identifier_table;
     NonnullOwnPtr<RegexTable> regex_table;
+
     NonnullRefPtr<SourceCode const> source_code;
     size_t number_of_registers { 0 };
     bool is_strict_mode { false };

Userland/Libraries/LibJS/Bytecode/Generator.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/TemporaryChange.h>
 #include <LibJS/AST.h>
 #include <LibJS/Bytecode/BasicBlock.h>
 #include <LibJS/Bytecode/Generator.h>
@@ -95,6 +96,20 @@ Generator::SourceLocationScope::~SourceLocationScope()
     m_generator.m_current_ast_node = m_previous_node;
 }
 
+Generator::UnwindContext::UnwindContext(Generator& generator, Optional<Label> finalizer)
+    : m_generator(generator)
+    , m_finalizer(finalizer)
+    , m_previous_context(m_generator.m_current_unwind_context)
+{
+    m_generator.m_current_unwind_context = this;
+}
+
+Generator::UnwindContext::~UnwindContext()
+{
+    VERIFY(m_generator.m_current_unwind_context == this);
+    m_generator.m_current_unwind_context = m_previous_context;
+}
+
 Label Generator::nearest_continuable_scope() const
 {
     return m_continuable_scopes.last().bytecode_target;
@@ -400,6 +415,7 @@ void Generator::emit_set_variable(JS::Identifier const& identifier, Bytecode::Op
 
 void Generator::generate_scoped_jump(JumpType type)
 {
+    TemporaryChange temp { m_current_unwind_context, m_current_unwind_context };
     bool last_was_finally = false;
     for (size_t i = m_boundaries.size(); i > 0; --i) {
         auto boundary = m_boundaries[i - 1];
@@ -418,14 +434,20 @@ void Generator::generate_scoped_jump(JumpType type)
             }
             break;
         case Unwind:
-            if (!last_was_finally)
+            VERIFY(last_was_finally || !m_current_unwind_context->finalizer().has_value());
+            if (!last_was_finally) {
+                VERIFY(m_current_unwind_context && m_current_unwind_context->handler().has_value());
                 emit<Bytecode::Op::LeaveUnwindContext>();
+                m_current_unwind_context = m_current_unwind_context->previous();
+            }
             last_was_finally = false;
             break;
         case LeaveLexicalEnvironment:
             emit<Bytecode::Op::LeaveLexicalEnvironment>();
             break;
         case ReturnToFinally: {
+            VERIFY(m_current_unwind_context->finalizer().has_value());
+            m_current_unwind_context = m_current_unwind_context->previous();
             auto jump_type_name = type == JumpType::Break ? "break"sv : "continue"sv;
             auto& block = make_block(DeprecatedString::formatted("{}.{}", current_block().name(), jump_type_name));
             emit<Op::ScheduleJump>(Label { block });
@@ -440,6 +462,7 @@ void Generator::generate_scoped_jump(JumpType type)
 
 void Generator::generate_labelled_jump(JumpType type, DeprecatedFlyString const& label)
 {
+    TemporaryChange temp { m_current_unwind_context, m_current_unwind_context };
     size_t current_boundary = m_boundaries.size();
     bool last_was_finally = false;
 
@@ -449,12 +472,18 @@ void Generator::generate_labelled_jump(JumpType type, DeprecatedFlyString const&
         for (; current_boundary > 0; --current_boundary) {
             auto boundary = m_boundaries[current_boundary - 1];
             if (boundary == BlockBoundaryType::Unwind) {
-                if (!last_was_finally)
+                VERIFY(last_was_finally || !m_current_unwind_context->finalizer().has_value());
+                if (!last_was_finally) {
+                    VERIFY(m_current_unwind_context && m_current_unwind_context->handler().has_value());
                     emit<Bytecode::Op::LeaveUnwindContext>();
+                    m_current_unwind_context = m_current_unwind_context->previous();
+                }
                 last_was_finally = false;
             } else if (boundary == BlockBoundaryType::LeaveLexicalEnvironment) {
                 emit<Bytecode::Op::LeaveLexicalEnvironment>();
             } else if (boundary == BlockBoundaryType::ReturnToFinally) {
+                VERIFY(m_current_unwind_context->finalizer().has_value());
+                m_current_unwind_context = m_current_unwind_context->previous();
                 auto jump_type_name = type == JumpType::Break ? "break"sv : "continue"sv;
                 auto& block = make_block(DeprecatedString::formatted("{}.{}", current_block().name(), jump_type_name));
                 emit<Op::ScheduleJump>(Label { block });

Userland/Libraries/LibJS/Bytecode/Generator.h

@@ -44,6 +44,24 @@ class Generator {
         ASTNode const* m_previous_node { nullptr };
     };
 
+    class UnwindContext {
+    public:
+        UnwindContext(Generator&, Optional<Label> finalizer);
+
+        UnwindContext const* previous() const { return m_previous_context; }
+        void set_handler(Label handler) { m_handler = handler; }
+        Optional<Label> handler() const { return m_handler; }
+        Optional<Label> finalizer() const { return m_finalizer; }
+
+        ~UnwindContext();
+
+    private:
+        Generator& m_generator;
+        Optional<Label> m_finalizer;
+        Optional<Label> m_handler {};
+        UnwindContext const* m_previous_context { nullptr };
+    };
+
     template<typename OpType, typename... Args>
     void emit(Args&&... args)
     {
@@ -114,7 +132,14 @@ class Generator {
     {
         if (name.is_empty())
             name = DeprecatedString::number(m_next_block++);
-        m_root_basic_blocks.append(BasicBlock::create(name));
+        auto block = BasicBlock::create(name);
+        if (auto const* context = m_current_unwind_context) {
+            if (context->handler().has_value())
+                block->set_handler(context->handler().value().block());
+            if (m_current_unwind_context->finalizer().has_value())
+                block->set_finalizer(context->finalizer().value().block());
+        }
+        m_root_basic_blocks.append(move(block));
         return *m_root_basic_blocks.last();
     }
 
@@ -228,6 +253,8 @@ class Generator {
 
     BasicBlock* m_current_basic_block { nullptr };
     ASTNode const* m_current_ast_node { nullptr };
+    UnwindContext const* m_current_unwind_context { nullptr };
+
     Vector<NonnullOwnPtr<BasicBlock>> m_root_basic_blocks;
     NonnullOwnPtr<StringTable> m_string_table;
     NonnullOwnPtr<IdentifierTable> m_identifier_table;