LibJS: Stop worrying about Instruction destructors

By adding static_asserts to prove that all of our generated instruction
classes are trivially destructible, we can confidently remove the
destructor walk in BasicBlock and save ourselves some unnecessary work.

Author: awesomekling

Libraries/LibJS/Bytecode/BasicBlock.cpp

@@ -21,15 +21,7 @@ BasicBlock::BasicBlock(u32 index, String name)
 {
 }
 
-BasicBlock::~BasicBlock()
-{
-    Bytecode::InstructionStreamIterator it(instruction_stream());
-    while (!it.at_end()) {
-        auto& to_destroy = (*it);
-        ++it;
-        Instruction::destroy(const_cast<Instruction&>(to_destroy));
-    }
-}
+BasicBlock::~BasicBlock() = default;
 
 void BasicBlock::grow(size_t additional_size)
 {

Libraries/LibJS/Bytecode/Instruction.cpp

@@ -10,22 +10,6 @@
 
 namespace JS::Bytecode {
 
-void Instruction::destroy(Instruction& instruction)
-{
-#define __BYTECODE_OP(op)                        \
-    case Type::op:                               \
-        static_cast<Op::op&>(instruction).~op(); \
-        return;
-
-    switch (instruction.type()) {
-        ENUMERATE_BYTECODE_OPS(__BYTECODE_OP)
-    default:
-        VERIFY_NOT_REACHED();
-    }
-
-#undef __BYTECODE_OP
-}
-
 void Instruction::visit_labels(Function<void(JS::Bytecode::Label&)> visitor)
 {
 #define __BYTECODE_OP(op)                                             \

Libraries/LibJS/Bytecode/Instruction.h

@@ -8,7 +8,6 @@
 
 #include <AK/Forward.h>
 #include <AK/Function.h>
-#include <AK/Span.h>
 #include <LibJS/Bytecode/Executable.h>
 #include <LibJS/Bytecode/OpCodes.h>
 #include <LibJS/Forward.h>
@@ -85,7 +84,6 @@ class alignas(void*) Instruction {
     ByteString to_byte_string(Bytecode::Executable const&) const;
     void visit_labels(Function<void(Label&)> visitor);
     void visit_operands(Function<void(Operand&)> visitor);
-    static void destroy(Instruction&);
 
     Strict strict() const { return m_strict; }
     void set_strict(Strict strict) { m_strict = strict; }

Meta/generate-libjs-bytecode-def-derived.py

@@ -322,6 +322,7 @@ def generate_class(op: OpDef) -> str:
                 lines.append(f"    {f.type} {f.name};")
 
     lines.append("};")
+    lines.append(f"static_assert(IsTriviallyDestructible<{op.name}>);")
     return "\n".join(lines)