Custom stack for IVM. 2-3x faster.

src/alloy/backend/ivm/ivm_backend.cc

@@ -10,6 +10,7 @@
 #include <alloy/backend/ivm/ivm_backend.h>
 
 #include <alloy/backend/ivm/ivm_assembler.h>
+#include <alloy/backend/ivm/ivm_stack.h>
 #include <alloy/backend/ivm/tracing.h>
 
 using namespace alloy;
@@ -39,6 +40,15 @@ int IVMBackend::Initialize() {
   return result;
 }
 
+void* IVMBackend::AllocThreadData() {
+  return new IVMStack();
+}
+
+void IVMBackend::FreeThreadData(void* thread_data) {
+  auto stack = (IVMStack*)thread_data;
+  delete stack;
+}
+
 Assembler* IVMBackend::CreateAssembler() {
   return new IVMAssembler(this);
 }