v8: avoid unnecessary log level checks. (#146)

It's mostly a pedantic change, but it slightly improves performance
in microbenchmarks.

Benchmark                                                       Diff
--------------------------------------------------------------------
WasmSpeedTest_empty                                          -0.0891
WasmSpeedTest_get_current_time                               -0.0424
WasmSpeedTest_small_string                                   -0.0507
WasmSpeedTest_small_string1000                               -0.0118
WasmSpeedTest_small_string_check_compiler                    -0.0556
WasmSpeedTest_small_string_check_compiler1000                +0.0041
WasmSpeedTest_large_string                                   -0.0322
WasmSpeedTest_large_string1000                               -0.0311
WasmSpeedTest_get_property                                   -0.0173
WasmSpeedTest_grpc_service                                   -0.0558
WasmSpeedTest_grpc_service1000                               -0.0021
WasmSpeedTest_modify_metadata                                +0.0410
WasmSpeedTest_modify_metadata1000                            -0.0298
WasmSpeedTest_json_serialize                                 +0.0009
WasmSpeedTest_json_deserialize                               +0.0028
WasmSpeedTest_json_deserialize_empty                         -0.0028
WasmSpeedTest_convert_to_filter_state                        -0.0172

Signed-off-by: Piotr Sikora <[email protected]>

Author: PiotrSikora

src/v8/v8.cc

@@ -649,15 +649,16 @@ void V8::registerHostFunctionImpl(std::string_view module_name, std::string_view
       store_.get(), type.get(),
       [](void *data, const wasm::Val params[], wasm::Val[]) -> wasm::own<wasm::Trap> {
         auto func_data = reinterpret_cast<FuncData *>(data);
-        if (func_data->vm_->cmpLogLevel(LogLevel::trace)) {
+        const bool log = func_data->vm_->cmpLogLevel(LogLevel::trace);
+        if (log) {
           func_data->vm_->integration()->trace("[vm->host] " + func_data->name_ + "(" +
                                                printValues(params, sizeof...(Args)) + ")");
         }
         auto args_tuple = convertValTypesToArgsTuple<std::tuple<Args...>>(params);
         auto args = std::tuple_cat(std::make_tuple(current_context_), args_tuple);
         auto function = reinterpret_cast<void (*)(void *, Args...)>(func_data->raw_func_);
         std::apply(function, args);
-        if (func_data->vm_->cmpLogLevel(LogLevel::trace)) {
+        if (log) {
           func_data->vm_->integration()->trace("[vm<-host] " + func_data->name_ + " return: void");
         }
         return nullptr;
@@ -682,7 +683,8 @@ void V8::registerHostFunctionImpl(std::string_view module_name, std::string_view
       store_.get(), type.get(),
       [](void *data, const wasm::Val params[], wasm::Val results[]) -> wasm::own<wasm::Trap> {
         auto func_data = reinterpret_cast<FuncData *>(data);
-        if (func_data->vm_->cmpLogLevel(LogLevel::trace)) {
+        const bool log = func_data->vm_->cmpLogLevel(LogLevel::trace);
+        if (log) {
           func_data->vm_->integration()->trace("[vm->host] " + func_data->name_ + "(" +
                                                printValues(params, sizeof...(Args)) + ")");
         }
@@ -691,7 +693,7 @@ void V8::registerHostFunctionImpl(std::string_view module_name, std::string_view
         auto function = reinterpret_cast<R (*)(void *, Args...)>(func_data->raw_func_);
         R rvalue = std::apply(function, args);
         results[0] = makeVal(rvalue);
-        if (func_data->vm_->cmpLogLevel(LogLevel::trace)) {
+        if (log) {
           func_data->vm_->integration()->trace("[vm<-host] " + func_data->name_ +
                                                " return: " + std::to_string(rvalue));
         }
@@ -729,17 +731,18 @@ void V8::getModuleFunctionImpl(std::string_view function_name,
   }
   *function = [func, function_name, this](ContextBase *context, Args... args) -> void {
     wasm::Val params[] = {makeVal(args)...};
-    SaveRestoreContext saved_context(context);
-    if (cmpLogLevel(LogLevel::trace)) {
+    const bool log = cmpLogLevel(LogLevel::trace);
+    if (log) {
       integration()->trace("[host->vm] " + std::string(function_name) + "(" +
                            printValues(params, sizeof...(Args)) + ")");
     }
+    SaveRestoreContext saved_context(context);
     auto trap = func->call(params, nullptr);
     if (trap) {
       fail(FailState::RuntimeError, getFailMessage(std::string(function_name), std::move(trap)));
       return;
     }
-    if (cmpLogLevel(LogLevel::trace)) {
+    if (log) {
       integration()->trace("[host<-vm] " + std::string(function_name) + " return: void");
     }
   };
@@ -769,18 +772,19 @@ void V8::getModuleFunctionImpl(std::string_view function_name,
   *function = [func, function_name, this](ContextBase *context, Args... args) -> R {
     wasm::Val params[] = {makeVal(args)...};
     wasm::Val results[1];
-    SaveRestoreContext saved_context(context);
-    if (cmpLogLevel(LogLevel::trace)) {
+    const bool log = cmpLogLevel(LogLevel::trace);
+    if (log) {
       integration()->trace("[host->vm] " + std::string(function_name) + "(" +
                            printValues(params, sizeof...(Args)) + ")");
     }
+    SaveRestoreContext saved_context(context);
     auto trap = func->call(params, results);
     if (trap) {
       fail(FailState::RuntimeError, getFailMessage(std::string(function_name), std::move(trap)));
       return R{};
     }
     R rvalue = results[0].get<typename ConvertWordTypeToUint32<R>::type>();
-    if (cmpLogLevel(LogLevel::trace)) {
+    if (log) {
       integration()->trace("[host<-vm] " + std::string(function_name) +
                            " return: " + std::to_string(rvalue));
     }