Fix vtunejit issues

This change fixes two issues with VTune JIT Profiling API.

1. Update way of setting flag "--no-compact-code-space" to avoid changing flags after initialization v8.
2. Fix a crash from visiting uninitialized ptr.

Change-Id: I4878ffd554ce53630db961fe09b49e081b0091bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3787321Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Fanchen Kong <fanchen.kong@intel.com>
Cr-Commit-Position: refs/heads/main@{#82003}

include/v8-callbacks.h

@@ -106,7 +106,7 @@ struct JitCodeEvent {
     size_t line_number_table_size;
   };
 
-  wasm_source_info_t* wasm_source_info;
+  wasm_source_info_t* wasm_source_info = nullptr;
 
   union {
     // Only valid for CODE_ADDED.

src/d8/d8.cc

@@ -5648,7 +5648,9 @@ int Shell::Main(int argc, char* argv[]) {
   }
   create_params.array_buffer_allocator = Shell::array_buffer_allocator;
 #ifdef ENABLE_VTUNE_JIT_INTERFACE
-  create_params.code_event_handler = vTune::GetVtuneCodeEventHandler();
+  if (i::FLAG_enable_vtunejit) {
+    create_params.code_event_handler = vTune::GetVtuneCodeEventHandler();
+  }
 #endif
   create_params.constraints.ConfigureDefaults(
       base::SysInfo::AmountOfPhysicalMemory(),

src/flags/flag-definitions.h

@@ -1582,6 +1582,11 @@ DEFINE_STRING(expose_cputracemark_as, nullptr,
 DEFINE_BOOL(enable_vtune_domain_support, true, "enable vtune domain support")
 #endif  // ENABLE_VTUNE_TRACEMARK
 
+#ifdef ENABLE_VTUNE_JIT_INTERFACE
+DEFINE_BOOL(enable_vtunejit, true, "enable vtune jit interface")
+DEFINE_NEG_IMPLICATION(enable_vtunejit, compact_code_space)
+#endif  // ENABLE_VTUNE_JIT_INTERFACE
+
 // builtins.cc
 DEFINE_BOOL(allow_unsafe_function_constructor, false,
             "allow invoking the function constructor without security checks")

src/third_party/vtune/vtune-jit.cc

@@ -295,7 +295,6 @@ void VTUNEJITInterface::event_handler(const v8::JitCodeEvent* event) {
 }  // namespace internal
 
 v8::JitCodeEventHandler GetVtuneCodeEventHandler() {
-  v8::V8::SetFlagsFromString("--no-compact-code-space");
   return vTune::internal::VTUNEJITInterface::event_handler;
 }