[lldb][swift] Add target option for caching task ptr locations

This is a useful fallback for debugging.

Author: felipepiovezan

lldb/include/lldb/Target/Target.h

@@ -201,6 +201,8 @@ class TargetProperties : public Properties {
 
   bool GetSwiftUseTasksPlugin() const;
 
+  bool GetSwiftCacheTaskPointerLocation() const;
+
   Args GetSwiftPluginServerForPath() const;
 
   bool GetSwiftAutoImportFrameworks() const;

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp

@@ -3017,7 +3017,8 @@ TaskInspector::GetTaskAddrFromThreadLocalStorage(Thread &thread) {
   // If the read from this TLS address is successful, cache the TLS address.
   // Caching without a valid read is dangerous: earlier in the thread
   // lifetime, the result of GetExtendedInfo can be invalid.
-  if (task_addr)
+  if (task_addr &&
+      real_thread.GetProcess()->GetTarget().GetSwiftCacheTaskPointerLocation())
     m_tid_to_task_addr_location.try_emplace(real_thread.GetID(),
                                             *task_addr_location);
   return task_addr;

lldb/source/Target/Target.cpp

@@ -4529,6 +4529,18 @@ bool TargetProperties::GetSwiftUseTasksPlugin() const {
   return true;
 }
 
+bool TargetProperties::GetSwiftCacheTaskPointerLocation() const {
+  const Property *exp_property =
+      m_collection_sp->GetPropertyAtIndex(ePropertyExperimental);
+  OptionValueProperties *exp_values =
+      exp_property->GetValue()->GetAsProperties();
+  if (exp_values)
+    return exp_values
+        ->GetPropertyAtIndexAs<bool>(ePropertySwiftCacheTaskPointerLocation)
+        .value_or(true);
+  return true;
+}
+
 Args TargetProperties::GetSwiftPluginServerForPath() const {
   const uint32_t idx = ePropertySwiftPluginServerForPath;
 

lldb/source/Target/TargetProperties.td

@@ -34,6 +34,9 @@ let Definition = "target_experimental" in {
   def SwiftUseTasksPlugin: Property<"swift-tasks-plugin-enabled", "Boolean">,
     DefaultTrue,
     Desc<"Enables the swift plugin converting tasks into threads">;
+  def SwiftCacheTaskPointerLocation: Property<"swift-cache-task-pointer-location", "Boolean">,
+    DefaultTrue,
+    Desc<"Enables caching of task pointers inside the swift tasks plugin">;
 }
 
 let Definition = "target" in {