[lldb] Use std::make_shared for StopInfoSP

[JDevlieghere]

Use std::make_shared to create a StopInfoSP, which inherits from shared_from_this. It's both the most efficient and safest way to create these objects:

• With make_shared, the object and the control block are allocated together, which is more efficient.
• With make_shared, the enable_shared_from_this base class is properly linked to the control block before the constructor finishes, so shared_from_this() will be safe to use (though still not recommended during construction).

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Jonas Devlieghere (JDevlieghere)

Changes

Use std::make_shared to create a StopInfoSP, which inherits from shared_from_this. It's both the most efficient and safest way to create these objects:

• With make_shared, the object and the control block are allocated together, which is more efficient.
• With make_shared, the enable_shared_from_this base class is properly linked to the control block before the constructor finishes, so shared_from_this() will be safe to use (though still not recommended during construction).

---

Full diff: https://github.com/llvm/llvm-project/pull/149612.diff

1 Files Affected:

• (modified) lldb/source/Target/StopInfo.cpp (+18-17)

diff --git a/lldb/source/Target/StopInfo.cpp b/lldb/source/Target/StopInfo.cpp
index 19f89b8246926..240e75a414c63 100644
--- a/lldb/source/Target/StopInfo.cpp
+++ b/lldb/source/Target/StopInfo.cpp
@@ -851,8 +851,9 @@ class StopInfoWatchpoint : public StopInfo {
       // We have to step over the watchpoint before we know what to do:   
       StopInfoWatchpointSP me_as_siwp_sp 
           = std::static_pointer_cast<StopInfoWatchpoint>(shared_from_this());
-      ThreadPlanSP step_over_wp_sp(new ThreadPlanStepOverWatchpoint(
-          *(thread_sp.get()), me_as_siwp_sp, wp_sp));
+      ThreadPlanSP step_over_wp_sp =
+          std::make_shared<ThreadPlanStepOverWatchpoint>(*(thread_sp.get()),
+                                                         me_as_siwp_sp, wp_sp);
       // When this plan is done we want to stop, so set this as a Controlling
       // plan.    
       step_over_wp_sp->SetIsControllingPlan(true);
@@ -1475,13 +1476,13 @@ StopInfoSP StopInfo::CreateStopReasonWithBreakpointSiteID(Thread &thread,
                                                           break_id_t break_id) {
   thread.SetThreadHitBreakpointSite();
 
-  return StopInfoSP(new StopInfoBreakpoint(thread, break_id));
+  return std::make_shared<StopInfoBreakpoint>(thread, break_id);
 }
 
 StopInfoSP StopInfo::CreateStopReasonWithBreakpointSiteID(Thread &thread,
                                                           break_id_t break_id,
                                                           bool should_stop) {
-  return StopInfoSP(new StopInfoBreakpoint(thread, break_id, should_stop));
+  return std::make_shared<StopInfoBreakpoint>(thread, break_id, should_stop);
 }
 
 // LWP_TODO: We'll need a CreateStopReasonWithWatchpointResourceID akin
@@ -1489,20 +1490,20 @@ StopInfoSP StopInfo::CreateStopReasonWithBreakpointSiteID(Thread &thread,
 StopInfoSP StopInfo::CreateStopReasonWithWatchpointID(Thread &thread,
                                                       break_id_t watch_id,
                                                       bool silently_continue) {
-  return StopInfoSP(
-      new StopInfoWatchpoint(thread, watch_id, silently_continue));
+  return std::make_shared<StopInfoWatchpoint>(thread, watch_id,
+                                              silently_continue);
 }
 
 StopInfoSP StopInfo::CreateStopReasonWithSignal(Thread &thread, int signo,
                                                 const char *description,
                                                 std::optional<int> code) {
   thread.GetProcess()->GetUnixSignals()->IncrementSignalHitCount(signo);
-  return StopInfoSP(new StopInfoUnixSignal(thread, signo, description, code));
+  return std::make_shared<StopInfoUnixSignal>(thread, signo, description, code);
 }
 
 StopInfoSP StopInfo::CreateStopReasonWithInterrupt(Thread &thread, int signo,
                                                    const char *description) {
-  return StopInfoSP(new StopInfoInterrupt(thread, signo, description));
+  return std::make_shared<StopInfoInterrupt>(thread, signo, description);
 }
 
 StopInfoSP StopInfo::CreateStopReasonToTrace(Thread &thread) {
@@ -1512,44 +1513,44 @@ StopInfoSP StopInfo::CreateStopReasonToTrace(Thread &thread) {
 StopInfoSP StopInfo::CreateStopReasonWithPlan(
     ThreadPlanSP &plan_sp, ValueObjectSP return_valobj_sp,
     ExpressionVariableSP expression_variable_sp) {
-  return StopInfoSP(new StopInfoThreadPlan(plan_sp, return_valobj_sp,
-                                           expression_variable_sp));
+  return std::make_shared<StopInfoThreadPlan>(plan_sp, return_valobj_sp,
+                                              expression_variable_sp);
 }
 
 StopInfoSP StopInfo::CreateStopReasonWithException(Thread &thread,
                                                    const char *description) {
-  return StopInfoSP(new StopInfoException(thread, description));
+  return std::make_shared<StopInfoException>(thread, description);
 }
 
 StopInfoSP StopInfo::CreateStopReasonProcessorTrace(Thread &thread,
                                                     const char *description) {
-  return StopInfoSP(new StopInfoProcessorTrace(thread, description));
+  return std::make_shared<StopInfoProcessorTrace>(thread, description);
 }
 
 StopInfoSP StopInfo::CreateStopReasonHistoryBoundary(Thread &thread,
                                                      const char *description) {
-  return StopInfoSP(new StopInfoHistoryBoundary(thread, description));
+  return std::make_shared<StopInfoHistoryBoundary>(thread, description);
 }
 
 StopInfoSP StopInfo::CreateStopReasonWithExec(Thread &thread) {
-  return StopInfoSP(new StopInfoExec(thread));
+  return std::make_shared<StopInfoExec>(thread);
 }
 
 StopInfoSP StopInfo::CreateStopReasonFork(Thread &thread,
                                           lldb::pid_t child_pid,
                                           lldb::tid_t child_tid) {
-  return StopInfoSP(new StopInfoFork(thread, child_pid, child_tid));
+  return std::make_shared<StopInfoFork>(thread, child_pid, child_tid);
 }
 
 
 StopInfoSP StopInfo::CreateStopReasonVFork(Thread &thread,
                                            lldb::pid_t child_pid,
                                            lldb::tid_t child_tid) {
-  return StopInfoSP(new StopInfoVFork(thread, child_pid, child_tid));
+  return std::make_shared<StopInfoVFork>(thread, child_pid, child_tid);
 }
 
 StopInfoSP StopInfo::CreateStopReasonVForkDone(Thread &thread) {
-  return StopInfoSP(new StopInfoVForkDone(thread));
+  return std::make_shared<StopInfoVForkDone>(thread);
 }
 
 ValueObjectSP StopInfo::GetReturnValueObject(StopInfoSP &stop_info_sp) {

[jimingham]

LGTM. If there were somewhere that this could be documented so somebody won't make the same mistake, that would be a bonus. But this is fine on its own.

[JDevlieghere]

LGTM. If there were somewhere that this could be documented so somebody won't make the same mistake, that would be a bonus. But this is fine on its own.

I think the preference for make_shared and make_unique is fairly universally accepted. The code here looks like legacy code that likely just predated that.

[jimingham]

Sounds good. A lot of this code was written before C++11 was available, so that's to be expected.