[lldb] Do not bump memory modificator ID when "internal" debugger memory is updated (llvm#129092)

This change adds a setting `target.process.track-memory-cache-changes`.
Disabling this setting prevents invalidating and updating values in
`ValueObject::UpdateValueIfNeeded` when only "internal" debugger memory
is updated. Writing to "internal" debugger memory happens when, for
instance, expressions are evaluated by visualizers (pretty printers).
One of the examples when cache invalidation has a particularly heavy
impact is visualizations of some collections: in some collections
getting collection size is an expensive operation (it requires traversal
of the collection).
At the same time evaluating user expression with side effects (visible
to target, not only to debugger) will still bump memory ID because:

- If expression is evaluated via interpreter: it will cause write to
"non-internal" memory
- If expression is JIT-compiled: then to call the function LLDB will
write to "non-internal" stack memory

The downside of disabled `target.process.track-memory-cache-changes`
setting is that convenience variables won't reevaluate synthetic
children automatically.

---------

Co-authored-by: Mikhail Zakharov <[email protected]>

Author: real-mikhail

lldb/include/lldb/Target/Memory.h

@@ -125,6 +125,8 @@ class AllocatedMemoryCache {
 
   bool DeallocateMemory(lldb::addr_t ptr);
 
+  bool IsInCache(lldb::addr_t addr) const;
+
 protected:
   typedef std::shared_ptr<AllocatedBlock> AllocatedBlockSP;
 
@@ -133,7 +135,7 @@ class AllocatedMemoryCache {
 
   // Classes that inherit from MemoryCache can see and modify these
   Process &m_process;
-  std::recursive_mutex m_mutex;
+  mutable std::recursive_mutex m_mutex;
   typedef std::multimap<uint32_t, AllocatedBlockSP> PermissionsToBlockMap;
   PermissionsToBlockMap m_memory_map;
 

lldb/include/lldb/Target/Process.h

@@ -111,6 +111,7 @@ class ProcessProperties : public Properties {
   void SetOSPluginReportsAllThreads(bool does_report);
   bool GetSteppingRunsAllThreads() const;
   FollowForkMode GetFollowForkMode() const;
+  bool TrackMemoryCacheChanges() const;
 
 protected:
   Process *m_process; // Can be nullptr for global ProcessProperties
@@ -312,6 +313,18 @@ class ProcessModID {
     return lldb::EventSP();
   }
 
+  void Dump(Stream &stream) const {
+    stream.Format("ProcessModID:\n"
+                  "  m_stop_id: {0}\n  m_last_natural_stop_id: {1}\n"
+                  "  m_resume_id: {2}\n  m_memory_id: {3}\n"
+                  "  m_last_user_expression_resume: {4}\n"
+                  "  m_running_user_expression: {5}\n"
+                  "  m_running_utility_function: {6}\n",
+                  m_stop_id, m_last_natural_stop_id, m_resume_id, m_memory_id,
+                  m_last_user_expression_resume, m_running_user_expression,
+                  m_running_utility_function);
+  }
+
 private:
   uint32_t m_stop_id = 0;
   uint32_t m_last_natural_stop_id = 0;

lldb/source/Commands/CommandObjectProcess.cpp

@@ -1388,6 +1388,9 @@ class CommandObjectProcessStatus : public CommandObjectParsed {
       case 'v':
         m_verbose = true;
         break;
+      case 'd':
+        m_dump = true;
+        break;
       default:
         llvm_unreachable("Unimplemented option");
       }
@@ -1397,6 +1400,7 @@ class CommandObjectProcessStatus : public CommandObjectParsed {
 
     void OptionParsingStarting(ExecutionContext *execution_context) override {
       m_verbose = false;
+      m_dump = false;
     }
 
     llvm::ArrayRef<OptionDefinition> GetDefinitions() override {
@@ -1405,6 +1409,7 @@ class CommandObjectProcessStatus : public CommandObjectParsed {
 
     // Instance variables to hold the values for command options.
     bool m_verbose = false;
+    bool m_dump = false;
   };
 
 protected:
@@ -1459,6 +1464,14 @@ class CommandObjectProcessStatus : public CommandObjectParsed {
         crash_info_sp->GetDescription(strm);
       }
     }
+
+    if (m_options.m_dump) {
+      StateType state = process->GetState();
+      if (state == eStateStopped) {
+        ProcessModID process_mod_id = process->GetModID();
+        process_mod_id.Dump(result.GetOutputStream());
+      }
+    }
   }
 
 private:

lldb/source/Commands/Options.td

@@ -788,6 +788,8 @@ let Command = "process handle" in {
 let Command = "process status" in {
   def process_status_verbose : Option<"verbose", "v">, Group<1>,
     Desc<"Show verbose process status including extended crash information.">;
+  def process_status_dump : Option<"dump-modification-id", "d">, Group<1>,
+    Desc<"Dump the state of the ProcessModID of the stopped process.">;
 }
 
 let Command = "process save_core" in {

lldb/source/Target/Memory.cpp

@@ -433,3 +433,11 @@ bool AllocatedMemoryCache::DeallocateMemory(lldb::addr_t addr) {
             (uint64_t)addr, success);
   return success;
 }
+
+bool AllocatedMemoryCache::IsInCache(lldb::addr_t addr) const {
+  std::lock_guard guard(m_mutex);
+
+  return llvm::any_of(m_memory_map, [addr](const auto &block) {
+    return block.second->Contains(addr);
+  });
+}

lldb/source/Target/Process.cpp

@@ -370,6 +370,12 @@ FollowForkMode ProcessProperties::GetFollowForkMode() const {
                g_process_properties[idx].default_uint_value));
 }
 
+bool ProcessProperties::TrackMemoryCacheChanges() const {
+  const uint32_t idx = ePropertyTrackMemoryCacheChanges;
+  return GetPropertyAtIndexAs<bool>(
+      idx, g_process_properties[idx].default_uint_value != 0);
+}
+
 ProcessSP Process::FindPlugin(lldb::TargetSP target_sp,
                               llvm::StringRef plugin_name,
                               ListenerSP listener_sp,
@@ -2285,6 +2291,7 @@ size_t Process::WriteMemoryPrivate(addr_t addr, const void *buf, size_t size,
   return bytes_written;
 }
 
+#define USE_ALLOCATE_MEMORY_CACHE 1
 size_t Process::WriteMemory(addr_t addr, const void *buf, size_t size,
                             Status &error) {
   if (ABISP abi_sp = GetABI())
@@ -2297,7 +2304,12 @@ size_t Process::WriteMemory(addr_t addr, const void *buf, size_t size,
   if (buf == nullptr || size == 0)
     return 0;
 
+#if defined(USE_ALLOCATE_MEMORY_CACHE)
+  if (TrackMemoryCacheChanges() || !m_allocated_memory_cache.IsInCache(addr))
+    m_mod_id.BumpMemoryID();
+#else
   m_mod_id.BumpMemoryID();
+#endif
 
   // We need to write any data that would go where any current software traps
   // (enabled software breakpoints) any software traps (breakpoints) that we
@@ -2426,7 +2438,6 @@ Status Process::WriteObjectFile(std::vector<ObjectFile::LoadableData> entries) {
   return error;
 }
 
-#define USE_ALLOCATE_MEMORY_CACHE 1
 addr_t Process::AllocateMemory(size_t size, uint32_t permissions,
                                Status &error) {
   if (GetPrivateState() != eStateStopped) {

lldb/source/Target/TargetProperties.td

@@ -299,6 +299,9 @@ let Definition = "process" in {
     DefaultEnumValue<"eFollowParent">,
     EnumValues<"OptionEnumValues(g_follow_fork_mode_values)">,
     Desc<"Debugger's behavior upon fork or vfork.">;
+  def TrackMemoryCacheChanges: Property<"track-memory-cache-changes", "Boolean">,
+    DefaultTrue,
+    Desc<"If true, memory cache modifications (which happen often during expressions evaluation) will bump process state ID (and invalidate all synthetic children). Disabling this option helps to avoid synthetic children reevaluation when pretty printers heavily use expressions. The downside of disabled setting is that convenience variables won't reevaluate synthetic children automatically.">;
 }
 
 let Definition = "platform" in {

lldb/test/API/commands/settings/TestSettings.py

@@ -905,6 +905,7 @@ def test_all_settings_exist(self):
                 "target.use-hex-immediates",
                 "target.process.disable-memory-cache",
                 "target.process.extra-startup-command",
+                "target.process.track-memory-cache-changes",
                 "target.process.thread.trace-thread",
                 "target.process.thread.step-avoid-regexp",
             ],

lldb/test/Shell/Expr/TestExprWithSideEffect.cpp

@@ -0,0 +1,55 @@
+// Tests evaluating expressions with side effects.
+// Applied side effect should be visible to the debugger.
+
+// RUN: %build %s -o %t
+// RUN: %lldb %t \
+// RUN:   -o "settings set target.process.track-memory-cache-changes false" \
+// RUN:   -o "run" \
+// RUN:   -o "frame variable x" \
+// RUN:   -o "expr x.inc()" \
+// RUN:   -o "frame variable x" \
+// RUN:   -o "continue" \
+// RUN:   -o "frame variable x" \
+// RUN:   -o "expr x.i = 10" \
+// RUN:   -o "frame variable x" \
+// RUN:   -o "continue" \
+// RUN:   -o "frame variable x" \
+// RUN:   -o "exit" | FileCheck %s -dump-input=fail
+
+class X {
+  int i = 0;
+
+public:
+  void inc() { ++i; }
+};
+
+int main() {
+  X x;
+  x.inc();
+
+  __builtin_debugtrap();
+  __builtin_debugtrap();
+  __builtin_debugtrap();
+  return 0;
+}
+
+// CHECK-LABEL: frame variable x
+// CHECK: (X) x = (i = 1)
+
+// CHECK-LABEL: expr x.inc()
+// CHECK-LABEL: frame variable x
+// CHECK: (X) x = (i = 2)
+
+// CHECK-LABEL: continue
+// CHECK-LABEL: frame variable x
+// CHECK: (X) x = (i = 2)
+
+// CHECK-LABEL: expr x.i = 10
+// CHECK: (int) $0 = 10
+
+// CHECK-LABEL: frame variable x
+// CHECK: (X) x = (i = 10)
+
+// CHECK-LABEL: continue
+// CHECK-LABEL: frame variable x
+// CHECK: (X) x = (i = 10)

lldb/test/Shell/Expr/TestExprWithSideEffectOnConvenienceVar.cpp

@@ -0,0 +1,52 @@
+// Tests evaluating expressions with side effects on convenience variable.
+// Applied side effect should be visible to the debugger.
+
+// UNSUPPORTED: system-windows
+
+// RUN: %build %s -o %t
+// RUN: %lldb %t \
+// RUN:   -o "settings set target.process.track-memory-cache-changes false" \
+// RUN:   -o "run" \
+// RUN:   -o "expr int \$y = 11" \
+// RUN:   -o "expr \$y" \
+// RUN:   -o "expr \$y = 100" \
+// RUN:   -o "expr \$y" \
+// RUN:   -o "continue" \
+// RUN:   -o "expr \$y" \
+// RUN:   -o "expr X \$mine = {100, 200}" \
+// RUN:   -o "expr \$mine.a = 300" \
+// RUN:   -o "expr \$mine" \
+// RUN:   -o "exit" | FileCheck %s -dump-input=fail
+
+struct X {
+  int a;
+  int b;
+};
+
+int main() {
+  X x;
+
+  __builtin_debugtrap();
+  __builtin_debugtrap();
+  return 0;
+}
+
+// CHECK-LABEL: expr int $y = 11
+// CHECK-LABEL: expr $y
+// CHECK: (int) $y = 11
+
+// CHECK-LABEL: expr $y = 100
+// CHECK: (int) $0 = 100
+
+// CHECK-LABEL: expr $y
+// CHECK: (int) $y = 100
+
+// CHECK-LABEL: continue
+// CHECK-LABEL: expr $y
+// CHECK: (int) $y = 100
+
+// CHECK-LABEL: expr X $mine = {100, 200}
+// CHECK-LABEL: expr $mine.a = 300
+// CHECK: (int) $1 = 300
+// CHECK-LABEL: expr $mine
+// CHECK: (X) $mine = (a = 300, b = 200)