[Lldb-commits] [lldb] b6bf27e - Avoid expression evaluation in libStdC++ std::vector<bool> synthetic children provider (#108414)

[via lldb-commits]

Author: jeffreytan81
Date: 2024-09-13T10:26:01-07:00
New Revision: b6bf27ef3c179eefd805f39aa681705fc980ceed

URL: https://github.com/llvm/llvm-project/commit/b6bf27ef3c179eefd805f39aa681705fc980ceed
DIFF: https://github.com/llvm/llvm-project/commit/b6bf27ef3c179eefd805f39aa681705fc980ceed.diff

LOG: Avoid expression evaluation in libStdC++ std::vector<bool> synthetic children provider  (#108414)

Our customers is reporting a serious performance issue (expanding a this
pointer takes 70 seconds in VSCode) in a specific execution context.

Profiling shows the hot path is triggered by an expression evaluation
from libStdC++ synthetic children provider for `std::vector<bool>` since
it uses `CreateValueFromExpression()`.

This PR added a new `SBValue::CreateBoolValue()` API and switch
`std::vector<bool>` synthetic children provider to use the new API
without performing expression evaluation.

Note: there might be other cases of `CreateValueFromExpression()` in our
summary/synthetic children providers which I will sweep through in later
PRs.

With this PR, the customer's scenario reduces from 70 seconds => 50
seconds. I will add other PRs to further optimize the remaining 50
seconds (mostly from type/namespace lookup).

Testing:

`test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/vbool/TestDataFormatterStdVBool.py`
passes with the PR

---------

Co-authored-by: jeffreytan81 <jeffreytan at fb.com>

Added: 
    

Modified: 
    lldb/examples/synthetic/gnu_libstdcpp.py
    lldb/include/lldb/API/SBValue.h
    lldb/source/API/SBValue.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/examples/synthetic/gnu_libstdcpp.py b/lldb/examples/synthetic/gnu_libstdcpp.py
index d98495b8a9df38..a6605a7a7eb5b3 100644
--- a/lldb/examples/synthetic/gnu_libstdcpp.py
+++ b/lldb/examples/synthetic/gnu_libstdcpp.py
@@ -473,11 +473,7 @@ def get_child_at_index(self, index):
                 "[" + str(index) + "]", element_offset, element_type
             )
             bit = element.GetValueAsUnsigned(0) & (1 << bit_offset)
-            if bit != 0:
-                value_expr = "(bool)true"
-            else:
-                value_expr = "(bool)false"
-            return self.valobj.CreateValueFromExpression("[%d]" % index, value_expr)
+            return self.valobj.CreateBoolValue("[%d]" % index, bool(bit))
 
         def update(self):
             try:

diff  --git a/lldb/include/lldb/API/SBValue.h b/lldb/include/lldb/API/SBValue.h
index bec816fb451844..9090cece80f7ce 100644
--- a/lldb/include/lldb/API/SBValue.h
+++ b/lldb/include/lldb/API/SBValue.h
@@ -145,6 +145,8 @@ class LLDB_API SBValue {
   // AddressOf() on the return of this call all return invalid
   lldb::SBValue CreateValueFromData(const char *name, lldb::SBData data,
                                     lldb::SBType type);
+  // Returned value has no address.
+  lldb::SBValue CreateBoolValue(const char *name, bool value);
 
   /// Get a child value by index from a value.
   ///

diff  --git a/lldb/source/API/SBValue.cpp b/lldb/source/API/SBValue.cpp
index 273aac5ad47989..e1a31708d46ffb 100644
--- a/lldb/source/API/SBValue.cpp
+++ b/lldb/source/API/SBValue.cpp
@@ -645,6 +645,22 @@ lldb::SBValue SBValue::CreateValueFromData(const char *name, SBData data,
   return sb_value;
 }
 
+lldb::SBValue SBValue::CreateBoolValue(const char *name, bool value) {
+  LLDB_INSTRUMENT_VA(this, name);
+
+  lldb::SBValue sb_value;
+  lldb::ValueObjectSP new_value_sp;
+  ValueLocker locker;
+  lldb::ValueObjectSP value_sp(GetSP(locker));
+  lldb::TargetSP target_sp = m_opaque_sp->GetTargetSP();
+  if (value_sp && target_sp) {
+    new_value_sp =
+        ValueObject::CreateValueObjectFromBool(target_sp, value, name);
+  }
+  sb_value.SetSP(new_value_sp);
+  return sb_value;
+}
+
 SBValue SBValue::GetChildAtIndex(uint32_t idx) {
   LLDB_INSTRUMENT_VA(this, idx);