Speed up accelerator table lookups

When debugging a large program like clang and doing "frame variable
*this", the ValueObject pretty printer is doing hundreds of scoped
FindTypes lookups. The ones that take longest are the ones where the
DWARFDeclContext ends in something like ::Iterator which produces many
false positives that need to be filtered out *after* extracting the
DIEs. This patch demonstrates a way to filter out false positives at
the accerator table lookup step.

With this patch
  lldb clang-10 -o "b EmitFunctionStart" -o r -o "f 2" -o "fr v *this" -b -- ...
goes (in user time) from 5.6s -> 4.8s
or (in wall clock) from 6.9s -> 6.0s.

Differential Revision: https://reviews.llvm.org/D68678

llvm-svn: 374401

1 files changed, 24 insertions, 3 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.cpp b/lldb/source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.cpp
index 97dbd6c4b90a..0a5073b8cd9e 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.cpp
@@ -110,6 +110,7 @@ void AppleDWARFIndex::GetTypes(const DWARFDeclContext &context,
   const bool has_qualified_name_hash =
       m_apple_types_up->GetHeader().header_data.ContainsAtom(
           DWARFMappedHash::eAtomTypeQualNameHash);
+
   const ConstString type_name(context[0].name);
   const dw_tag_t tag = context[0].tag;
   if (has_tag && has_qualified_name_hash) {
@@ -119,12 +120,32 @@ void AppleDWARFIndex::GetTypes(const DWARFDeclContext &context,
       m_module.LogMessage(log, "FindByNameAndTagAndQualifiedNameHash()");
     m_apple_types_up->FindByNameAndTagAndQualifiedNameHash(
         type_name.GetStringRef(), tag, qualified_name_hash, offsets);
-  } else if (has_tag) {
+    return;
+  }
+
+  if (has_tag) {
+    // When searching for a scoped type (for example,
+    // "std::vector<int>::const_iterator") searching for the innermost
+    // name alone ("const_iterator") could yield many false
+    // positives. By searching for the parent type ("vector<int>")
+    // first we can avoid extracting type DIEs from object files that
+    // would fail the filter anyway.
+    if (!has_qualified_name_hash && (context.GetSize() > 1) &&
+        (context[1].tag == DW_TAG_class_type ||
+         context[1].tag == DW_TAG_structure_type)) {
+      DIEArray class_matches;
+      m_apple_types_up->FindByName(context[1].name, class_matches);
+      if (class_matches.empty())
+        return;
+    }
+
     if (log)
       m_module.LogMessage(log, "FindByNameAndTag()");
     m_apple_types_up->FindByNameAndTag(type_name.GetStringRef(), tag, offsets);
-  } else
-    m_apple_types_up->FindByName(type_name.GetStringRef(), offsets);
+    return;
+  }
+
+  m_apple_types_up->FindByName(type_name.GetStringRef(), offsets);
 }
 
 void AppleDWARFIndex::GetNamespaces(ConstString name, DIEArray &offsets) {