[lldb][NFCI] Remove use of ConstString in StructuredData

The remaining use of ConstString in StructuredData is the Dictionary
class. Internally it's backed by a `std::map<ConstString, ObjectSP>`.
I propose that we replace it with a `llvm::StringMap<ObjectSP>`.

Many StructuredData::Dictionary objects are ephemeral and only exist for
a short amount of time. Many of these Dictionaries are only produced
once and are never used again. That leaves us with a lot of string data
in the ConstString StringPool that is sitting there never to be used
again. Even if the same string is used many times for keys of different
Dictionary objects, that is something we can measure and adjust for
instead of assuming that every key may be reused at some point in the
future.

Quick comparisons of key data is likely not a concern with Dictionary,
but the use of `llvm::StringMap` means that lookups should be fast with
its hashing strategy.

Switching to a llvm::StringMap meant that the iteration order may be
different. To account for this when serializing/dumping the dictionary,
I added some code to sort the output by key before emitting anything.

Differential Revision: https://reviews.llvm.org/D159313

1 files changed, 19 insertions, 20 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index 8ca2072..2fc446b 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -1926,24 +1926,23 @@ ThreadSP ProcessGDBRemote::SetThreadStopInfo(
 
 lldb::ThreadSP
 ProcessGDBRemote::SetThreadStopInfo(StructuredData::Dictionary *thread_dict) {
-  static ConstString g_key_tid("tid");
-  static ConstString g_key_name("name");
-  static ConstString g_key_reason("reason");
-  static ConstString g_key_metype("metype");
-  static ConstString g_key_medata("medata");
-  static ConstString g_key_qaddr("qaddr");
-  static ConstString g_key_dispatch_queue_t("dispatch_queue_t");
-  static ConstString g_key_associated_with_dispatch_queue(
+  static constexpr llvm::StringLiteral g_key_tid("tid");
+  static constexpr llvm::StringLiteral g_key_name("name");
+  static constexpr llvm::StringLiteral g_key_reason("reason");
+  static constexpr llvm::StringLiteral g_key_metype("metype");
+  static constexpr llvm::StringLiteral g_key_medata("medata");
+  static constexpr llvm::StringLiteral g_key_qaddr("qaddr");
+  static constexpr llvm::StringLiteral g_key_dispatch_queue_t(
+      "dispatch_queue_t");
+  static constexpr llvm::StringLiteral g_key_associated_with_dispatch_queue(
       "associated_with_dispatch_queue");
-  static ConstString g_key_queue_name("qname");
-  static ConstString g_key_queue_kind("qkind");
-  static ConstString g_key_queue_serial_number("qserialnum");
-  static ConstString g_key_registers("registers");
-  static ConstString g_key_memory("memory");
-  static ConstString g_key_address("address");
-  static ConstString g_key_bytes("bytes");
-  static ConstString g_key_description("description");
-  static ConstString g_key_signal("signal");
+  static constexpr llvm::StringLiteral g_key_queue_name("qname");
+  static constexpr llvm::StringLiteral g_key_queue_kind("qkind");
+  static constexpr llvm::StringLiteral g_key_queue_serial_number("qserialnum");
+  static constexpr llvm::StringLiteral g_key_registers("registers");
+  static constexpr llvm::StringLiteral g_key_memory("memory");
+  static constexpr llvm::StringLiteral g_key_description("description");
+  static constexpr llvm::StringLiteral g_key_signal("signal");
 
   // Stop with signal and thread info
   lldb::tid_t tid = LLDB_INVALID_THREAD_ID;
@@ -1971,7 +1970,7 @@ ProcessGDBRemote::SetThreadStopInfo(StructuredData::Dictionary *thread_dict) {
                         &thread_dispatch_qaddr, &queue_vars_valid,
                         &associated_with_dispatch_queue, &dispatch_queue_t,
                         &queue_name, &queue_kind, &queue_serial_number](
-                           ConstString key,
+                           llvm::StringRef key,
                            StructuredData::Object *object) -> bool {
     if (key == g_key_tid) {
       // thread in big endian hex
@@ -2029,10 +2028,10 @@ ProcessGDBRemote::SetThreadStopInfo(StructuredData::Dictionary *thread_dict) {
 
       if (registers_dict) {
         registers_dict->ForEach(
-            [&expedited_register_map](ConstString key,
+            [&expedited_register_map](llvm::StringRef key,
                                       StructuredData::Object *object) -> bool {
               uint32_t reg;
-              if (llvm::to_integer(key.AsCString(), reg))
+              if (llvm::to_integer(key, reg))
                 expedited_register_map[reg] =
                     std::string(object->GetStringValue());
               return true; // Keep iterating through all array items