[CodeView Type Merging] Don't keep re-allocating temp serializer.

Previously, every time we wanted to serialize a field list record, we
would create a new copy of FieldListRecordBuilder, which would in turn
create a temporary instance of TypeSerializer, which itself had a
std::vector<> that was about 128K in size. So this 128K allocation was
happening every time. We can re-use the same instance over and over, we
just have to clear its internal hash table and seen records list between
each run. This saves us from the constant re-allocations.

This is worth an ~18.5% speed increase (3.75s -> 3.05s) in my tests.

Differential Revision: https://reviews.llvm.org/D33506

llvm-svn: 303919

2 files changed, 19 insertions, 9 deletions

diff --git a/llvm/lib/DebugInfo/CodeView/TypeSerializer.cpp b/llvm/lib/DebugInfo/CodeView/TypeSerializer.cpp
index 4894277947b..93c1198e36c 100644
--- a/llvm/lib/DebugInfo/CodeView/TypeSerializer.cpp
+++ b/llvm/lib/DebugInfo/CodeView/TypeSerializer.cpp
@@ -78,6 +78,8 @@ private:
 public:
   TypeHasher(BumpPtrAllocator &RecordStorage) : RecordStorage(RecordStorage) {}
 
+  void reset() { HashedRecords.clear(); }
+
   /// Takes the bytes of type record, inserts them into the hash table, saves
   /// them, and returns a pointer to an identical stable type record along with
   /// its type index in the destination stream.
@@ -172,6 +174,17 @@ ArrayRef<ArrayRef<uint8_t>> TypeSerializer::records() const {
   return SeenRecords;
 }
 
+void TypeSerializer::reset() {
+  if (Hasher)
+    Hasher->reset();
+  Writer.setOffset(0);
+  CurrentSegment = RecordSegment();
+  FieldListSegments.clear();
+  TypeKind.reset();
+  MemberKind.reset();
+  SeenRecords.clear();
+}
+
 TypeIndex TypeSerializer::insertRecordBytes(ArrayRef<uint8_t> &Record) {
   assert(!TypeKind.hasValue() && "Already in a type mapping!");
   assert(Writer.getOffset() == 0 && "Stream has data already!");
diff --git a/llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp b/llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
index 0f8357ca80f..c7f256b838a 100644
--- a/llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
+++ b/llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
@@ -490,21 +490,18 @@ Error TypeStreamMerger::visitKnownRecord(CVType &CVR, FieldListRecord &R) {
   assert(DestTypeStream);
   // Visit the members inside the field list.
   HadUntranslatedMember = false;
-  FieldListBuilder = llvm::make_unique<FieldListRecordBuilder>(*DestTypeStream);
+  if (!FieldListBuilder)
+    FieldListBuilder =
+        llvm::make_unique<FieldListRecordBuilder>(*DestTypeStream);
 
   FieldListBuilder->begin();
   if (auto EC = codeview::visitMemberRecordStream(CVR.content(), *this))
     return EC;
 
   // Write the record if we translated all field list members.
-  TypeIndex DestIdx = Untranslated;
-  if (!HadUntranslatedMember)
-    DestIdx = FieldListBuilder->end();
-  else
-    FieldListBuilder->reset();
-  addMapping(DestIdx);
-
-  FieldListBuilder.reset();
+  TypeIndex DestIdx = FieldListBuilder->end(!HadUntranslatedMember);
+  addMapping(HadUntranslatedMember ? Untranslated : DestIdx);
+
   return Error::success();
 }