Modules: Optimize bitcode encoding of diagnostic state

Since bitcode uses VBR encoding, large numbers are more expensive than
small ones.  Instead of emitting a UINT_MAX sentinel after each sequence
of state-change pairs, emit the size of the sequence as a prefix.

This should have no functionality change besides saving bits from the
encoding.

llvm-svn: 297770

2 files changed, 10 insertions, 6 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index be0cc9ab1a8..e4eddaef989 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5463,16 +5463,16 @@ void ASTReader::ReadPragmaDiagnosticMappings(DiagnosticsEngine &Diag) {
       Diag.DiagStates.push_back(BasedOn);
       DiagState *NewState = &Diag.DiagStates.back();
       DiagStates.push_back(NewState);
-      while (Idx + 1 < Record.size() && Record[Idx] != unsigned(-1)) {
+      unsigned Size = Record[Idx++];
+      assert(Idx + Size * 2 <= Record.size() &&
+             "Invalid data, not enough diag/map pairs");
+      while (Size--) {
         unsigned DiagID = Record[Idx++];
         diag::Severity Map = (diag::Severity)Record[Idx++];
         DiagnosticMapping Mapping = Diag.makeUserMapping(Map, Loc);
         if (Mapping.isPragma() || IncludeNonPragmaStates)
           NewState->setMapping(DiagID, Mapping);
       }
-      assert(Idx != Record.size() && Record[Idx] == unsigned(-1) &&
-             "Invalid data, didn't find '-1' marking end of diag/map pairs");
-      ++Idx;
       return NewState;
     };
 
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index b13a4e1ff4b..e9e64c2a66f 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -2871,14 +2871,18 @@ void ASTWriter::WritePragmaDiagnosticMappings(const DiagnosticsEngine &Diag,
   
     if (DiagStateID == 0) {
       DiagStateID = ++CurrID;
+
+      // Add a placeholder for the number of mappings.
+      auto SizeIdx = Record.size();
+      Record.emplace_back();
       for (const auto &I : *State) {
         if (I.second.isPragma() || IncludeNonPragmaStates) {
           Record.push_back(I.first);
           Record.push_back((unsigned)I.second.getSeverity());
         }
       }
-      // Add a sentinel to mark the end of the diag IDs.
-      Record.push_back(unsigned(-1));
+      // Update the placeholder.
+      Record[SizeIdx] = (Record.size() - SizeIdx) / 2;
     }
   };