[modules] Further simplification and speedup of redeclaration chain loading.

Instead of eagerly deserializing a list of DeclIDs when we load a module file
and doing a binary search to find the redeclarations of a decl, store a list of
redeclarations of each chain before the first declaration and load it directly.

llvm-svn: 245789

1 files changed, 35 insertions, 34 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index f4f39a8506b..00785aa1d05 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2156,6 +2156,8 @@ ASTDeclReader::VisitRedeclarable(Redeclarable<T> *D) {
   bool IsKeyDecl = ThisDeclID == FirstDeclID;
   bool IsFirstLocalDecl = false;
 
+  uint64_t RedeclOffset = 0;
+
   // 0 indicates that this declaration was the only declaration of its entity,
   // and is used for space optimization.
   if (FirstDeclID == 0) {
@@ -2175,6 +2177,8 @@ ASTDeclReader::VisitRedeclarable(Redeclarable<T> *D) {
     // declaration.
     for (unsigned I = 0; I != N - 1; ++I)
       MergeWith = ReadDecl(Record, Idx/*, MergeWith*/);
+
+    RedeclOffset = Record[Idx++];
   } else {
     // This declaration was not the first local declaration. Read the first
     // local declaration now, to trigger the import of other redeclarations.
@@ -2198,7 +2202,7 @@ ASTDeclReader::VisitRedeclarable(Redeclarable<T> *D) {
   // above; this ensures that the redeclaration chain is built in the correct
   // order.
   if (IsFirstLocalDecl)
-    Reader.PendingDeclChains.push_back(DAsT);
+    Reader.PendingDeclChains.push_back(std::make_pair(DAsT, RedeclOffset));
 
   return RedeclarableResult(FirstDeclID, MergeWith, IsKeyDecl);
 }
@@ -3393,43 +3397,40 @@ void ASTReader::loadDeclUpdateRecords(serialization::DeclID ID, Decl *D) {
   }
 }
 
-void ASTReader::loadPendingDeclChain(Decl *FirstLocal) {
-  ModuleFile &M = *getOwningModuleFile(FirstLocal);
-  DeclID LocalID =
-      mapGlobalIDToModuleFileGlobalID(M, FirstLocal->getGlobalID());
-  assert(LocalID && "looking for redecl chain in wrong module file");
-
-  // Perform a binary search to find the local redeclarations for this
-  // declaration (if any).
-  // FIXME: Just store an offset with the first declaration.
-  const LocalRedeclarationsInfo Compare = {LocalID, 0};
-  const LocalRedeclarationsInfo *Result = std::lower_bound(
-      M.RedeclarationsMap,
-      M.RedeclarationsMap + M.LocalNumRedeclarationsInMap, Compare);
+void ASTReader::loadPendingDeclChain(Decl *FirstLocal, uint64_t LocalOffset) {
+  // Attach FirstLocal to the end of the decl chain.
+  Decl *CanonDecl = FirstLocal->getCanonicalDecl();
+  if (FirstLocal != CanonDecl) {
+    Decl *PrevMostRecent = ASTDeclReader::getMostRecentDecl(CanonDecl);
+    ASTDeclReader::attachPreviousDecl(
+        *this, FirstLocal, PrevMostRecent ? PrevMostRecent : CanonDecl,
+        CanonDecl);
+  }
 
-  // Pull out the list of redeclarations.
-  SmallVector<Decl*, 4> Chain;
-  if (Result != M.RedeclarationsMap + M.LocalNumRedeclarationsInMap &&
-      Result->FirstID == LocalID) {
-    unsigned Offset = Result->Offset;
-    unsigned N = M.RedeclarationChains[Offset++];
-    for (unsigned I = 0; I != N; ++I)
-      Chain.push_back(GetLocalDecl(M, M.RedeclarationChains[Offset++]));
+  if (!LocalOffset) {
+    ASTDeclReader::attachLatestDecl(CanonDecl, FirstLocal);
+    return;
   }
-  Chain.push_back(FirstLocal);
 
-  // Hook up the chain.
-  //
-  // FIXME: We have three different dispatches on decl kind here; maybe
+  // Load the list of other redeclarations from this module file.
+  ModuleFile *M = getOwningModuleFile(FirstLocal);
+  assert(M && "imported decl from no module file");
+
+  llvm::BitstreamCursor &Cursor = M->DeclsCursor;
+  SavedStreamPosition SavedPosition(Cursor);
+  Cursor.JumpToBit(LocalOffset);
+
+  RecordData Record;
+  unsigned Code = Cursor.ReadCode();
+  unsigned RecCode = Cursor.readRecord(Code, Record);
+  (void)RecCode;
+  assert(RecCode == LOCAL_REDECLARATIONS && "expected LOCAL_REDECLARATIONS record!");
+
+  // FIXME: We have several different dispatches on decl kind here; maybe
   // we should instead generate one loop per kind and dispatch up-front?
-  Decl *CanonDecl = FirstLocal->getCanonicalDecl();
-  Decl *MostRecent = ASTDeclReader::getMostRecentDecl(CanonDecl);
-  if (!MostRecent)
-    MostRecent = CanonDecl;
-  for (unsigned I = 0, N = Chain.size(); I != N; ++I) {
-    auto *D = Chain[N - I - 1];
-    if (D == CanonDecl)
-      continue;
+  Decl *MostRecent = FirstLocal;
+  for (unsigned I = 0, N = Record.size(); I != N; ++I) {
+    auto *D = GetLocalDecl(*M, Record[N - I - 1]);
     ASTDeclReader::attachPreviousDecl(*this, D, MostRecent, CanonDecl);
     MostRecent = D;
   }