Move imported entities into DwarfCompilationUnit to speed up LTO linking.

Summary:
In particular, this CL speeds up the official Chrome linking with LTO by
1.8x.

See more details in https://crbug.com/542426

Reviewers: dblaikie

Subscribers: jevinskie

Differential Revision: http://reviews.llvm.org/D13918

llvm-svn: 251353

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -342,9 +342,9 @@ void DwarfCompileUnit::constructScopeDIE(
     // Skip imported directives in gmlt-like data.
     if (!includeMinimalInlineScopes()) {
       // There is no need to emit empty lexical block DIE.
-      for (const auto &E : DD->findImportedEntitiesForScope(DS))
+      for (const auto *IE : ImportedEntities[DS])
           Children.push_back(
-            constructImportedEntityDIE(cast<DIImportedEntity>(E.second)));
+              constructImportedEntityDIE(cast<DIImportedEntity>(IE)));
     }
 
     // If there are only other scopes as children, put them directly in the

lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

@@ -39,6 +39,12 @@ class DwarfCompileUnit : public DwarfUnit {
   /// The start of the unit within its section.
   MCSymbol *LabelBegin;
 
+  typedef llvm::SmallVector<const MDNode *, 8> ImportedEntityList;
+  typedef llvm::DenseMap<const MDNode *, ImportedEntityList>
+  ImportedEntityMap;
+
+  ImportedEntityMap ImportedEntities;
+
   /// GlobalNames - A map of globally visible named entities for this unit.
   StringMap<const DIE *> GlobalNames;
 
@@ -98,6 +104,10 @@ public:
 
   unsigned getOrCreateSourceID(StringRef FileName, StringRef DirName) override;
 
+  void addImportedEntity(const DIImportedEntity* IE) {
+    ImportedEntities[IE->getScope()].push_back(IE);
+  }
+
   /// addRange - Add an address range to the list of ranges for this unit.
   void addRange(RangeSpan Range);
 

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -489,12 +489,7 @@ void DwarfDebug::beginModule() {
     auto *CUNode = cast<DICompileUnit>(N);
     DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
     for (auto *IE : CUNode->getImportedEntities())
-      ScopesWithImportedEntities.push_back(std::make_pair(IE->getScope(), IE));
-    // Stable sort to preserve the order of appearance of imported entities.
-    // This is to avoid out-of-order processing of interdependent declarations
-    // within the same scope, e.g. { namespace A = base; namespace B = A; }
-    std::stable_sort(ScopesWithImportedEntities.begin(),
-                     ScopesWithImportedEntities.end(), less_first());
+      CU.addImportedEntity(IE);
     for (auto *GV : CUNode->getGlobalVariables())
       CU.getOrCreateGlobalVariableDIE(GV);
     for (auto *SP : CUNode->getSubprograms())

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -289,11 +289,6 @@ class DwarfDebug : public AsmPrinterHandler {
   /// Holders for the various debug information flags that we might need to
   /// have exposed. See accessor functions below for description.
 
-  /// Holder for imported entities.
-  typedef SmallVector<std::pair<const MDNode *, const MDNode *>, 32>
-  ImportedEntityMap;
-  ImportedEntityMap ScopesWithImportedEntities;
-
   /// Map from MDNodes for user-defined types to the type units that
   /// describe them.
   DenseMap<const MDNode *, const DwarfTypeUnit *> DwarfTypeUnits;
@@ -626,14 +621,6 @@ public:
 
   const MachineFunction *getCurrentFunction() const { return CurFn; }
 
-  iterator_range<ImportedEntityMap::const_iterator>
-  findImportedEntitiesForScope(const MDNode *Scope) const {
-    return make_range(std::equal_range(
-        ScopesWithImportedEntities.begin(), ScopesWithImportedEntities.end(),
-        std::pair<const MDNode *, const MDNode *>(Scope, nullptr),
-        less_first()));
-  }
-
   /// A helper function to check whether the DIE for a given Scope is
   /// going to be null.
   bool isLexicalScopeDIENull(LexicalScope *Scope);