Re-implement caching for the linkage calculation of declarations.

My previous attempt at solving the compile-time problem with many
redeclarations of the same entity cached both linkage and visibility,
while this patch only tackles linkage. There are several reasons for
this difference:

  - Linkage is a language concept, and is evaluated many times during
    semantic analysis and codegen, while visibility is only a
    code-generation concept that is evaluated only once per (unique)
    declaration. Hence, we *must* optimize linkage calculations but
    don't need to optimize visibility computation.
  - Once we know the linkage of a declaration, subsequent
    redeclarations can't change that linkage. Hence, cache
    invalidation is far simpler than for visibility, where a later
    redeclaration can completely change the visibility.
  - We have 3 spare bits in Decl to store the linkage cache, so the
    cache doesn't increase the size of declarations. With the
    visibility+linkage cache, NamedDecl got larger.

llvm-svn: 121023

5 files changed, 140 insertions, 65 deletions

diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index bdc91a168ee..299d5f6f4e4 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -264,7 +264,7 @@ public:
   };
 
   /// \brief Determine what kind of linkage this entity has.
-  Linkage getLinkage() const { return getLinkageAndVisibility().linkage(); }
+  Linkage getLinkage() const;
 
   /// \brief Determines the visibility of this entity.
   Visibility getVisibility() const { return getLinkageAndVisibility().visibility(); }
@@ -272,6 +272,10 @@ public:
   /// \brief Determines the linkage and visibility of this entity.
   LinkageInfo getLinkageAndVisibility() const;
 
+  /// \brief Clear the linkage cache in response to a change
+  /// to the declaration. 
+  void ClearLinkageCache() { HasCachedLinkage = 0; }
+
   /// \brief Looks through UsingDecls and ObjCCompatibleAliasDecls for
   /// the underlying named decl.
   NamedDecl *getUnderlyingDecl();
@@ -625,6 +629,8 @@ private:
   bool NRVOVariable : 1;
   
   friend class StmtIteratorBase;
+  friend class ASTDeclReader;
+  
 protected:
   VarDecl(Kind DK, DeclContext *DC, SourceLocation L, IdentifierInfo *Id,
           QualType T, TypeSourceInfo *TInfo, StorageClass SC,
@@ -660,10 +666,7 @@ public:
   StorageClass getStorageClassAsWritten() const {
     return (StorageClass) SClassAsWritten;
   }
-  void setStorageClass(StorageClass SC) {
-    assert(isLegalForVariable(SC));
-    SClass = SC;
-  }
+  void setStorageClass(StorageClass SC);
   void setStorageClassAsWritten(StorageClass SC) {
     assert(isLegalForVariable(SC));
     SClassAsWritten = SC;
@@ -1478,10 +1481,7 @@ public:
   }
                        
   StorageClass getStorageClass() const { return StorageClass(SClass); }
-  void setStorageClass(StorageClass SC) {
-    assert(isLegalForFunction(SC));
-    SClass = SC;
-  }
+  void setStorageClass(StorageClass SC);
 
   StorageClass getStorageClassAsWritten() const {
     return StorageClass(SClassAsWritten);
@@ -2558,6 +2558,32 @@ inline const DiagnosticBuilder &operator<<(const DiagnosticBuilder &DB,
   return DB;
 }
 
+template<typename decl_type>
+void Redeclarable<decl_type>::setPreviousDeclaration(decl_type *PrevDecl) {
+  // Note: This routine is implemented here because we need both NamedDecl
+  // and Redeclarable to be defined.
+
+  decl_type *First;
+  
+  if (PrevDecl) {
+    // Point to previous. Make sure that this is actually the most recent
+    // redeclaration, or we can build invalid chains. If the most recent
+    // redeclaration is invalid, it won't be PrevDecl, but we want it anyway.
+    RedeclLink = PreviousDeclLink(llvm::cast<decl_type>(
+                                                        PrevDecl->getMostRecentDeclaration()));
+    First = PrevDecl->getFirstDeclaration();
+    assert(First->RedeclLink.NextIsLatest() && "Expected first");
+  } else {
+    // Make this first.
+    First = static_cast<decl_type*>(this);
+  }
+  
+  // First one will point to this one as latest.
+  First->RedeclLink = LatestDeclLink(static_cast<decl_type*>(this));
+  if (NamedDecl *ND = dyn_cast<NamedDecl>(static_cast<decl_type*>(this)))
+    ND->ClearLinkageCache();
+}
+
 }  // end namespace clang
 
 #endif
diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
index 0aa60ce9782..f091ce043ad 100644
--- a/clang/include/clang/AST/DeclBase.h
+++ b/clang/include/clang/AST/DeclBase.h
@@ -198,7 +198,7 @@ private:
     return DeclCtx.get<DeclContext*>();
   }
 
-  /// Loc - The location that this decl.
+  /// Loc - The location of this decl.
   SourceLocation Loc;
 
   /// DeclKind - This indicates which class this is.
@@ -231,8 +231,19 @@ protected:
   unsigned ChangedAfterLoad : 1;
 
   /// IdentifierNamespace - This specifies what IDNS_* namespace this lives in.
-  unsigned IdentifierNamespace : 15;
+  unsigned IdentifierNamespace : 12;
 
+  /// \brief Whether the \c CachedLinkage field is active.
+  ///
+  /// This field is only valid for NamedDecls subclasses.
+  mutable unsigned HasCachedLinkage : 1;
+  
+  /// \brief If \c HasCachedLinkage, the linkage of this declaration.
+  ///
+  /// This field is only valid for NamedDecls subclasses.
+  mutable unsigned CachedLinkage : 2;
+  
+  
 private:
   void CheckAccessDeclContext() const;
 
@@ -243,7 +254,9 @@ protected:
       Loc(L), DeclKind(DK), InvalidDecl(0),
       HasAttrs(false), Implicit(false), Used(false),
       Access(AS_none), PCHLevel(0), ChangedAfterLoad(false),
-      IdentifierNamespace(getIdentifierNamespaceForKind(DK)) {
+      IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
+      HasCachedLinkage(0) 
+  {
     if (Decl::CollectingStats()) add(DK);
   }
 
@@ -251,7 +264,9 @@ protected:
     : NextDeclInContext(0), DeclKind(DK), InvalidDecl(0),
       HasAttrs(false), Implicit(false), Used(false),
       Access(AS_none), PCHLevel(0), ChangedAfterLoad(false),
-      IdentifierNamespace(getIdentifierNamespaceForKind(DK)) {
+      IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
+      HasCachedLinkage(0)
+  {
     if (Decl::CollectingStats()) add(DK);
   }
 
diff --git a/clang/include/clang/AST/Redeclarable.h b/clang/include/clang/AST/Redeclarable.h
index ba778293ba2..e87ca78d635 100644
--- a/clang/include/clang/AST/Redeclarable.h
+++ b/clang/include/clang/AST/Redeclarable.h
@@ -109,25 +109,7 @@ public:
   
   /// \brief Set the previous declaration. If PrevDecl is NULL, set this as the
   /// first and only declaration.
-  void setPreviousDeclaration(decl_type *PrevDecl) {
-    decl_type *First;
-
-    if (PrevDecl) {
-      // Point to previous. Make sure that this is actually the most recent
-      // redeclaration, or we can build invalid chains. If the most recent
-      // redeclaration is invalid, it won't be PrevDecl, but we want it anyway.
-      RedeclLink = PreviousDeclLink(llvm::cast<decl_type>(
-                                      PrevDecl->getMostRecentDeclaration()));
-      First = PrevDecl->getFirstDeclaration();
-      assert(First->RedeclLink.NextIsLatest() && "Expected first");
-    } else {
-      // Make this first.
-      First = static_cast<decl_type*>(this);
-    }
-
-    // First one will point to this one as latest.
-    First->RedeclLink = LatestDeclLink(static_cast<decl_type*>(this));
-  }
+  void setPreviousDeclaration(decl_type *PrevDecl);
 
   /// \brief Iterates through all the redeclarations of the same decl.
   class redecl_iterator {
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 71bda4156f9..90a561e5c6e 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -85,6 +85,15 @@ struct LVFlags {
               ConsiderVisibilityAttributes(true) {
   }
 
+  /// \brief Returns a set of flags that is only useful for computing the 
+  /// linkage, not the visibility, of a declaration.
+  static LVFlags CreateOnlyDeclLinkage() {
+    LVFlags F;
+    F.ConsiderGlobalVisibility = false;
+    F.ConsiderVisibilityAttributes = false;
+    return F;
+  }
+  
   /// Returns a set of flags, otherwise based on these, which ignores
   /// off all sources of visibility except template arguments.
   LVFlags onlyTemplateVisibility() const {
@@ -119,10 +128,14 @@ getLVForTemplateParameterList(const TemplateParameterList *Params) {
   return LV;
 }
 
+/// getLVForDecl - Get the linkage and visibility for the given declaration.
+static LinkageInfo getLVForDecl(const NamedDecl *D, LVFlags F);
+
 /// \brief Get the most restrictive linkage for the types and
 /// declarations in the given template argument list.
 static LVPair getLVForTemplateArgumentList(const TemplateArgument *Args,
-                                           unsigned NumArgs) {
+                                           unsigned NumArgs,
+                                           LVFlags &F) {
   LVPair LV(ExternalLinkage, DefaultVisibility);
 
   for (unsigned I = 0; I != NumArgs; ++I) {
@@ -140,21 +153,24 @@ static LVPair getLVForTemplateArgumentList(const TemplateArgument *Args,
       // The decl can validly be null as the representation of nullptr
       // arguments, valid only in C++0x.
       if (Decl *D = Args[I].getAsDecl()) {
-        if (NamedDecl *ND = dyn_cast<NamedDecl>(D))
-          LV = merge(LV, ND->getLinkageAndVisibility());
-        if (ValueDecl *VD = dyn_cast<ValueDecl>(D))
-          LV = merge(LV, VD->getLinkageAndVisibility());
+        if (NamedDecl *ND = dyn_cast<NamedDecl>(D)) {
+          LinkageInfo LI = getLVForDecl(ND, F);
+          LV = merge(LV, LVPair(LI.linkage(), LI.visibility()));
+        }
       }
       break;
 
     case TemplateArgument::Template:
-      if (TemplateDecl *Template = Args[I].getAsTemplate().getAsTemplateDecl())
-        LV = merge(LV, Template->getLinkageAndVisibility());
+      if (TemplateDecl *Template = Args[I].getAsTemplate().getAsTemplateDecl()){
+        LinkageInfo LI = getLVForDecl(Template, F);
+        LV = merge(LV, LVPair(LI.linkage(), LI.visibility()));
+      }
       break;
 
     case TemplateArgument::Pack:
       LV = merge(LV, getLVForTemplateArgumentList(Args[I].pack_begin(),
-                                                  Args[I].pack_size()));
+                                                  Args[I].pack_size(),
+                                                  F));
       break;
     }
   }
@@ -163,14 +179,11 @@ static LVPair getLVForTemplateArgumentList(const TemplateArgument *Args,
 }
 
 static LVPair
-getLVForTemplateArgumentList(const TemplateArgumentList &TArgs) {
-  return getLVForTemplateArgumentList(TArgs.data(), TArgs.size());
+getLVForTemplateArgumentList(const TemplateArgumentList &TArgs,
+                             LVFlags &F) {
+  return getLVForTemplateArgumentList(TArgs.data(), TArgs.size(), F);
 }
 
-/// getLVForDecl - Get the cached linkage and visibility for the given
-/// declaration.
-static LinkageInfo getLVForDecl(const NamedDecl *D, LVFlags F);
-
 static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
   assert(D->getDeclContext()->getRedeclContext()->isFileContext() &&
          "Not a name having namespace scope");
@@ -296,7 +309,7 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
       //   is visible, or if the prior declaration specifies no
       //   linkage, then the identifier has external linkage.
       if (const VarDecl *PrevVar = Var->getPreviousDeclaration()) {
-        LinkageInfo PrevLV = PrevVar->getLinkageAndVisibility();
+        LinkageInfo PrevLV = getLVForDecl(PrevVar, F);
         if (PrevLV.linkage()) LV.setLinkage(PrevLV.linkage());
         LV.mergeVisibility(PrevLV);
       }
@@ -331,7 +344,7 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
       //   is visible, or if the prior declaration specifies no
       //   linkage, then the identifier has external linkage.
       if (const FunctionDecl *PrevFunc = Function->getPreviousDeclaration()) {
-        LinkageInfo PrevLV = PrevFunc->getLinkageAndVisibility();
+        LinkageInfo PrevLV = getLVForDecl(PrevFunc, F);
         if (PrevLV.linkage()) LV.setLinkage(PrevLV.linkage());
         LV.mergeVisibility(PrevLV);
       }
@@ -342,7 +355,7 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
       LV.merge(getLVForDecl(SpecInfo->getTemplate(),
                             F.onlyTemplateVisibility()));
       const TemplateArgumentList &TemplateArgs = *SpecInfo->TemplateArguments;
-      LV.merge(getLVForTemplateArgumentList(TemplateArgs));
+      LV.merge(getLVForTemplateArgumentList(TemplateArgs, F));
     }
 
   //     - a named class (Clause 9), or an unnamed class defined in a
@@ -366,7 +379,7 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
 
       // The arguments at which the template was instantiated.
       const TemplateArgumentList &TemplateArgs = Spec->getTemplateArgs();
-      LV.merge(getLVForTemplateArgumentList(TemplateArgs));
+      LV.merge(getLVForTemplateArgumentList(TemplateArgs, F));
     }
 
     // Consider -fvisibility unless the type has C linkage.
@@ -377,8 +390,7 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D, LVFlags F) {
 
   //     - an enumerator belonging to an enumeration with external linkage;
   } else if (isa<EnumConstantDecl>(D)) {
-    LinkageInfo EnumLV =
-      cast<NamedDecl>(D->getDeclContext())->getLinkageAndVisibility();
+    LinkageInfo EnumLV = getLVForDecl(cast<NamedDecl>(D->getDeclContext()), F);
     if (!isExternalLinkage(EnumLV.linkage()))
       return LinkageInfo::none();
     LV.merge(EnumLV);
@@ -464,7 +476,7 @@ static LinkageInfo getLVForClassMember(const NamedDecl *D, LVFlags F) {
     // the template parameters and arguments.
     if (FunctionTemplateSpecializationInfo *Spec
            = MD->getTemplateSpecializationInfo()) {
-      LV.merge(getLVForTemplateArgumentList(*Spec->TemplateArguments));
+      LV.merge(getLVForTemplateArgumentList(*Spec->TemplateArguments, F));
       LV.merge(getLVForTemplateParameterList(
                               Spec->getTemplate()->getTemplateParameters()));
 
@@ -499,7 +511,7 @@ static LinkageInfo getLVForClassMember(const NamedDecl *D, LVFlags F) {
         = dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
       // Merge template argument/parameter information for member
       // class template specializations.
-      LV.merge(getLVForTemplateArgumentList(Spec->getTemplateArgs()));
+      LV.merge(getLVForTemplateArgumentList(Spec->getTemplateArgs(), F));
       LV.merge(getLVForTemplateParameterList(
                     Spec->getSpecializedTemplate()->getTemplateParameters()));
     }
@@ -525,8 +537,27 @@ static LinkageInfo getLVForClassMember(const NamedDecl *D, LVFlags F) {
   return LV;
 }
 
+Linkage NamedDecl::getLinkage() const {
+  if (HasCachedLinkage) {
+#ifndef NDEBUG
+    assert(CachedLinkage == getLVForDecl(this, 
+                                  LVFlags::CreateOnlyDeclLinkage()).linkage());
+#endif
+    return Linkage(CachedLinkage);
+  }
+
+  CachedLinkage = getLVForDecl(this, 
+                               LVFlags::CreateOnlyDeclLinkage()).linkage();
+  HasCachedLinkage = 1;
+  return Linkage(CachedLinkage);
+}
+
 LinkageInfo NamedDecl::getLinkageAndVisibility() const {
-  return getLVForDecl(this, LVFlags());
+  LinkageInfo LI = getLVForDecl(this, LVFlags());
+  assert(!HasCachedLinkage || (CachedLinkage == LI.linkage()));
+  HasCachedLinkage = 1;
+  CachedLinkage = LI.linkage();
+  return LI;
 }
 
 static LinkageInfo getLVForDecl(const NamedDecl *D, LVFlags Flags) {
@@ -581,11 +612,13 @@ static LinkageInfo getLVForDecl(const NamedDecl *D, LVFlags Flags) {
         return LinkageInfo::uniqueExternal();
 
       LinkageInfo LV;
-      if (const VisibilityAttr *VA = GetExplicitVisibility(Function))
-        LV.setVisibility(GetVisibilityFromAttr(VA));
-
+      if (Flags.ConsiderVisibilityAttributes) {
+        if (const VisibilityAttr *VA = GetExplicitVisibility(Function))
+          LV.setVisibility(GetVisibilityFromAttr(VA));
+      }
+      
       if (const FunctionDecl *Prev = Function->getPreviousDeclaration()) {
-        LinkageInfo PrevLV = Prev->getLinkageAndVisibility();
+        LinkageInfo PrevLV = getLVForDecl(Prev, Flags);
         if (PrevLV.linkage()) LV.setLinkage(PrevLV.linkage());
         LV.mergeVisibility(PrevLV);
       }
@@ -602,11 +635,13 @@ static LinkageInfo getLVForDecl(const NamedDecl *D, LVFlags Flags) {
         LinkageInfo LV;
         if (Var->getStorageClass() == SC_PrivateExtern)
           LV.setVisibility(HiddenVisibility);
-        else if (const VisibilityAttr *VA = GetExplicitVisibility(Var))
-          LV.setVisibility(GetVisibilityFromAttr(VA));
-
+        else if (Flags.ConsiderVisibilityAttributes) {
+          if (const VisibilityAttr *VA = GetExplicitVisibility(Var))
+            LV.setVisibility(GetVisibilityFromAttr(VA));
+        }
+        
         if (const VarDecl *Prev = Var->getPreviousDeclaration()) {
-          LinkageInfo PrevLV = Prev->getLinkageAndVisibility();
+          LinkageInfo PrevLV = getLVForDecl(Prev, Flags);
           if (PrevLV.linkage()) LV.setLinkage(PrevLV.linkage());
           LV.mergeVisibility(PrevLV);
         }
@@ -878,6 +913,14 @@ VarDecl *VarDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
   return new (C) VarDecl(Var, DC, L, Id, T, TInfo, S, SCAsWritten);
 }
 
+void VarDecl::setStorageClass(StorageClass SC) {
+  assert(isLegalForVariable(SC));
+  if (getStorageClass() != SC)
+    ClearLinkageCache();
+  
+  SClass = SC;
+}
+
 SourceLocation VarDecl::getInnerLocStart() const {
   SourceLocation Start = getTypeSpecStartLoc();
   if (Start.isInvalid())
@@ -1277,6 +1320,14 @@ FunctionDecl *FunctionDecl::getCanonicalDecl() {
   return getFirstDeclaration();
 }
 
+void FunctionDecl::setStorageClass(StorageClass SC) {
+  assert(isLegalForFunction(SC));
+  if (getStorageClass() != SC)
+    ClearLinkageCache();
+  
+  SClass = SC;
+}
+
 /// \brief Returns a value indicating whether this function
 /// corresponds to a builtin function.
 ///
@@ -1787,6 +1838,7 @@ void TagDecl::setTypedefForAnonDecl(TypedefDecl *TDD) {
   TypedefDeclOrQualifier = TDD; 
   if (TypeForDecl)
     TypeForDecl->ClearLinkageCache();
+  ClearLinkageCache();
 }
 
 void TagDecl::startDefinition() {
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index adbf3bff3c3..7053f404e43 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -384,7 +384,7 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   // FunctionDecl's body is handled last at ASTDeclReader::Visit,
   // after everything else is read.
 
-  FD->setStorageClass((StorageClass)Record[Idx++]);
+  FD->SClass = (StorageClass)Record[Idx++];
   FD->setStorageClassAsWritten((StorageClass)Record[Idx++]);
   FD->setInlineSpecified(Record[Idx++]);
   FD->setVirtualAsWritten(Record[Idx++]);
@@ -651,7 +651,7 @@ void ASTDeclReader::VisitIndirectFieldDecl(IndirectFieldDecl *FD) {
 void ASTDeclReader::VisitVarDecl(VarDecl *VD) {
   VisitDeclaratorDecl(VD);
   VisitRedeclarable(VD);
-  VD->setStorageClass((StorageClass)Record[Idx++]);
+  VD->SClass = (StorageClass)Record[Idx++];
   VD->setStorageClassAsWritten((StorageClass)Record[Idx++]);
   VD->setThreadSpecified(Record[Idx++]);
   VD->setCXXDirectInitializer(Record[Idx++]);