[PATCH] Keep track of canonical decls in Redeclarable.

[Manuel Klimek]

Hi rsmith,

More than 2x speedup on modules builds with large redecl chains.
Between 2-3% cost in memory on large TUs.

http://reviews.llvm.org/D8619

Files:
  include/clang/AST/Decl.h
  include/clang/AST/Redeclarable.h
  lib/Serialization/ASTReaderDecl.cpp

Index: include/clang/AST/Decl.h
===================================================================
--- include/clang/AST/Decl.h
+++ include/clang/AST/Decl.h
@@ -3738,8 +3738,6 @@
   assert(RedeclLink.NextIsLatest() &&
          "setPreviousDecl on a decl already in a redeclaration chain");
 
-  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
Index: include/clang/AST/Redeclarable.h
===================================================================
--- include/clang/AST/Redeclarable.h
+++ include/clang/AST/Redeclarable.h
@@ -121,14 +121,15 @@
   ///
   /// If there is only one declaration, it is <pointer to self, true>
   DeclLink RedeclLink;
+  decl_type *First;
 
   decl_type *getNextRedeclaration() const {
     return RedeclLink.getNext(static_cast<const decl_type *>(this));
   }
 
 public:
-  Redeclarable(const ASTContext &Ctx)
-      : RedeclLink(LatestDeclLink(Ctx)) {}
+ Redeclarable(const ASTContext &Ctx)
+     : RedeclLink(LatestDeclLink(Ctx)), First(static_cast<decl_type *>(this)) {}
 
   /// \brief Return the previous declaration of this declaration or NULL if this
   /// is the first declaration.
@@ -144,21 +145,11 @@
 
   /// \brief Return the first declaration of this declaration or itself if this
   /// is the only declaration.
-  decl_type *getFirstDecl() {
-    decl_type *D = static_cast<decl_type*>(this);
-    while (D->getPreviousDecl())
-      D = D->getPreviousDecl();
-    return D;
-  }
+  decl_type *getFirstDecl() { return First; }
 
   /// \brief Return the first declaration of this declaration or itself if this
   /// is the only declaration.
-  const decl_type *getFirstDecl() const {
-    const decl_type *D = static_cast<const decl_type*>(this);
-    while (D->getPreviousDecl())
-      D = D->getPreviousDecl();
-    return D;
-  }
+  const decl_type *getFirstDecl() const { return First; }
 
   /// \brief True if this is the first declaration in its redeclaration chain.
   bool isFirstDecl() const { return RedeclLink.NextIsLatest(); }
Index: lib/Serialization/ASTReaderDecl.cpp
===================================================================
--- lib/Serialization/ASTReaderDecl.cpp
+++ lib/Serialization/ASTReaderDecl.cpp
@@ -2106,6 +2106,7 @@
     // which is the one that matters and mark the real previous DeclID to be
     // loaded & attached later on.
     D->RedeclLink = Redeclarable<T>::PreviousDeclLink(FirstDecl);
+    D->First = FirstDecl->getCanonicalDecl();
   }    
   
   // Note that this declaration has been deserialized.
@@ -2209,6 +2210,7 @@
     // of the existing declaration, so that this declaration has the
     // appropriate canonical declaration.
     D->RedeclLink = Redeclarable<T>::PreviousDeclLink(ExistingCanon);
+    D->First = ExistingCanon;
 
     // When we merge a namespace, update its pointer to the first namespace.
     // We cannot have loaded any redeclarations of this declaration yet, so
@@ -2828,6 +2830,7 @@
                                            Redeclarable<DeclT> *D,
                                            Decl *Previous, Decl *Canon) {
   D->RedeclLink.setPrevious(cast<DeclT>(Previous));
+  D->First = cast<DeclT>(Previous)->First;
 }
 namespace clang {
 template<>
@@ -2838,6 +2841,7 @@
   FunctionDecl *PrevFD = cast<FunctionDecl>(Previous);
 
   FD->RedeclLink.setPrevious(PrevFD);
+  FD->First = PrevFD->First;
 
   // If the previous declaration is an inline function declaration, then this
   // declaration is too.

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