Simplify, and improve the performance of, template instantiation for

declaration references. The key realization is that dependent Decls,
which actually require instantiation, can only refer to the current
instantiation or members thereof. And, since the current context
during instantiation contains all of those members of the current
instantiation, we can simply find the real instantiate that matches up
with the "current instantiation" template.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@72486 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 20 deletions

diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 41c1944b54..33eedcec38 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -671,8 +671,8 @@ static NamedDecl *findInstantiationOf(ASTContext &Ctx,
   return 0;
 }
 
-/// \brief Find the instantiation of the given declaration with the
-/// given template arguments.
+/// \brief Find the instantiation of the given declaration within the
+/// current instantiation.
 ///
 /// This routine is intended to be used when \p D is a declaration
 /// referenced from within a template, that needs to mapped into the
@@ -695,10 +695,9 @@ static NamedDecl *findInstantiationOf(ASTContext &Ctx,
 /// In the instantiation of X<int>::getKind(), we need to map the
 /// EnumConstantDecl for KnownValue (which refers to
 /// X<T>::<Kind>::KnownValue) to its instantiation
-/// (X<int>::<Kind>::KnownValue). InstantiateDeclRef() performs this
-/// mapping, given the template arguments 'int'.
-NamedDecl *
-Sema::InstantiateDeclRef(NamedDecl *D, const TemplateArgumentList &TemplateArgs) {
+/// (X<int>::<Kind>::KnownValue). InstantiateCurrentDeclRef() performs
+/// this mapping from within the instantiation of X<int>.
+NamedDecl * Sema::InstantiateCurrentDeclRef(NamedDecl *D) {
   DeclContext *ParentDC = D->getDeclContext();
   if (isa<ParmVarDecl>(D) || ParentDC->isFunctionOrMethod()) {
     // D is a local of some kind. Look into the map of local
@@ -707,7 +706,7 @@ Sema::InstantiateDeclRef(NamedDecl *D, const TemplateArgumentList &TemplateArgs)
   }
 
   if (NamedDecl *ParentDecl = dyn_cast<NamedDecl>(ParentDC)) {
-    ParentDecl = InstantiateDeclRef(ParentDecl, TemplateArgs);
+    ParentDecl = InstantiateCurrentDeclRef(ParentDecl);
     if (!ParentDecl)
       return 0;
 
@@ -740,20 +739,27 @@ Sema::InstantiateDeclRef(NamedDecl *D, const TemplateArgumentList &TemplateArgs)
     D = Result;
   }
 
-  // D itself might be a class template that we need to instantiate
-  // with the given template arguments.
   if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D))
-    if (ClassTemplateDecl *ClassTemplate = Record->getDescribedClassTemplate()) {
-      QualType InjectedClassName 
-        = ClassTemplate->getInjectedClassNameType(Context);
-      QualType InstantiatedType = InstantiateType(InjectedClassName,
-                                                  TemplateArgs,
-                                                  Record->getLocation(), 
-                                                  Record->getDeclName());
-      if (InstantiatedType.isNull())
-        return 0;
-      if (const RecordType *RT = InstantiatedType->getAsRecordType())
-        D = RT->getDecl();
+    if (ClassTemplateDecl *ClassTemplate 
+          = Record->getDescribedClassTemplate()) {
+      // When the declaration D was parsed, it referred to the current
+      // instantiation. Therefore, look through the current context,
+      // which contains actual instantiations, to find the
+      // instantiation of the "current instantiation" that D refers
+      // to. Alternatively, we could just instantiate the
+      // injected-class-name with the current template arguments, but
+      // such an instantiation is far more expensive.
+      for (DeclContext *DC = CurContext; !DC->isFileContext(); 
+           DC = DC->getParent()) {
+        if (ClassTemplateSpecializationDecl *Spec 
+              = dyn_cast<ClassTemplateSpecializationDecl>(DC))
+          if (Context.getCanonicalDecl(Spec->getSpecializedTemplate())
+              == Context.getCanonicalDecl(ClassTemplate))
+            return Spec;
+      }
+
+      assert(false && 
+             "Unable to find declaration for the current instantiation");
     }
 
   return D;