[Sema] Implement __make_integer_seq

This new builtin template allows for incredibly fast instantiations of
templates like std::integer_sequence.

Performance numbers follow:
My work station has 64 GB of ram + 20 Xeon Cores at 2.8 GHz.

__make_integer_seq<std::integer_sequence, int, 90000> takes 0.25
seconds.

std::make_integer_sequence<int, 90000> takes unbound time, it is still
running.  Clang is consuming gigabytes of memory.

Differential Revision: http://reviews.llvm.org/D13786

llvm-svn: 252036

4 files changed, 11 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTCommon.cpp b/clang/lib/Serialization/ASTCommon.cpp
index ec1a936684f..2b78d745864 100644
--- a/clang/lib/Serialization/ASTCommon.cpp
+++ b/clang/lib/Serialization/ASTCommon.cpp
@@ -329,6 +329,7 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::ClassScopeFunctionSpecialization:
   case Decl::Import:
   case Decl::OMPThreadPrivate:
+  case Decl::BuiltinTemplate:
     return false;
 
   // These indirectly derive from Redeclarable<T> but are not actually
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index c09e97c1584..b7b56f68b81 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -6412,6 +6412,9 @@ static Decl *getPredefinedDecl(ASTContext &Context, PredefinedDeclIDs ID) {
 
   case PREDEF_DECL_EXTERN_C_CONTEXT_ID:
     return Context.getExternCContextDecl();
+
+  case PREDEF_DECL_MAKE_INTEGER_SEQ_ID:
+    return Context.getMakeIntegerSeqDecl();
   }
   llvm_unreachable("PredefinedDeclIDs unknown enum value");
 }
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 50ef36ef634..317846c7a4f 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -293,6 +293,7 @@ namespace clang {
     DeclID VisitTemplateDecl(TemplateDecl *D);
     RedeclarableResult VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D);
     void VisitClassTemplateDecl(ClassTemplateDecl *D);
+    void VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D);
     void VisitVarTemplateDecl(VarTemplateDecl *D);
     void VisitFunctionTemplateDecl(FunctionTemplateDecl *D);
     void VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
@@ -1856,6 +1857,10 @@ void ASTDeclReader::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   }
 }
 
+void ASTDeclReader::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
+  llvm_unreachable("BuiltinTemplates are not serialized");
+}
+
 /// TODO: Unify with ClassTemplateDecl version?
 ///       May require unifying ClassTemplateDecl and
 ///        VarTemplateDecl beyond TemplateDecl...
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index c5a9755fed3..8fc32eaaa93 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -4136,6 +4136,8 @@ uint64_t ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
   RegisterPredefDecl(Context.BuiltinMSVaListDecl,
                      PREDEF_DECL_BUILTIN_MS_VA_LIST_ID);
   RegisterPredefDecl(Context.ExternCContext, PREDEF_DECL_EXTERN_C_CONTEXT_ID);
+  RegisterPredefDecl(Context.MakeIntegerSeqDecl,
+                     PREDEF_DECL_MAKE_INTEGER_SEQ_ID);
 
   // Build a record containing all of the tentative definitions in this file, in
   // TentativeDefinitions order.  Generally, this record will be empty for