diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -5581,6 +5581,9 @@
   ExprResult ActOnAsTypeExpr(Expr *E, ParsedType ParsedDestTy,
                              SourceLocation BuiltinLoc,
                              SourceLocation RParenLoc);
+  ExprResult BuildAsTypeExpr(Expr *E, QualType DestTy,
+                             SourceLocation BuiltinLoc,
+                             SourceLocation RParenLoc);
 
   //===---------------------------- C++ Features --------------------------===//
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6497,24 +6497,30 @@
                                ExecConfig, IsExecConfig);
 }
 
-/// ActOnAsTypeExpr - create a new asType (bitcast) from the arguments.
+/// Parse a __builtin_astype expression.
 ///
 /// __builtin_astype( value, dst type )
 ///
 ExprResult Sema::ActOnAsTypeExpr(Expr *E, ParsedType ParsedDestTy,
                                  SourceLocation BuiltinLoc,
                                  SourceLocation RParenLoc) {
+  QualType DstTy = GetTypeFromParser(ParsedDestTy);
+  return BuildAsTypeExpr(E, DstTy, BuiltinLoc, RParenLoc);
+}
+
+/// Create a new AsTypeExpr node (bitcast) from the arguments.
+ExprResult Sema::BuildAsTypeExpr(Expr *E, QualType DestTy,
+                                 SourceLocation BuiltinLoc,
+                                 SourceLocation RParenLoc) {
   ExprValueKind VK = VK_RValue;
   ExprObjectKind OK = OK_Ordinary;
-  QualType DstTy = GetTypeFromParser(ParsedDestTy);
   QualType SrcTy = E->getType();
-  if (Context.getTypeSize(DstTy) != Context.getTypeSize(SrcTy))
-    return ExprError(Diag(BuiltinLoc,
-                          diag::err_invalid_astype_of_different_size)
-                     << DstTy
-                     << SrcTy
-                     << E->getSourceRange());
-  return new (Context) AsTypeExpr(E, DstTy, VK, OK, BuiltinLoc, RParenLoc);
+  if (!SrcTy->isDependentType() &&
+      Context.getTypeSize(DestTy) != Context.getTypeSize(SrcTy))
+    return ExprError(
+        Diag(BuiltinLoc, diag::err_invalid_astype_of_different_size)
+        << DestTy << SrcTy << E->getSourceRange());
+  return new (Context) AsTypeExpr(E, DestTy, VK, OK, BuiltinLoc, RParenLoc);
 }
 
 /// ActOnConvertVectorExpr - create a new convert-vector expression from the
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -13971,7 +13971,14 @@
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformAsTypeExpr(AsTypeExpr *E) {
-  llvm_unreachable("Cannot transform asType expressions yet");
+  ExprResult SrcExpr = getDerived().TransformExpr(E->getSrcExpr());
+  if (SrcExpr.isInvalid())
+    return ExprError();
+
+  QualType Type = getDerived().TransformType(E->getType());
+
+  return SemaRef.BuildAsTypeExpr(SrcExpr.get(), Type, E->getBuiltinLoc(),
+                                 E->getRParenLoc());
 }
 
 template<typename Derived>
diff --git a/clang/test/SemaOpenCLCXX/template-astype.cl b/clang/test/SemaOpenCLCXX/template-astype.cl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaOpenCLCXX/template-astype.cl
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -fdeclare-opencl-builtins -finclude-default-header %s -cl-std=clc++ -verify
+
+// Test as_type, which is defined in terms of __builtin_astype.
+template <typename T>
+auto templated_astype(T x) {
+  return as_int2(x);
+  // expected-error@-1{{invalid reinterpretation: sizes of 'int2' (vector of 2 'int' values) and '__private int' must match}}
+}
+
+auto test_long(long x) { return templated_astype(x); }
+
+auto neg_test_int(int x) { return templated_astype(x); }
+// expected-note@-1{{in instantiation of function template specialization 'templated_astype<int>' requested here}}
+
+auto test_short4(short4 x) { return templated_astype(x); }
+
+// Test __builtin_astype.
+template <typename T>
+auto templated_builtin_astype(T x) {
+  return __builtin_astype(x, int2);
+}
+
+auto test_builtin(char8 x) { return templated_builtin_astype(x); }