[Clang][Type] Add static assertion to guard future expansion for BuiltinType numbering

Recent expansion D152070 exceeds the limit and I had a hard time
triaging the bug because the overflow just creates unexpected
behaviors within the compiler.

This patch adds a static assertion to keep an eye for overflows when we
expand more types in the future.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D152429

diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
index 87e69bf61a8e0714a0ec238a604ea962c352b8fa..49ea77429e7a1aef26ce8be50cd0474fffdbca15 100644 (file)
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -1649,7 +1649,8 @@ protected:
     unsigned : NumTypeBits;
 
     /// The kind (BuiltinType::Kind) of builtin type this is.
-    unsigned Kind : 8;
+    static constexpr unsigned NumOfBuiltinTypeBits = 8;
+    unsigned Kind : NumOfBuiltinTypeBits;
   };
 
   /// FunctionTypeBitfields store various bits belonging to FunctionProtoType.
@@ -2677,6 +2678,10 @@ private:
       : Type(Builtin, QualType(),
              K == Dependent ? TypeDependence::DependentInstantiation
                             : TypeDependence::None) {
+    static_assert(Kind::LastKind <
+                      (1 << BuiltinTypeBitfields::NumOfBuiltinTypeBits) &&
+                  "Defined builtin type exceeds the allocated space for serial "
+                  "numbering");
     BuiltinTypeBits.Kind = K;
   }