[C2x][ObjC] Do not crash when trying to encode a _BitInt type

[aaron.ballman]

Summary

Using a _BitInt (or _ExtInt) type as a block parameter or block return type hits an "unreachable" when trying to determine the encoding for the block. Instead of crashing, this patch handles it like some of the other types for which we don't yet have an encoding. The test case verifies we no longer crash, but does not verify that we provide any particular encoding (it can be updated once someone more familiar with ObjC steps in to define the encoding).

Fixes PR50503.

[erichkeane]

These seems right to me, but I think @rjmccall knows more about ObjC to make sure nothing silly is happening here.

[rjmccall]

I don't think you really need the FIXME when we don't have it for all the other types that we don't have encodings for.

[rjmccall]

But overall this seems fine, yeah.

[aaron.ballman]

Thanks for the reviews! I've landed in b6d9ca14c20f6f982a9fee4bebccf4761400f6aa (with the FIXME removed). Self-accepting on the two LGs so that I can close the review.

clang/lib/AST/ASTContext.cpp

       *NotEncodedT = T;
     return;
 
   case Type::ConstantMatrix:
     if (NotEncodedT)
       *NotEncodedT = T;
     return;
 
+  // FIXME: We should do better than this, but this is better than crashing.
+  case Type::BitInt:
+    if (NotEncodedT)
+      *NotEncodedT = T;
+    return;
+
   // We could see an undeduced auto type here during error recovery.
   // Just ignore it.
   case Type::Auto:
   case Type::DeducedTemplateSpecialization:
     return;
 
   case Type::Pipe:
-  case Type::BitInt:
 #define ABSTRACT_TYPE(KIND, BASE)
 #define TYPE(KIND, BASE)
 #define DEPENDENT_TYPE(KIND, BASE) \
   case Type::KIND:
 #define NON_CANONICAL_TYPE(KIND, BASE) \
   case Type::KIND:
 #define NON_CANONICAL_UNLESS_DEPENDENT_TYPE(KIND, BASE) \
   case Type::KIND:

clang/test/CodeGenObjC/encode-test-bitint.m

+// RUN: %clang_cc1 -triple i686-apple-darwin9 -fobjc-runtime=macosx-fragile-10.5 -fblocks -emit-llvm -o /dev/null %s
+
+// Using a _BitInt as a block parameter or return type previously would crash
+// when getting the ObjC encoding for the type. Verify that we no longer crash,
+// but do not verify any particular encoding (one has not yet been determined).
+void foo1(void)
+{
+    __auto_type blk = ^int(unsigned _BitInt(64) len)
+    {
+        return 12;
+    };
+}
+
+void foo2(void)
+{
+    __auto_type blk = ^unsigned _BitInt(64)(int len)
+    {
+        return 12;
+    };
+}
+