[clang] [clang]Implement the c23 stdc bit builtins (PR #185978)

[Eli Friedman via cfe-commits]

================
@@ -3811,6 +3839,44 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
       return ExprError();
     break;
 
+  case Builtin::BI__builtin_stdc_bit_floor:
+  case Builtin::BI__builtin_stdc_bit_ceil:
+  case Builtin::BIstdc_bit_floor:
+  case Builtin::BIstdc_bit_ceil:
+    if (BuiltinStdCBuiltin(*this, TheCall, QualType()))
+      return ExprError();
+    break;
+  case Builtin::BI__builtin_stdc_has_single_bit:
+  case Builtin::BIstdc_has_single_bit:
+    if (BuiltinStdCBuiltin(*this, TheCall, Context.BoolTy))
+      return ExprError();
+    break;
+  case Builtin::BI__builtin_stdc_leading_zeros:
+  case Builtin::BI__builtin_stdc_leading_ones:
+  case Builtin::BI__builtin_stdc_trailing_zeros:
+  case Builtin::BI__builtin_stdc_trailing_ones:
+  case Builtin::BI__builtin_stdc_first_leading_zero:
+  case Builtin::BI__builtin_stdc_first_leading_one:
+  case Builtin::BI__builtin_stdc_first_trailing_zero:
+  case Builtin::BI__builtin_stdc_first_trailing_one:
+  case Builtin::BI__builtin_stdc_count_zeros:
+  case Builtin::BI__builtin_stdc_count_ones:
+  case Builtin::BI__builtin_stdc_bit_width:
+  case Builtin::BIstdc_leading_zeros:
+  case Builtin::BIstdc_leading_ones:
+  case Builtin::BIstdc_trailing_zeros:
+  case Builtin::BIstdc_trailing_ones:
+  case Builtin::BIstdc_first_leading_zero:
+  case Builtin::BIstdc_first_leading_one:
+  case Builtin::BIstdc_first_trailing_zero:
+  case Builtin::BIstdc_first_trailing_one:
+  case Builtin::BIstdc_count_zeros:
+  case Builtin::BIstdc_count_ones:
+  case Builtin::BIstdc_bit_width:
+    if (BuiltinStdCBuiltin(*this, TheCall, Context.UnsignedIntTy))
----------------
efriedma-quic wrote:

We probably want to error out if the result doesn't fit into an "unsigned int".  (This is probably not really a practical issue in most cases due to limits on the size of integers, but there could be some weird edge cases with _BitInt on targets where "int" is 16 bits.)

https://github.com/llvm/llvm-project/pull/185978