Disable use of _ExtInt with '__atomic' builtins

We're (temporarily) disabling ExtInt for the '__atomic' builtins so we can better design their behavior later. The idea is until we do an audit/design for the way atomic builtins are supposed to work with _ExtInt, we should leave them restricted so they don't limit our future options, such as by binding us to a sub-optimal implementation via ABI.

Example after this change:

    $ cat test.c

        void f(_ExtInt(64) *ptr) {
          __atomic_fetch_add(ptr, 1, 0);
        }

    $ clang -c test.c

        test.c:2:22: error: argument to atomic builtin of type '_ExtInt' is not supported
          __atomic_fetch_add(ptr, 1, 0);
                             ^
        1 error generated.

Differential Revision: https://reviews.llvm.org/D84049

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6038,9 +6038,8 @@ def err_func_def_incomplete_result : Error<
 def err_atomic_specifier_bad_type
     : Error<"_Atomic cannot be applied to "
             "%select{incomplete |array |function |reference |atomic |qualified "
-            "|sizeless ||integer |integer }0type "
-            "%1 %select{|||||||which is not trivially copyable|with less than "
-            "1 byte of precision|with a non power of 2 precision}0">;
+            "|sizeless ||integer }0type "
+            "%1 %select{|||||||which is not trivially copyable|}0">;
 
 // Expressions.
 def ext_sizeof_alignof_function_type : Extension<
@@ -7967,6 +7966,8 @@ def err_atomic_exclusive_builtin_pointer_size : Error<
   " 1,2,4 or 8 byte type (%0 invalid)">;
 def err_atomic_builtin_ext_int_size : Error<
   "Atomic memory operand must have a power-of-two size">;
+def err_atomic_builtin_ext_int_prohibit : Error<
+  "argument to atomic builtin of type '_ExtInt' is not supported">;
 def err_atomic_op_needs_atomic : Error<
   "address argument to atomic operation must be a pointer to _Atomic "
   "type (%0 invalid)">;

clang/lib/Sema/SemaChecking.cpp

@@ -5050,6 +5050,11 @@ ExprResult Sema::BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
                 ? 0
                 : 1);
 
+  if (ValType->isExtIntType()) {
+    Diag(Ptr->getExprLoc(), diag::err_atomic_builtin_ext_int_prohibit);
+    return ExprError();
+  }
+
   return AE;
 }
 

clang/lib/Sema/SemaType.cpp

@@ -8963,11 +8963,8 @@ QualType Sema::BuildAtomicType(QualType T, SourceLocation Loc) {
     else if (!T.isTriviallyCopyableType(Context))
       // Some other non-trivially-copyable type (probably a C++ class)
       DisallowedKind = 7;
-    else if (auto *ExtTy = T->getAs<ExtIntType>()) {
-      if (ExtTy->getNumBits() < 8)
+    else if (T->isExtIntType()) {
         DisallowedKind = 8;
-      else if (!llvm::isPowerOf2_32(ExtTy->getNumBits()))
-        DisallowedKind = 9;
     }
 
     if (DisallowedKind != -1) {

clang/test/Sema/builtins.c

@@ -285,12 +285,16 @@ void test_ei_i42i(_ExtInt(42) *ptr, int value) {
   __sync_fetch_and_add(ptr, value); // expected-error {{Atomic memory operand must have a power-of-two size}}
   // expected-warning@+1 {{the semantics of this intrinsic changed with GCC version 4.4 - the newer semantics are provided here}}
   __sync_nand_and_fetch(ptr, value); // expected-error {{Atomic memory operand must have a power-of-two size}}
+
+  __atomic_fetch_add(ptr, 1, 0); // expected-error {{argument to atomic builtin of type '_ExtInt' is not supported}}
 }
 
 void test_ei_i64i(_ExtInt(64) *ptr, int value) {
   __sync_fetch_and_add(ptr, value); // expect success
   // expected-warning@+1 {{the semantics of this intrinsic changed with GCC version 4.4 - the newer semantics are provided here}}
   __sync_nand_and_fetch(ptr, value); // expect success
+
+  __atomic_fetch_add(ptr, 1, 0); // expected-error {{argument to atomic builtin of type '_ExtInt' is not supported}}
 }
 
 void test_ei_ii42(int *ptr, _ExtInt(42) value) {

clang/test/SemaCXX/ext-int.cpp

@@ -91,10 +91,11 @@ typedef _ExtInt(32) __attribute__((vector_size(16))) VecTy;
 _Complex _ExtInt(3) Cmplx;
 
 // Reject cases of _Atomic:
-// expected-error@+1{{_Atomic cannot be applied to integer type '_ExtInt(4)' with less than 1 byte of precision}}
+// expected-error@+1{{_Atomic cannot be applied to integer type '_ExtInt(4)'}}
 _Atomic _ExtInt(4) TooSmallAtomic;
-// expected-error@+1{{_Atomic cannot be applied to integer type '_ExtInt(9)' with a non power of 2 precision}}
+// expected-error@+1{{_Atomic cannot be applied to integer type '_ExtInt(9)'}}
 _Atomic _ExtInt(9) NotPow2Atomic;
+// expected-error@+1{{_Atomic cannot be applied to integer type '_ExtInt(128)'}}
 _Atomic _ExtInt(128) JustRightAtomic;
 
 // Test result types of Unary/Bitwise/Binary Operations:

libcxx/test/libcxx/atomics/ext-int.verify.cpp

@@ -0,0 +1,11 @@
+// REQUIRES: clang-11
+
+#include <atomic>
+
+int main(int, char**)
+{
+  // expected-error@atomic:*1 {{_Atomic cannot be applied to integer type '_ExtInt(32)'}}
+  std::atomic<_ExtInt(32)> x {42};
+
+  return 0;
+}