[Clang][AST] Fix printing for atomic_test_and_set and atomic_clear

llvm#121943 rewrote
`__atomic_test_and_set` and `__atomic_clear` to be lowered through AtomicExpr

StmtPrinter::VisitAtomicExpr still treated them like other atomic builtins
with a Val1 operand. This led to incorrect pretty-printing when dumping
the AST.

Skip Val1 for these two builtins like atomic loads.

Author: devajithvs

clang/docs/ReleaseNotes.rst

@@ -114,6 +114,15 @@ AST Dumping Potentially Breaking Changes
 ----------------------------------------
 - How nested name specifiers are dumped and printed changes, keeping track of clang AST changes.
 
+- Pretty-printing of atomic builtins ``__atomic_test_and_set`` and ``__atomic_clear`` in ``-ast-print`` output.
+  These previously displayed an extra ``<null expr>`` argument, e.g.:
+
+    ``__atomic_test_and_set(p, <null expr>, 0)``
+
+  Now they are printed as:
+
+    ``__atomic_test_and_set(p, 0)``
+
 Clang Frontend Potentially Breaking Changes
 -------------------------------------------
 - Members of anonymous unions/structs are now injected as ``IndirectFieldDecl``

clang/include/clang/AST/Expr.h

@@ -6908,6 +6908,21 @@ class AtomicExpr : public Expr {
            getOp() == AO__scoped_atomic_compare_exchange_n;
   }
 
+  bool hasVal1Operand() const {
+    switch (getOp()) {
+    case AO__atomic_load_n:
+    case AO__scoped_atomic_load_n:
+    case AO__c11_atomic_load:
+    case AO__opencl_atomic_load:
+    case AO__hip_atomic_load:
+    case AO__atomic_test_and_set:
+    case AO__atomic_clear:
+      return false;
+    default:
+      return true;
+    }
+  }
+
   bool isOpenCL() const {
     return getOp() >= AO__opencl_atomic_compare_exchange_strong &&
            getOp() <= AO__opencl_atomic_store;

clang/lib/AST/StmtPrinter.cpp

@@ -2024,11 +2024,7 @@ void StmtPrinter::VisitAtomicExpr(AtomicExpr *Node) {
 
   // AtomicExpr stores its subexpressions in a permuted order.
   PrintExpr(Node->getPtr());
-  if (Node->getOp() != AtomicExpr::AO__c11_atomic_load &&
-      Node->getOp() != AtomicExpr::AO__atomic_load_n &&
-      Node->getOp() != AtomicExpr::AO__scoped_atomic_load_n &&
-      Node->getOp() != AtomicExpr::AO__opencl_atomic_load &&
-      Node->getOp() != AtomicExpr::AO__hip_atomic_load) {
+  if (Node->hasVal1Operand()) {
     OS << ", ";
     PrintExpr(Node->getVal1());
   }