[flang][cuda] Allow if stmt in device subroutine (#89347)

flang/lib/Semantics/check-cuda.cpp

@@ -344,6 +344,9 @@ template <bool IsCUFKernelDo> class DeviceContextChecker {
             [&](const common::Indirection<parser::BackspaceStmt> &x) {
               WarnOnIoStmt(source);
             },
+            [&](const common::Indirection<parser::IfStmt> &x) {
+              Check(x.value());
+            },
             [&](const auto &x) {
               if (auto msg{ActionStmtChecker<IsCUFKernelDo>::WhyNotOk(x)}) {
                 context_.Say(source, std::move(*msg));
@@ -369,6 +372,13 @@ template <bool IsCUFKernelDo> class DeviceContextChecker {
       Check(std::get<parser::Block>(eb->t));
     }
   }
+  void Check(const parser::IfStmt &is) {
+    const auto &uS{
+        std::get<parser::UnlabeledStatement<parser::ActionStmt>>(is.t)};
+    CheckUnwrappedExpr(
+        context_, uS.source, std::get<parser::ScalarLogicalExpr>(is.t));
+    Check(uS.statement, uS.source);
+  }
   void Check(const parser::LoopControl::Bounds &bounds) {
     Check(bounds.lower);
     Check(bounds.upper);

flang/test/Semantics/cuf11.cuf

@@ -30,3 +30,7 @@ logical function compare_h(a,b)
 !ERROR: 'b' is not an object of derived type; it is implicitly typed
   compare_h = (a%h .eq. b%h)
 end
+
+attributes(global) subroutine sub2()
+  if (threadIdx%x == 1) print *, "I'm number one"
+end subroutine