[flang] Return 1 in ERROR STOP without user provided stop-code (#87501)

See F'2023 section 11.4: "If the stop-code in an ERROR STOP statement is
of type character or does not appear, it is recommended that a
processor-dependent nonzero value be supplied as the process exit
status"

Fixes #66581.

flang/lib/Lower/Runtime.cpp

@@ -55,6 +55,8 @@ static void genUnreachable(fir::FirOpBuilder &builder, mlir::Location loc) {
 void Fortran::lower::genStopStatement(
     Fortran::lower::AbstractConverter &converter,
     const Fortran::parser::StopStmt &stmt) {
+  const bool isError = std::get<Fortran::parser::StopStmt::Kind>(stmt.t) ==
+                       Fortran::parser::StopStmt::Kind::ErrorStop;
   fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   mlir::Location loc = converter.getCurrentLocation();
   Fortran::lower::StatementContext stmtCtx;
@@ -94,13 +96,12 @@ void Fortran::lower::genStopStatement(
   } else {
     callee = fir::runtime::getRuntimeFunc<mkRTKey(StopStatement)>(loc, builder);
     calleeType = callee.getFunctionType();
-    operands.push_back(
-        builder.createIntegerConstant(loc, calleeType.getInput(0), 0));
+    // Default to values are advised in F'2023 11.4 p2.
+    operands.push_back(builder.createIntegerConstant(
+        loc, calleeType.getInput(0), isError ? 1 : 0));
   }
 
   // Second operand indicates ERROR STOP
-  bool isError = std::get<Fortran::parser::StopStmt::Kind>(stmt.t) ==
-                 Fortran::parser::StopStmt::Kind::ErrorStop;
   operands.push_back(builder.createIntegerConstant(
       loc, calleeType.getInput(operands.size()), isError));
 

flang/test/Lower/stop-statement.f90

@@ -21,10 +21,10 @@ subroutine stop_code()
 ! CHECK-LABEL: stop_error
 subroutine stop_error()
   error stop
- ! CHECK-DAG: %[[c0:.*]] = arith.constant 0 : i32
+ ! CHECK-DAG: %[[c_1:.*]] = arith.constant 1 : i32
  ! CHECK-DAG: %[[true:.*]] = arith.constant true
  ! CHECK-DAG: %[[false:.*]] = arith.constant false
- ! CHECK: fir.call @_Fortran{{.*}}StopStatement(%[[c0]], %[[true]], %[[false]])
+ ! CHECK: fir.call @_Fortran{{.*}}StopStatement(%[[c_1]], %[[true]], %[[false]])
  ! CHECK-NEXT: fir.unreachable
 end subroutine