Check the results of tightly nested IO loops (#1123)

Such as:  write(*,*,iostat=m) ((aa(j,k),j=1,3),k=1,3)

Author: vdonaldson

flang/lib/Lower/IO.cpp

@@ -657,9 +657,14 @@ static void genIoLoop(Fortran::lower::AbstractConverter &converter,
     auto ifOp = dyn_cast<fir::IfOp>(op);
     auto *lastOp = &ifOp.thenRegion().front().back();
     builder.setInsertionPointAfter(lastOp);
-    builder.create<fir::ResultOp>(loc, lastOp->getResult(0)); // runtime result
+    // The primary ifOp result is the result of an IO call or loop.
+    if (mlir::isa<fir::CallOp, fir::IfOp>(*lastOp))
+      builder.create<fir::ResultOp>(loc, lastOp->getResult(0));
+    else
+      builder.create<fir::ResultOp>(loc, ok); // loop result
+    // The else branch propagates an early exit false result.
     builder.setInsertionPointToStart(&ifOp.elseRegion().front());
-    builder.create<fir::ResultOp>(loc, falseValue); // known false result
+    builder.create<fir::ResultOp>(loc, falseValue);
   }
   builder.setInsertionPointToEnd(iterWhileOp.getBody());
   auto iterateResult = builder.getBlock()->back().getResult(0);

flang/test/Lower/io-statement-2.f90

@@ -106,6 +106,33 @@ subroutine control2() ! I/O condition specifier control flow (use index result)
 write(*,'(8F4.1,I5)',iostat=m) (c,d,j=11,14), j
 end
 
+! CHECK-LABEL: func @_QPloopnest
+subroutine loopnest
+   integer :: aa(3,3)
+   aa = 10
+   ! CHECK: BeginExternalListOutput
+   ! CHECK: EnableHandlers
+   ! CHECK: {{.*}}:2 = fir.iterate_while ({{.*}} = {{.*}} to {{.*}} step {{.*}}) and ({{.*}} = {{.*}}) -> (index, i1) {
+   ! CHECK:   fir.if {{.*}} -> (i1) {
+   ! CHECK:     {{.*}}:2 = fir.iterate_while ({{.*}} = {{.*}} to {{.*}} step {{.*}}) and ({{.*}} = {{.*}}) -> (index, i1) {
+   ! CHECK:       fir.if {{.*}} -> (i1) {
+   ! CHECK:         OutputInteger64
+   ! CHECK:         fir.result {{.*}} : i1
+   ! CHECK:       } else {
+   ! CHECK:         fir.result {{.*}} : i1
+   ! CHECK:       }
+   ! CHECK:       fir.result {{.*}}, {{.*}} : index, i1
+   ! CHECK:     }
+   ! CHECK:     fir.result {{.*}}#1 : i1
+   ! CHECK:   } else {
+   ! CHECK:     fir.result {{.*}} : i1
+   ! CHECK:   }
+   ! CHECK:   fir.result {{.*}}, {{.*}} : index, i1
+   ! CHECK: }
+   ! CHECK: EndIoStatement
+   write(*,*,err=66) ((aa(j,k)+j+k,j=1,3),k=1,3)
+66 continue
+end
 
 ! CHECK-LABEL: func @_QPimpliedformat
 subroutine impliedformat