[flang] Don't generate empty else blocks (llvm#106618)

Code lowering always generates fir.if else blocks for source level if
statements, whether needed or not. Change this to only generate else
blocks that are needed.

Author: vdonaldson

flang/lib/Lower/Bridge.cpp

@@ -2349,8 +2349,11 @@ class FirConverter : public Fortran::lower::AbstractConverter {
       fir::IfOp topIfOp, currentIfOp;
       for (Fortran::lower::pft::Evaluation &e : eval.getNestedEvaluations()) {
         auto genIfOp = [&](mlir::Value cond) {
-          auto ifOp =
-              builder->create<fir::IfOp>(toLocation(), cond, /*withElse=*/true);
+          Fortran::lower::pft::Evaluation &succ = *e.controlSuccessor;
+          bool hasElse = succ.isA<Fortran::parser::ElseIfStmt>() ||
+                         succ.isA<Fortran::parser::ElseStmt>();
+          auto ifOp = builder->create<fir::IfOp>(toLocation(), cond,
+                                                 /*withElseRegion=*/hasElse);
           builder->setInsertionPointToStart(&ifOp.getThenRegion().front());
           return ifOp;
         };

flang/test/HLFIR/assumed_shape_with_value_keyword.f90

@@ -102,7 +102,6 @@ subroutine test_optional1(x)
 ! CHECK:            %[[VAL_3:.*]] = fir.box_addr %[[VAL_2]]#0 : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<!fir.array<?xf32>>
 ! CHECK:            fir.call @_QPinternal_call7(%[[VAL_3]]) fastmath<contract> : (!fir.ref<!fir.array<?xf32>>) -> ()
 ! CHECK:            hlfir.copy_out %[[TMP_BOX]], %[[VAL_2]]#1 to %[[VAL_0]]#0 : (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf32>>>>, i1, !fir.box<!fir.array<?xf32>>) -> ()
-! CHECK:          } else {
 ! CHECK:          }
 ! CHECK:          return
 ! CHECK:        }
@@ -122,7 +121,6 @@ subroutine test_optional2(x)
 ! CHECK:            %[[VAL_3:.*]] = fir.box_addr %[[VAL_2]]#0 : (!fir.box<!fir.array<?x?xf32>>) -> !fir.ref<!fir.array<?x?xf32>>
 ! CHECK:            fir.call @_QPinternal_call8(%[[VAL_3]]) fastmath<contract> : (!fir.ref<!fir.array<?x?xf32>>) -> ()
 ! CHECK:            hlfir.copy_out %[[TMP_BOX]], %[[VAL_2]]#1 to %[[VAL_0]]#0 : (!fir.ref<!fir.box<!fir.heap<!fir.array<?x?xf32>>>>, i1, !fir.box<!fir.array<?x?xf32>>) -> ()
-! CHECK:          } else {
 ! CHECK:          }
 ! CHECK:          return
 ! CHECK:        }

flang/test/Lower/HLFIR/select-rank.f90

@@ -796,7 +796,6 @@ subroutine test_branching(x)
 ! CHECK:           %[[VAL_10:.*]] = arith.xori %[[VAL_8]], %[[VAL_9]] : i1
 ! CHECK:           fir.if %[[VAL_10]] {
 ! CHECK:             fir.call @_QPone() fastmath<contract> : () -> ()
-! CHECK:           } else {
 ! CHECK:           }
 ! CHECK:           fir.call @_QPrdefault(%[[VAL_6]]#0) fastmath<contract> : (!fir.box<!fir.array<*:f32>>) -> ()
 ! CHECK:           cf.br ^bb7

flang/test/Lower/Intrinsics/system_clock.f90

@@ -104,7 +104,6 @@ subroutine ss(count)
   ! CHECK:   fir.if %[[V_17]] {
   ! CHECK:     %[[C_0:c[0-9a-z_]+]] = arith.constant 0 : i64
   ! CHECK:     fir.store %[[C_0]] to %arg0 : !fir.ref<i64>
-  ! CHECK:   } else {
   ! CHECK:   }
   ! CHECK:   %[[V_18:[0-9]+]] = fir.zero_bits !fir.ptr<i64>
   ! CHECK:   fir.store %[[V_18]] to %[[V_4]] : !fir.ref<!fir.ptr<i64>>
@@ -137,7 +136,6 @@ subroutine ss(count)
   ! CHECK:     %[[V_32]] = fir.load %arg0 : !fir.ref<i64>
   ! CHECK:     %[[V_33]] = fir.call @_FortranAioOutputInteger64(%[[V_31]], %[[V_32]]) {{.*}}: (!fir.ref<i8>, i64) -> i1
   ! CHECK:     %[[V_34]] = fir.call @_FortranAioEndIoStatement(%[[V_31]]) {{.*}}: (!fir.ref<i8>) -> i32
-  ! CHECK:   } else {
   ! CHECK:   }
   ! CHECK:   return
   ! CHECK: }

flang/test/Lower/OpenMP/master.f90

@@ -91,7 +91,7 @@ subroutine omp_master_parallel()
         !CHECK: hlfir.assign %{{.*}} to %{{.*}}#0 : i32, !fir.ref<i32>
         beta = alpha + gama
     end if
-    !CHECK: else
+    !CHECK: }
 
 !CHECK: omp.terminator
 !$omp end master

flang/test/Lower/OpenMP/unstructured.f90

@@ -141,7 +141,6 @@ subroutine ss3(n) ! nested unstructured OpenMP constructs
 ! CHECK:              @_FortranAioBeginExternalListOutput
 ! CHECK:              %[[LOAD:.*]] = fir.load %[[OMP_LOOP_J_DECL]]#0 : !fir.ref<i32>
 ! CHECK:              @_FortranAioOutputInteger32(%{{.*}}, %[[LOAD]])
-! CHECK:             } else {
 ! CHECK:             }
 ! CHECK-NEXT:        omp.yield
 ! CHECK-NEXT:      }

flang/test/Lower/OpenMP/wsloop-reduction-max-byref.f90

@@ -118,7 +118,6 @@
 ! CHECK:                   %[[VAL_46:.*]] = hlfir.designate %[[VAL_5]]#0 (%[[VAL_45]])  : (!fir.box<!fir.array<?xf32>>, i64) -> !fir.ref<f32>
 ! CHECK:                   %[[VAL_47:.*]] = fir.load %[[VAL_46]] : !fir.ref<f32>
 ! CHECK:                   hlfir.assign %[[VAL_47]] to %[[VAL_37]]#0 : f32, !fir.ref<f32>
-! CHECK:                 } else {
 ! CHECK:                 }
 ! CHECK:                 omp.yield
 ! CHECK:               omp.terminator

flang/test/Lower/OpenMP/wsloop-reduction-max.f90

@@ -108,7 +108,6 @@
 ! CHECK:                   %[[VAL_46:.*]] = hlfir.designate %[[VAL_5]]#0 (%[[VAL_45]])  : (!fir.box<!fir.array<?xf32>>, i64) -> !fir.ref<f32>
 ! CHECK:                   %[[VAL_47:.*]] = fir.load %[[VAL_46]] : !fir.ref<f32>
 ! CHECK:                   hlfir.assign %[[VAL_47]] to %[[VAL_37]]#0 : f32, !fir.ref<f32>
-! CHECK:                 } else {
 ! CHECK:                 }
 ! CHECK:                 omp.yield
 ! CHECK:               omp.terminator

flang/test/Lower/OpenMP/wsloop-reduction-min-byref.f90

@@ -120,7 +120,6 @@
 ! CHECK:                   %[[VAL_46:.*]] = hlfir.designate %[[VAL_5]]#0 (%[[VAL_45]])  : (!fir.box<!fir.array<?xf32>>, i64) -> !fir.ref<f32>
 ! CHECK:                   %[[VAL_47:.*]] = fir.load %[[VAL_46]] : !fir.ref<f32>
 ! CHECK:                   hlfir.assign %[[VAL_47]] to %[[VAL_37]]#0 : f32, !fir.ref<f32>
-! CHECK:                 } else {
 ! CHECK:                 }
 ! CHECK:                 omp.yield
 ! CHECK:               omp.terminator

flang/test/Lower/OpenMP/wsloop-reduction-min.f90

@@ -110,7 +110,6 @@
 ! CHECK:                   %[[VAL_46:.*]] = hlfir.designate %[[VAL_5]]#0 (%[[VAL_45]])  : (!fir.box<!fir.array<?xf32>>, i64) -> !fir.ref<f32>
 ! CHECK:                   %[[VAL_47:.*]] = fir.load %[[VAL_46]] : !fir.ref<f32>
 ! CHECK:                   hlfir.assign %[[VAL_47]] to %[[VAL_37]]#0 : f32, !fir.ref<f32>
-! CHECK:                 } else {
 ! CHECK:                 }
 ! CHECK:                 omp.yield
 ! CHECK:               omp.terminator

flang/test/Lower/OpenMP/wsloop-variable.f90

@@ -190,7 +190,6 @@ subroutine wsloop_variable_sub
 !CHECK:               %[[VAL_56:.*]] = fir.load %[[VAL_19]]#0 : !fir.ref<i8>
 !CHECK:               %[[VAL_57:.*]] = arith.cmpi eq, %[[VAL_55]], %[[VAL_56]] : i8
 !CHECK:               fir.if %[[VAL_57]] {
-!CHECK:               } else {
 !CHECK:               }
 !CHECK:               omp.yield
 !CHECK:             }