[flang][OpenMP] Fix firstprivate in DO SIMD with lastprivate

Use wsloopItemDSP instead of simdItemDSP in genCompositeDoSimd to
ensure firstprivate clauses are properly handled for the composite
DO SIMD construct.

Fixes #168306

Author: Krish Gupta

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -3324,7 +3324,7 @@ static mlir::omp::WsloopOp genCompositeDoSimd(
   genLoopNestOp(converter, symTable, semaCtx, eval, loc, queue, simdItem,
                 loopNestClauseOps, iv,
                 {{wsloopOp, wsloopArgs}, {simdOp, simdArgs}},
-                llvm::omp::Directive::OMPD_do_simd, simdItemDSP);
+                llvm::omp::Directive::OMPD_do_simd, wsloopItemDSP);
   return wsloopOp;
 }
 

flang/test/Integration/OpenMP/do-simd-firstprivate-lastprivate-runtime.f90

@@ -0,0 +1,46 @@
+! Test runtime behavior of DO SIMD with firstprivate and lastprivate on same variable
+! This is the reproducer from issue #168306
+
+! RUN: %flang_fc1 -fopenmp -emit-llvm %s -o - | FileCheck %s --check-prefix=LLVM
+! RUN: %flang -fopenmp %s -o %t && %t | FileCheck %s
+
+! LLVM-LABEL: define {{.*}} @_QQmain
+program main
+  integer :: a
+  integer :: i
+  
+  a = 10
+  !$omp do simd lastprivate(a) firstprivate(a)
+  do i = 1, 1
+     ! Inside loop: a should be 10 (from firstprivate initialization)
+     ! CHECK: main1 : a = 10
+     print *, "main1 : a = ", a
+     a = 20
+  end do
+  !$omp end do simd
+  ! After loop: a should be 20 (from lastprivate copy-out)
+  ! CHECK: main2 : a = 20
+  print *, "main2 : a = ", a
+  
+  call sub
+  ! CHECK: pass
+  print *, 'pass'
+end program main
+
+subroutine sub
+  integer :: a
+  integer :: i
+  
+  a = 10
+  !$omp do simd lastprivate(a) firstprivate(a)
+  do i = 1, 1
+     ! Inside loop: a should be 10 (from firstprivate initialization)
+     ! CHECK: sub1  : a = 10
+     print *, "sub1  : a = ", a
+     a = 20
+  end do
+  !$omp end do simd
+  ! After loop: a should be 20 (from lastprivate copy-out)
+  ! CHECK: sub2  : a = 20
+  print *, "sub2  : a = ", a
+end subroutine sub

flang/test/Lower/OpenMP/do-simd-firstprivate-lastprivate.f90

@@ -0,0 +1,87 @@
+! Test for DO SIMD with the same variable in both firstprivate and lastprivate clauses
+! This tests the fix for issue #168306
+
+! RUN: %flang_fc1 -fopenmp -mmlir --openmp-enable-delayed-privatization-staging=true -emit-hlfir %s -o - | FileCheck %s
+
+! Test case 1: Basic test with firstprivate + lastprivate on same variable
+! CHECK-LABEL: func.func @_QPdo_simd_first_last_same_var
+subroutine do_simd_first_last_same_var()
+  integer :: a
+  integer :: i
+  a = 10
+
+  ! CHECK:      omp.wsloop
+  ! CHECK-SAME: private(@{{.*}}firstprivate{{.*}} %{{.*}} -> %[[FIRSTPRIV_A:.*]] : !fir.ref<i32>)
+  ! CHECK-NEXT: omp.simd
+  ! CHECK-SAME: private(@{{.*}} %{{.*}} -> %[[PRIV_A:.*]], @{{.*}} %{{.*}} -> %[[PRIV_I:.*]] : !fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK-NEXT: omp.loop_nest (%[[IV:.*]]) : i32
+  !$omp do simd firstprivate(a) lastprivate(a)
+  do i = 1, 1
+    ! CHECK: %[[FIRSTPRIV_A_DECL:.*]]:2 = hlfir.declare %[[FIRSTPRIV_A]]
+    ! CHECK: %[[PRIV_A_DECL:.*]]:2 = hlfir.declare %[[PRIV_A]]
+    ! CHECK: %[[PRIV_I_DECL:.*]]:2 = hlfir.declare %[[PRIV_I]]
+    ! The private copy should be initialized from firstprivate (value 10)
+    ! and then modified to 20
+    a = 20
+  end do
+  !$omp end do simd
+  ! After the loop, 'a' should be 20 due to lastprivate
+end subroutine do_simd_first_last_same_var
+
+! Test case 2: Test with lastprivate and firstprivate in reverse order
+! CHECK-LABEL: func.func @_QPdo_simd_last_first_reverse
+subroutine do_simd_last_first_reverse()
+  integer :: a
+  integer :: i
+  a = 10
+
+  ! CHECK:      omp.wsloop
+  ! CHECK-SAME: private(@{{.*}}firstprivate{{.*}} %{{.*}} -> %[[FIRSTPRIV_A:.*]] : !fir.ref<i32>)
+  ! CHECK-NEXT: omp.simd
+  !$omp do simd lastprivate(a) firstprivate(a)
+  do i = 1, 1
+    a = 20
+  end do
+  !$omp end do simd
+end subroutine do_simd_last_first_reverse
+
+! Test case 3: Multiple variables with mixed privatization
+! CHECK-LABEL: func.func @_QPdo_simd_multiple_vars
+subroutine do_simd_multiple_vars()
+  integer :: a, b, c
+  integer :: i
+  a = 10
+  b = 20
+  c = 30
+
+  ! CHECK:      omp.wsloop
+  ! CHECK-SAME: private(@{{.*}}firstprivate{{.*}} %{{.*}} -> %{{.*}}, @{{.*}}firstprivate{{.*}} %{{.*}} -> %{{.*}} : !fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK-NEXT: omp.simd
+  !$omp do simd firstprivate(a, b) lastprivate(a) private(c)
+  do i = 1, 5
+    a = a + 1
+    b = b + 1
+    c = i
+  end do
+  !$omp end do simd
+end subroutine do_simd_multiple_vars
+
+! Test case 4: Reproducer from issue #168306
+! CHECK-LABEL: func.func @_QPissue_168306_reproducer
+subroutine issue_168306_reproducer()
+  integer :: a
+  integer :: i
+  a = 10
+
+  ! CHECK:      omp.wsloop
+  ! CHECK-SAME: private(@{{.*}}firstprivate{{.*}} %{{.*}} -> %[[FIRSTPRIV_A:.*]] : !fir.ref<i32>)
+  ! CHECK-NEXT: omp.simd
+  !$omp do simd lastprivate(a) firstprivate(a)
+  do i = 1, 1
+    ! Inside the loop, 'a' should start at 10 (from firstprivate)
+    ! This is the key behavior that was broken
+    a = 20
+  end do
+  !$omp end do simd
+  ! After the loop, 'a' should be 20 (from lastprivate)
+end subroutine issue_168306_reproducer