cleaning and fixes for PureSoA ParticleTile (#3327)

## Summary

* fix return by value/reference mismatch of `id()` and `cpu()` with
`decltype(auto)`
* update `packParticleData` and `unpackParticleData` for PureSoA
* change `getSuperParticle` and add `setSuperParticle` for PureSoA.
Remaining issue: super particle has redundant/unused fields for
positions, id and cpu
* update `ConstParticleTileData` for PureSoA
* don’t call `getParticleTileData` in `ParticleTile::id()` etc. as this
could be very slow if used in a for loop
* use if constexpr instead if SFINAE in a number of places
* change PODVector constructor so that `getParticleTileData()` won't
allocate memory if no runtime components are used

## Additional background

Follow-up to #2878.

## Checklist

The proposed changes:
- [x] fix a bug or incorrect behavior in AMReX
- [ ] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [ ] include documentation in the code and/or rst files, if appropriate

Src/Base/AMReX_PODVector.H

@@ -262,32 +262,40 @@ namespace amrex
         explicit PODVector (size_type a_size) noexcept
             : m_data(nullptr), m_size(a_size)
         {
-            AllocateBuffer(GetNewCapacity(a_size));
+            if (a_size != 0) {
+                AllocateBuffer(GetNewCapacity(a_size));
+            }
         }
 
         PODVector (size_type a_size, const value_type& a_value,
                    const allocator_type& a_allocator = Allocator()) noexcept
             : Allocator(a_allocator), m_data(nullptr), m_size(a_size)
         {
-            AllocateBuffer(GetNewCapacity(a_size));
-            detail::uninitializedFillNImpl<Allocator>(m_data, a_size, a_value, *this);
+            if (a_size != 0) {
+                AllocateBuffer(GetNewCapacity(a_size));
+                detail::uninitializedFillNImpl<Allocator>(m_data, a_size, a_value, *this);
+            }
         }
 
         PODVector (std::initializer_list<T> a_initializer_list,
                    const allocator_type& a_allocator = Allocator()) noexcept
             : Allocator(a_allocator), m_data(nullptr), m_size(a_initializer_list.size())
         {
-            AllocateBuffer(GetNewCapacity(m_size));
-            detail::initFromListImpl<Allocator>(m_data, a_initializer_list, *this);
+            if (a_initializer_list.size() != 0) {
+                AllocateBuffer(GetNewCapacity(m_size));
+                detail::initFromListImpl<Allocator>(m_data, a_initializer_list, *this);
+            }
         }
 
         PODVector (const PODVector<T, Allocator>& a_vector) noexcept
             : Allocator(a_vector), m_data(nullptr), m_size(a_vector.size())
         {
             using namespace detail;
-            AllocateBuffer(a_vector.capacity());
-            auto r = memCopyImpl<Allocator>(m_data, a_vector.m_data, a_vector.size() * sizeof(T), *this);
-            if (r) { Gpu::streamSynchronize(); }
+            if (a_vector.size() != 0) {
+                AllocateBuffer(a_vector.capacity());
+                auto r = memCopyImpl<Allocator>(m_data, a_vector.m_data, a_vector.size() * sizeof(T), *this);
+                if (r) { Gpu::streamSynchronize(); }
+            }
         }
 
         PODVector (PODVector<T, Allocator>&& a_vector) noexcept

Src/F_Interfaces/Particle/AMReX_particlecontainer_fi.cpp

@@ -69,7 +69,8 @@ extern "C" {
     }
 
     void amrex_fi_get_particles_mfi(FParticleContainer* particlecontainer,
-                                    int lev, MFIter* mfi, ParticleReal*& dp, Long& np)
+                                    int lev, MFIter* mfi,
+                                    FParticleContainer::ParticleType*& dp, Long& np)
     {
         const int grid = mfi->index();
         const int tile = mfi->LocalTileIndex();
@@ -116,7 +117,8 @@ extern "C" {
     }
 
     void amrex_fi_get_particles_i(FParticleContainer* particlecontainer,
-                                  int lev, int grid, int tile, ParticleReal*& dp, Long& np)
+                                  int lev, int grid, int tile,
+                                  FParticleContainer::ParticleType*& dp, Long& np)
     {
         auto& particle_level = particlecontainer->GetParticles(lev);
         auto search = particle_level.find(std::make_pair(grid, tile));

Src/Particle/AMReX_ArrayOfStructs.H

@@ -62,15 +62,15 @@ public:
         resize(nrp + num_neighbors);
     }
 
-    [[nodiscard]] int getNumNeighbors () { return m_num_neighbor_particles; }
+    [[nodiscard]] int getNumNeighbors () const { return m_num_neighbor_particles; }
 
     [[nodiscard]] bool empty () const { return m_data.empty(); }
 
-    [[nodiscard]] const RealType* data () const { return &(m_data[0].m_pos[0]); }
-    [[nodiscard]]       RealType* data ()       { return &(m_data[0].m_pos[0]); }
+    [[nodiscard]] const ParticleType* data () const { return m_data.data(); }
+    [[nodiscard]]       ParticleType* data ()       { return m_data.data(); }
 
-    [[nodiscard]] const RealType* dataPtr () const { return data(); }
-    [[nodiscard]]       RealType* dataPtr ()       { return data(); }
+    [[nodiscard]] const ParticleType* dataPtr () const { return data(); }
+    [[nodiscard]]       ParticleType* dataPtr ()       { return data(); }
 
     [[nodiscard]] std::pair<int,int> dataShape () const {
         return std::make_pair(SizeInReal, static_cast<int>(m_data.size()));

Src/Particle/AMReX_ParticleContainerI.H

@@ -1090,9 +1090,8 @@ ParticleContainer_impl<ParticleType, NArrayReal, NArrayInt, Allocator>
 ::ReorderParticles (int lev, const MFIter& mfi, const index_type* permutations)
 {
     auto& ptile           = ParticlesAt(lev, mfi);
-    auto& aos             = ptile.GetArrayOfStructs();
-    const size_t np       = aos.numParticles();
-    const size_t np_total = np + aos.numNeighborParticles();
+    const size_t np       = ptile.numParticles();
+    const size_t np_total = np + ptile.numNeighborParticles();
 
     if (memEfficientSort) {
         if constexpr(!ParticleType::is_soa_particle) {