PODVector Updates

Remove deprecated and unused PolymorphicAllocator. It has been replaced by
PolymorphicArenaAllocator.

Restrict PODVector's Allocator to std::allocator and AMReX's various Arena
based allocators. This simplifies the implementation of PODVector, because
std::allocator is stateless and Arena based allocators are simple even when
it's polymorphic.

Fix a few issues of PODVectors with a PolymorphicArenaAllocator. For
example, copy assignment operator should copy the Allocator. Copy
constructor should consider the possibility that other PODVector has a
different type of Arena.

Add placeholders for potentially growing and shrinking memory allocation
in-place that will be implemented in a follow-up PR.

Update PODVector's growth strategy. Hopefully this helps to reduce the
memory consumption.

  * Always try to grow in-place.

  * For assign, operator=, resize & reserve, allocate the specified size
    without capacity.

  * For push_back & emplace_back, grow the capacity by a factor that is 1.5
    by default.

  * For insert, the capacity grows either by a factor that is 1.5 by default
    or to the new size, whichever is greater.

Src/AmrCore/AMReX_TagBox.cpp

@@ -492,7 +492,7 @@ TagBoxArray::local_collate_gpu (Gpu::PinnedVector<IntVect>& v) const
  Gpu::dtoh_memcpy(hv_ntags.data(), dv_ntags.data(), ntotblocks*sizeof(int));
 
  Gpu::PinnedVector<int> hv_tags_offset(ntotblocks+1);
- hv_tags_offset[0] = 0;
+ if (! hv_tags_offset.empty()) { hv_tags_offset[0] = 0; }
  std::partial_sum(hv_ntags.begin(), hv_ntags.end(), hv_tags_offset.begin()+1);
  int ntotaltags = hv_tags_offset.back();
 

Src/Base/AMReX_Arena.H

@@ -7,6 +7,7 @@
 #include <cstddef>
 #include <cstdlib>
 #include <limits>
+#include <utility>
 
 namespace amrex {
 
@@ -100,6 +101,26 @@ public:
  * \return a pointer to the allocated memory
  */
  [[nodiscard]] virtual void* alloc (std::size_t sz) = 0;
+
+ /**
+ * Try to allocate in-place by extending the capacity of given pointer.
+ */
+ [[nodiscard]] virtual std::pair<void*,std::size_t>
+ alloc_in_place (void* /*pt*/, std::size_t /*szmin*/, std::size_t szmax)
+ {
+ auto* p = alloc(szmax);
+ return std::make_pair(p, szmax);
+ }
+
+ /**
+ * Try to shrink in-place
+ */
+ [[nodiscard]] virtual void*
+ shrink_in_place (void* /*pt*/, std::size_t sz)
+ {
+ return alloc(sz);
+ }
+
  /**
  * \brief A pure virtual function for deleting the arena pointed to by pt
  */