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Draft: Fix Realm Pointer UB

Jacob Faibussowitsch requested to merge jacobf/2023-09-19/fix-realm-point-ub into master

Struct members are guaranteed to be ordered as written, but there is no guarantee in any way shape or form of their alignment or layout, so

struct Foo
{
  int x, y;
  
  int get_y() { return &x + 1; }
};

is about as "safe" as

int foo() 
{
  int x;
  char z;
  int y;

  assert(&y == (char *)&x + sizeof(int) + 1); // not guaranteed to be true!
}

Rectify this in Legion::Realm::Point, as highlighted by GCC's -Wstringop-overflow

_deps/legion-src/runtime/legion/region_tree.inl:5614:20: warning: writing 16 bytes into a region of size 4 [-Wstringop-overflow=]
#9 856.9  5614 |           point[i] = coords[i];
#9 856.9       |           ~~~~~~~~~^~~~~~~~~

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