Refactor: Remove unused features and functions, and move most allocator operations to a global namespace. (#750)

* Factor out explicit Config type

Instead of using snmalloc::Alloc::Config, expose snmalloc::Config, which is then used to derive the allocator type.

* Move globalalloc to front end.

* Remove unneed template parameter from global snmalloc functions.

* Remove SNMALLOC_PASS_THROUGH

VeronaRT now has an abstraction layer which can easily replace the allocator.
Having such a complex integration still in snmalloc does not make sense.

* Take some global functions off of local alloc.

* Drop comparison overloads on atomic Capptr.

Performing a comparison on two atomic ptr is a complex operation, and should not be implicit.  The memory model order and such things needs to be considered by the caller.

* Remove function_ref and use templates

The implementation prefers to use templates over the function_ref.  This now only exists in the Pal for a currently unused feature.

* Removing function_ref reduces stl needs.

* Remove use of __is_convertible to support older g++

* Inline function that is only used once.

* Remove unused function

* Restrict ThreadAlloc usage to globalalloc

This commit introduces various inline functions on snmalloc:: that perform allocation/deallocation using the thread local allocator.

They remove all usage from a particular test.

* Move cheri checks to own file.

* Refactor is_owned checks.

* Move alloc_size and check_size to globalalloc.

* Minor simplification of dealloc path

* Fix up is_owned to take a config

* Improve usage of scoped allocator.

* Handle Config_ in globalalloc.

src/test/perf/memcpy/memcpy.cc

@@ -35,7 +35,7 @@ void shape(size_t size)
     // the memcpys. constexpr size_t alignment = 16; offset = (my_random() %
     // size / alignment) * alignment;
     Shape s;
-    s.object = ThreadAlloc::get().alloc(rsize);
+    s.object = snmalloc::alloc(rsize);
     s.dst = static_cast<unsigned char*>(s.object) + offset;
     // Bring into cache the destination of the copy.
     memset(s.dst, 0xFF, size);
@@ -47,7 +47,7 @@ void unshape()
 {
   for (auto& s : allocs)
   {
-    ThreadAlloc::get().dealloc(s.object);
+    snmalloc::dealloc(s.object);
   }
   allocs.clear();
 }
@@ -68,7 +68,7 @@ void test(
   Memcpy mc,
   std::vector<std::pair<size_t, std::chrono::nanoseconds>>& stats)
 {
-  auto src = ThreadAlloc::get().alloc(size);
+  auto src = snmalloc::alloc(size);
   shape(size);
   for (size_t i = 0; i < 10; i++)
   {
@@ -77,7 +77,7 @@ void test(
     auto time = m.get_time();
     stats.push_back({size, time});
   }
-  ThreadAlloc::get().dealloc(src);
+  snmalloc::dealloc(src);
   unshape();
 }
 
@@ -108,7 +108,6 @@ void memcpy_platform_checked(void* dst, const void* src, size_t size)
 int main(int argc, char** argv)
 {
   opt::Opt opt(argc, argv);
-#ifndef SNMALLOC_PASS_THROUGH
   bool full_test = opt.has("--full_test");
 
   //  size_t size = 0;
@@ -182,8 +181,5 @@ int main(int argc, char** argv)
     stats_platform.clear();
     stats_platform_checked.clear();
   }
-#else
-  snmalloc::UNUSED(opt);
-#endif
   return 0;
 }