Initial commit of snmalloc

History squashed from internal development.

Internal history has commit hash:
  e27a0e485c44a5003a802de2661ce3b21e120316

src/test/perf/singlethread/singlethread.cc

@@ -0,0 +1,83 @@
+#include <snmalloc.h>
+#include <test/measuretime.h>
+#include <unordered_set>
+
+using namespace snmalloc;
+
+template<ZeroMem zero_mem>
+void test_alloc_dealloc(size_t count, size_t size, bool write)
+{
+  auto* alloc = ThreadAlloc::get();
+
+  DO_TIME(
+    "Count: " << std::setw(6) << count << ", Size: " << std::setw(6) << size
+              << ", ZeroMem: " << (zero_mem == YesZero) << ", Write: " << write,
+    {
+      std::unordered_set<void*> set;
+
+      // alloc 1.5x objects
+      for (size_t i = 0; i < ((count * 3) / 2); i++)
+      {
+        void* p = alloc->alloc<zero_mem>(size);
+        assert(set.find(p) == set.end());
+
+        if (write)
+          *(int*)p = 4;
+
+        set.insert(p);
+      }
+
+      // free 0.25x of the objects
+      for (size_t i = 0; i < (count / 4); i++)
+      {
+        auto it = set.begin();
+        void* p = *it;
+        alloc->dealloc(p, size);
+        set.erase(it);
+        assert(set.find(p) == set.end());
+      }
+
+      // alloc 1x objects
+      for (size_t i = 0; i < count; i++)
+      {
+        void* p = alloc->alloc<zero_mem>(size);
+        assert(set.find(p) == set.end());
+
+        if (write)
+          *(int*)p = 4;
+
+        set.insert(p);
+      }
+
+      // free everything
+      while (!set.empty())
+      {
+        auto it = set.begin();
+        alloc->dealloc(*it, size);
+        set.erase(it);
+      }
+    });
+
+  current_alloc_pool()->debug_check_empty();
+}
+
+int main(int, char**)
+{
+  for (size_t size = 16; size <= 128; size <<= 1)
+  {
+    test_alloc_dealloc<NoZero>(1 << 15, size, false);
+    test_alloc_dealloc<NoZero>(1 << 15, size, true);
+    test_alloc_dealloc<YesZero>(1 << 15, size, false);
+    test_alloc_dealloc<YesZero>(1 << 15, size, true);
+  }
+
+  for (size_t size = 1 << 12; size <= 1 << 17; size <<= 1)
+  {
+    test_alloc_dealloc<NoZero>(1 << 10, size, false);
+    test_alloc_dealloc<NoZero>(1 << 10, size, true);
+    test_alloc_dealloc<YesZero>(1 << 10, size, false);
+    test_alloc_dealloc<YesZero>(1 << 10, size, true);
+  }
+
+  return 0;
+}