Use backend global concept on template args

Wire the concept into the rest of the tree, being careful to avoid demanding the
result of fixed-pointing computation while tying the knot.

src/mem/corealloc.h

@@ -43,13 +43,13 @@ namespace snmalloc
    *   provided externally, then it must be set explicitly with
    *   `init_message_queue`.
    */
-  template<typename SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobalsLazy) SharedStateHandle>
   class CoreAllocator : public std::conditional_t<
                           SharedStateHandle::Options.CoreAllocIsPoolAllocated,
                           Pooled<CoreAllocator<SharedStateHandle>>,
                           NotPoolAllocated>
   {
-    template<typename SharedStateHandle2>
+    template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle2>
     friend class LocalAllocator;
 
     /**

src/mem/globalalloc.h

@@ -5,7 +5,7 @@
 
 namespace snmalloc
 {
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void aggregate_stats(Stats& stats)
   {
     static_assert(
@@ -24,7 +24,7 @@ namespace snmalloc
   }
 
 #ifdef USE_SNMALLOC_STATS
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void print_all_stats(std::ostream& o, uint64_t dumpid = 0)
   {
     static_assert(
@@ -41,7 +41,7 @@ namespace snmalloc
     }
   }
 #else
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void print_all_stats(void*& o, uint64_t dumpid = 0)
   {
     UNUSED(o);
@@ -49,7 +49,7 @@ namespace snmalloc
   }
 #endif
 
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void cleanup_unused()
   {
 #ifndef SNMALLOC_PASS_THROUGH
@@ -83,7 +83,7 @@ namespace snmalloc
     allocators are empty. If you don't pass a pointer to a bool, then will
     raise an error all the allocators are not empty.
    */
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void debug_check_empty(bool* result = nullptr)
   {
 #ifndef SNMALLOC_PASS_THROUGH
@@ -153,7 +153,7 @@ namespace snmalloc
 #endif
   }
 
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   inline static void debug_in_use(size_t count)
   {
     static_assert(

src/mem/localalloc.h

@@ -59,7 +59,7 @@ namespace snmalloc
    * core allocator must be provided externally by invoking the `init` method
    * on this class *before* any allocation-related methods are called.
    */
-  template<class SharedStateHandle>
+  template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   class LocalAllocator
   {
   public:

src/mem/pool.h

@@ -23,7 +23,7 @@ namespace snmalloc
   {
     template<
       typename TT,
-      typename SharedStateHandle,
+      SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle,
       PoolState<TT>& get_state()>
     friend class Pool;
 
@@ -42,7 +42,9 @@ namespace snmalloc
    * SingletonPoolState::pool is the default provider for the PoolState within
    * the Pool class.
    */
-  template<typename T, typename SharedStateHandle>
+  template<
+    typename T,
+    SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
   class SingletonPoolState
   {
     /**
@@ -113,7 +115,7 @@ namespace snmalloc
    */
   template<
     typename T,
-    typename SharedStateHandle,
+    SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle,
     PoolState<T>& get_state() = SingletonPoolState<T, SharedStateHandle>::pool>
   class Pool
   {

src/mem/pooled.h

@@ -13,7 +13,7 @@ namespace snmalloc
   public:
     template<
       typename TT,
-      typename SharedStateHandle,
+      SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle,
       PoolState<TT>& get_state()>
     friend class Pool;
     template<class a, Construction c>
@@ -45,4 +45,4 @@ namespace snmalloc
       return result;
     }
   };
-} // namespace snmalloc
+} // namespace snmalloc

src/mem/slaballocator.h

@@ -75,7 +75,7 @@ namespace snmalloc
   class ChunkAllocator
   {
   public:
-    template<typename SharedStateHandle>
+    template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
     static std::pair<CapPtr<void, CBChunk>, Metaslab*> alloc_chunk(
       typename SharedStateHandle::LocalState& local_state,
       sizeclass_t sizeclass,
@@ -130,7 +130,7 @@ namespace snmalloc
       return {slab, meta};
     }
 
-    template<typename SharedStateHandle>
+    template<SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle>
     SNMALLOC_SLOW_PATH static void dealloc(
       typename SharedStateHandle::LocalState& local_state,
       ChunkRecord* p,
@@ -153,7 +153,10 @@ namespace snmalloc
      * Backend allocator may use guard pages and separate area of
      * address space to protect this from corruption.
      */
-    template<typename U, typename SharedStateHandle, typename... Args>
+    template<
+      typename U,
+      SNMALLOC_CONCEPT(ConceptBackendGlobals) SharedStateHandle,
+      typename... Args>
     static U* alloc_meta_data(
       typename SharedStateHandle::LocalState* local_state, Args&&... args)
     {