core.memory: Make GC.[profile]stats safe/nothrow/nogc

Those functions only return a struct, they do not accept any parameter,
and thus should be inherently safe. It also would not make sense for GC.stats
to allocate, as it would skew the metrics it returns.

Author: Geod24

src/core/gc/gcinterface.d

@@ -141,13 +141,13 @@ interface GC
      * Retrieve statistics about garbage collection.
      * Useful for debugging and tuning.
      */
-    core.memory.GC.Stats stats() nothrow;
+    core.memory.GC.Stats stats() @safe nothrow @nogc;
 
     /**
      * Retrieve profile statistics about garbage collection.
      * Useful for debugging and tuning.
      */
-    core.memory.GC.ProfileStats profileStats() nothrow @safe;
+    core.memory.GC.ProfileStats profileStats() @safe nothrow @nogc;
 
     /**
      * add p to list of roots

src/core/internal/gc/impl/conservative/gc.d

@@ -156,7 +156,7 @@ class ConservativeGC : GC
      *
      * Throws: InvalidMemoryOperationError on recursive locking during finalization.
      */
-    static void lockNR() @nogc nothrow
+    static void lockNR() @safe @nogc nothrow
     {
         if (_inFinalizer)
             onInvalidMemoryOperationError();
@@ -1300,7 +1300,7 @@ class ConservativeGC : GC
     }
 
 
-    core.memory.GC.Stats stats() nothrow
+    core.memory.GC.Stats stats() @safe nothrow @nogc
     {
         typeof(return) ret;
 
@@ -1333,8 +1333,15 @@ class ConservativeGC : GC
     //
     // Implementation of getStats
     //
-    private void getStatsNoSync(out core.memory.GC.Stats stats) nothrow
-    {
+    private void getStatsNoSync(out core.memory.GC.Stats stats) @trusted nothrow @nogc
+    {
+        // This function is trusted for two reasons: `pool.pagetable` is a pointer,
+        // which is being sliced in the below foreach, and so is `binPageChain`,
+        // also sliced a bit later in this function.
+        // However, both usages are safe as long as the assumption that `npools`
+        // defines the limit for `pagetable`'s length holds true (see allocation).
+        // The slicing happens at __LINE__ + 4 and __LINE__ + 24.
+        // `@trusted` delegates are not used to prevent any performance issue.
         foreach (pool; gcx.pooltable[])
         {
             foreach (bin; pool.pagetable[0 .. pool.npages])

src/core/internal/gc/proxy.d

@@ -209,12 +209,12 @@ extern (C)
         return instance.query( p );
     }
 
-    core.memory.GC.Stats gc_stats() nothrow
+    core.memory.GC.Stats gc_stats() @safe nothrow @nogc
     {
         return instance.stats();
     }
 
-    core.memory.GC.ProfileStats gc_profileStats() nothrow @safe
+    core.memory.GC.ProfileStats gc_profileStats() @safe nothrow @nogc
     {
         return instance.profileStats();
     }

src/core/memory.d

@@ -133,7 +133,7 @@ private
     }
 
     extern (C) BlkInfo_ gc_query(return scope void* p) pure nothrow;
-    extern (C) GC.Stats gc_stats ( ) nothrow @nogc;
+    extern (C) GC.Stats gc_stats ( ) @safe nothrow @nogc;
     extern (C) GC.ProfileStats gc_profileStats ( ) nothrow @nogc @safe;
 }
 
@@ -766,7 +766,7 @@ extern(D):
      * Returns runtime stats for currently active GC implementation
      * See `core.memory.GC.Stats` for list of available metrics.
      */
-    static Stats stats() nothrow
+    static Stats stats() @safe nothrow @nogc
     {
         return gc_stats();
     }