[release/9.0-staging] [mono] Switch generic instance cache back to GHashTable; improve ginst hash function (#113316)

Backport of #113287

This change will revert to the hashtable container used for the generic instance cache in .NET 8.0 to address a performance regression introduced by changing to a different container in 9. Also improves the hash function used for the cache (the existing one was suboptimal.)

Co-authored-by: Katelyn Gadd <[email protected]>

Author: github-actions[bot]

src/mono/mono/metadata/loader-internals.h

@@ -175,7 +175,8 @@ struct _MonoMemoryManager {
 	MonoAssemblyLoadContext **alcs;
 
 	// Generic-specific caches
-	dn_simdhash_ght_t *ginst_cache, *gmethod_cache, *gsignature_cache;
+	GHashTable *ginst_cache;
+	dn_simdhash_ght_t *gmethod_cache, *gsignature_cache;
 	MonoConcurrentHashTable *gclass_cache;
 
 	/* mirror caches of ones already on MonoImage. These ones contain generics */

src/mono/mono/metadata/memory-manager.c

@@ -238,7 +238,7 @@ memory_manager_delete (MonoMemoryManager *memory_manager, gboolean debug_unload)
 	MonoMemoryManager *mm = memory_manager;
 	if (mm->gclass_cache)
 		mono_conc_hashtable_destroy (mm->gclass_cache);
-	free_simdhash (&mm->ginst_cache);
+	free_hash (&mm->ginst_cache);
 	free_simdhash (&mm->gmethod_cache);
 	free_simdhash (&mm->gsignature_cache);
 	free_hash (&mm->szarray_cache);

src/mono/mono/metadata/metadata.c

@@ -38,6 +38,7 @@
 #include <mono/utils/atomic.h>
 #include <mono/utils/unlocked.h>
 #include <mono/utils/mono-logger-internals.h>
+#include "../native/containers/dn-simdhash-utils.h"
 
 /* Auxiliary structure used for caching inflated signatures */
 typedef struct {
@@ -1874,18 +1875,21 @@ mono_type_equal (gconstpointer ka, gconstpointer kb)
 guint
 mono_metadata_generic_inst_hash (gconstpointer data)
 {
+	// Custom MurmurHash3 for generic instances to produce a high quality hash
 	const MonoGenericInst *ginst = (const MonoGenericInst *) data;
-	guint hash = 0;
 	g_assert (ginst);
 	g_assert (ginst->type_argv);
 
+	uint32_t h1 = ginst->type_argc;
+
 	for (guint i = 0; i < ginst->type_argc; ++i) {
-		hash *= 13;
 		g_assert (ginst->type_argv [i]);
-		hash += mono_metadata_type_hash (ginst->type_argv [i]);
+		MURMUR3_HASH_BLOCK ((uint32_t) mono_metadata_type_hash (ginst->type_argv [i]));
 	}
 
-	return hash ^ (ginst->is_open << 8);
+	h1 ^= ginst->is_open;
+
+	return (guint)murmur3_fmix32 (h1);
 }
 
 static gboolean
@@ -3494,10 +3498,9 @@ mono_metadata_get_canonical_generic_inst (MonoGenericInst *candidate)
 	mono_loader_lock ();
 
 	if (!mm->ginst_cache)
-		mm->ginst_cache = dn_simdhash_ght_new_full (mono_metadata_generic_inst_hash, mono_metadata_generic_inst_equal, NULL, (GDestroyNotify)free_generic_inst, 0, NULL);
+		mm->ginst_cache = g_hash_table_new_full (mono_metadata_generic_inst_hash, mono_metadata_generic_inst_equal, NULL, (GDestroyNotify)free_generic_inst);
 
-	MonoGenericInst *ginst = NULL;
-	dn_simdhash_ght_try_get_value (mm->ginst_cache, candidate, (void **)&ginst);
+	MonoGenericInst *ginst = g_hash_table_lookup (mm->ginst_cache, candidate);
 	if (!ginst) {
 		int size = MONO_SIZEOF_GENERIC_INST + type_argc * sizeof (MonoType *);
 		ginst = (MonoGenericInst *)mono_mem_manager_alloc0 (mm, size);
@@ -3511,7 +3514,7 @@ mono_metadata_get_canonical_generic_inst (MonoGenericInst *candidate)
 		for (int i = 0; i < type_argc; ++i)
 			ginst->type_argv [i] = mono_metadata_type_dup (NULL, candidate->type_argv [i]);
 
-		dn_simdhash_ght_insert (mm->ginst_cache, ginst, ginst);
+		g_hash_table_insert (mm->ginst_cache, ginst, ginst);
 	}
 
 	mono_loader_unlock ();