Improve the hash function used in the InstMethodHashTable (#95285)

Instead of using the TypeDef token of the MethodTable, use the TypeHandle pointer instead. This is both faster to compute, and is more unique, as the TypeDef token could be shared across multiple types in different assemblies, and if the type is generic itself, it could be shared across multiple different instantiations of the type.

Improves the benchmark mentioned in isseu #94936 such that the cost is about 24 seconds, and the time in spent is spent almost entirely in the JIT, as should be expected.

Fixes #94936

Co-authored-by: David Wrighton <[email protected]>

src/coreclr/vm/instmethhash.cpp

@@ -96,30 +96,19 @@ static DWORD Hash(TypeHandle declaringType, mdMethodDef token, Instantiation ins
 
     DWORD dwHash = 0x87654321;
 #define INST_HASH_ADD(_value) dwHash = ((dwHash << 5) + dwHash) ^ (_value)
+#ifdef TARGET_64BIT
+#define INST_HASH_ADDPOINTER(_value) INST_HASH_ADD((uint32_t)(uintptr_t)_value); INST_HASH_ADD((uint32_t)(((uintptr_t)_value) >> 32))
+#else
+#define INST_HASH_ADDPOINTER(_value) INST_HASH_ADD((uint32_t)(uintptr_t)_value);
+#endif
 
-    INST_HASH_ADD(declaringType.GetCl());
+    INST_HASH_ADDPOINTER(declaringType.AsPtr());
     INST_HASH_ADD(token);
 
     for (DWORD i = 0; i < inst.GetNumArgs(); i++)
     {
         TypeHandle thArg = inst[i];
-
-        if (thArg.GetMethodTable())
-        {
-            INST_HASH_ADD(thArg.GetCl());
-
-            Instantiation sArgInst = thArg.GetInstantiation();
-            for (DWORD j = 0; j < sArgInst.GetNumArgs(); j++)
-            {
-                TypeHandle thSubArg = sArgInst[j];
-                if (thSubArg.GetMethodTable())
-                    INST_HASH_ADD(thSubArg.GetCl());
-                else
-                    INST_HASH_ADD(thSubArg.GetSignatureCorElementType());
-            }
-        }
-        else
-            INST_HASH_ADD(thArg.GetSignatureCorElementType());
+        INST_HASH_ADDPOINTER(thArg.AsPtr());
     }
 
     return dwHash;