[mono] Simplify of OffsetToStringData as it's done on coreclr

src/mono/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.Mono.cs

@@ -32,8 +32,20 @@
         [Obsolete("OffsetToStringData has been deprecated. Use string.GetPinnableReference() instead.")]
         public static int OffsetToStringData
         {
-            [Intrinsic]
-            get => OffsetToStringData;
+            [NonVersionable]
+            get =>
+                // Number of bytes from the address pointed to by a reference to
+                // a String to the first 16-bit character in the String.  Skip
+                // over the MethodTable pointer, & String
+                // length.  Of course, the String reference points to the memory
+                // after the sync block, so don't count that.
+                // This property allows C#'s fixed statement to work on Strings.
+                // On 64 bit platforms, this should be 12 (8+4) and on 32 bit 8 (4+4).
+#if TARGET_64BIT
+                20;
+#else // 32
+                12;
+#endif // TARGET_64BIT
         }
 
         [MethodImplAttribute(MethodImplOptions.InternalCall)]

src/mono/mono/mini/interp/transform.c

@@ -2305,16 +2305,7 @@ interp_handle_intrinsics (TransformData *td, MonoMethod *target_method, MonoClas
 			*op = MINT_INITBLK;
 		}
 	} else if (in_corlib && !strcmp (klass_name_space, "System.Runtime.CompilerServices") && !strcmp (klass_name, "RuntimeHelpers")) {
-		if (!strcmp (tm, "get_OffsetToStringData")) {
-			g_assert (csignature->param_count == 0);
-			int offset = MONO_STRUCT_OFFSET (MonoString, chars);
-			interp_add_ins (td, MINT_LDC_I4);
-			WRITE32_INS (td->last_ins, 0, &offset);
-			push_simple_type (td, STACK_TYPE_I4);
-			interp_ins_set_dreg (td->last_ins, td->sp [-1].local);
-			td->ip += 5;
-			return TRUE;
-		} else if (!strcmp (tm, "GetHashCode") || !strcmp (tm, "InternalGetHashCode")) {
+		if (!strcmp (tm, "GetHashCode") || !strcmp (tm, "InternalGetHashCode")) {
 			*op = MINT_INTRINS_GET_HASHCODE;
 		} else if (!strcmp (tm, "TryGetHashCode")) {
 			*op = MINT_INTRINS_TRY_GET_HASHCODE;

src/mono/mono/mini/intrinsics.c

@@ -935,10 +935,7 @@ mini_emit_inst_for_method (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSign
 		} else
 			return NULL;
 	} else if (cmethod->klass == runtime_helpers_class) {
-		if (strcmp (cmethod->name, "get_OffsetToStringData") == 0 && fsig->param_count == 0) {
-			EMIT_NEW_ICONST (cfg, ins, MONO_STRUCT_OFFSET (MonoString, chars));
-			return ins;
-		} else if (!strcmp (cmethod->name, "GetRawData")) {
+		if (!strcmp (cmethod->name, "GetRawData")) {
 			int dreg = alloc_preg (cfg);
 			EMIT_NEW_BIALU_IMM (cfg, ins, OP_PADD_IMM, dreg, args [0]->dreg, MONO_ABI_SIZEOF (MonoObject));
 			return ins;