[mono] Extend mono_gsharedvt_constrained_call for static calls and ha…

…ndle nullable value types (dotnet#94787)

* [mono] Don't use this_arg in static constrained calls. Don't deref gsharedvt ref arguments if it is a nullable vtype.

* [mono] Fix lint formatting

* [mono] Remove additional deref register

src/mono/mono/mini/jit-icalls.c

@@ -1450,7 +1450,8 @@ mono_gsharedvt_constrained_call (gpointer mp, MonoMethod *cmethod, MonoClass *kl
 		break;
 	case MONO_GSHAREDVT_CONSTRAINT_CALL_TYPE_REF:
 		/* Calling a ref method with a ref receiver */
-		this_arg = *(gpointer*)mp;
+		/* Static calls don't have this arg */
+		this_arg = m_method_is_static (cmethod) ? NULL : *(gpointer*)mp;
 		m = info->method;
 		break;
 	default:
@@ -1482,7 +1483,8 @@ mono_gsharedvt_constrained_call (gpointer mp, MonoMethod *cmethod, MonoClass *kl
 		g_assert (fsig->param_count < 16);
 		memcpy (new_args, args, fsig->param_count * sizeof (gpointer));
 		for (int i = 0; i < fsig->param_count; ++i) {
-			if (deref_args [i])
+			// If the argument is not a vtype or nullable, deref it
+			if (deref_args [i] != MONO_GSHAREDVT_BOX_TYPE_VTYPE && deref_args [i] != MONO_GSHAREDVT_BOX_TYPE_NULLABLE)
 				new_args [i] = *(gpointer*)new_args [i];
 		}
 		args = new_args;

src/mono/mono/mini/method-to-ir.c

@@ -3896,13 +3896,8 @@ handle_constrained_gsharedvt_call (MonoCompile *cfg, MonoMethod *cmethod, MonoMe
 			int addr_reg;
 
 			if (mini_is_gsharedvt_type (fsig->params [i])) {
-				MonoInst *is_deref;
-				int deref_arg_reg;
 				ins = mini_emit_get_gsharedvt_info_klass (cfg, mono_class_from_mono_type_internal (fsig->params [i]), MONO_RGCTX_INFO_CLASS_BOX_TYPE);
-				deref_arg_reg = alloc_preg (cfg);
-				/* deref_arg = BOX_TYPE != MONO_GSHAREDVT_BOX_TYPE_VTYPE */
-				EMIT_NEW_BIALU_IMM (cfg, is_deref, OP_ISUB_IMM, deref_arg_reg, ins->dreg, 1);
-				MONO_EMIT_NEW_STORE_MEMBASE (cfg, OP_STOREI1_MEMBASE_REG, is_gsharedvt_ins->dreg, i, is_deref->dreg);
+				MONO_EMIT_NEW_STORE_MEMBASE (cfg, OP_STOREI1_MEMBASE_REG, is_gsharedvt_ins->dreg, i, ins->dreg);
 			} else if (has_gsharedvt) {
 				MONO_EMIT_NEW_STORE_MEMBASE_IMM (cfg, OP_STOREI1_MEMBASE_IMM, is_gsharedvt_ins->dreg, i, 0);
 			}