Activate new changes in TVM by version>=5, reduce gas cost for loading libraries (#875)

Co-authored-by: SpyCheese <mikle98@yandex.ru>

crypto/vm/cellops.cpp

@@ -892,34 +892,37 @@ int exec_load_special_cell(VmState* st, bool quiet) {
   Stack& stack = st->get_stack();
   VM_LOG(st) << "execute XLOAD" << (quiet ? "Q" : "");
   auto cell = stack.pop_cell();
-  auto r_loaded_cell = cell->load_cell();
-  if (r_loaded_cell.is_error()) {
-    if (quiet) {
-      stack.push_bool(false);
-      return 0;
-    } else {
-      throw VmError{Excno::cell_und, "failed to load cell"};
-    }
-  }
-  auto loaded_cell = r_loaded_cell.move_as_ok();
-  if (loaded_cell.data_cell->is_special()) {
-    if (loaded_cell.data_cell->special_type() != CellTraits::SpecialType::Library) {
+  if (st->get_global_version() >= 5) {
+    st->register_cell_load(cell->get_hash());
+    auto r_loaded_cell = cell->load_cell();
+    if (r_loaded_cell.is_error()) {
       if (quiet) {
         stack.push_bool(false);
         return 0;
       } else {
-        throw VmError{Excno::cell_und, "unexpected special cell"};
+        throw VmError{Excno::cell_und, "failed to load cell"};
       }
     }
-    CellSlice cs(std::move(loaded_cell));
-    DCHECK(cs.size() == Cell::hash_bits + 8);
-    cell = st->load_library(cs.data_bits() + 8);
-    if (cell.is_null()) {
-      if (quiet) {
-        stack.push_bool(false);
-        return 0;
-      } else {
-        throw VmError{Excno::cell_und, "failed to load library cell"};
+    auto loaded_cell = r_loaded_cell.move_as_ok();
+    if (loaded_cell.data_cell->is_special()) {
+      if (loaded_cell.data_cell->special_type() != CellTraits::SpecialType::Library) {
+        if (quiet) {
+          stack.push_bool(false);
+          return 0;
+        } else {
+          throw VmError{Excno::cell_und, "unexpected special cell"};
+        }
+      }
+      CellSlice cs(std::move(loaded_cell));
+      DCHECK(cs.size() == Cell::hash_bits + 8);
+      cell = st->load_library(cs.data_bits() + 8);
+      if (cell.is_null()) {
+        if (quiet) {
+          stack.push_bool(false);
+          return 0;
+        } else {
+          throw VmError{Excno::cell_und, "failed to load library cell"};
+        }
       }
     }
   }

crypto/vm/cells/CellSlice.cpp

@@ -1056,10 +1056,10 @@ std::ostream& operator<<(std::ostream& os, Ref<CellSlice> cs_ref) {
 // If can_be_special is not null, then it is allowed to load special cell
 // Flag whether loaded cell is actually special will be stored into can_be_special
 VirtualCell::LoadedCell load_cell_slice_impl(Ref<Cell> cell, bool* can_be_special) {
+  auto* vm_state_interface = VmStateInterface::get();
   bool library_loaded = false;
   while (true) {
-    auto* vm_state_interface = VmStateInterface::get();
-    if (vm_state_interface) {
+    if (vm_state_interface && !library_loaded) {
       vm_state_interface->register_cell_load(cell->get_hash());
     }
     auto r_loaded_cell = cell->load_cell();
@@ -1077,11 +1077,13 @@ VirtualCell::LoadedCell load_cell_slice_impl(Ref<Cell> cell, bool* can_be_specia
       *can_be_special = loaded_cell.data_cell->is_special();
     } else if (loaded_cell.data_cell->is_special()) {
       if (loaded_cell.data_cell->special_type() == DataCell::SpecialType::Library) {
-        if (library_loaded) {
-          throw VmError{Excno::cell_und, "failed to load library cell: recursive library cells are not allowed"};
-        }
-        library_loaded = true;
         if (vm_state_interface) {
+          if (vm_state_interface->get_global_version() >= 5) {
+            if (library_loaded) {
+              throw VmError{Excno::cell_und, "failed to load library cell: recursive library cells are not allowed"};
+            }
+            library_loaded = true;
+          }
           CellSlice cs(std::move(loaded_cell));
           DCHECK(cs.size() == Cell::hash_bits + 8);
           auto library_cell = vm_state_interface->load_library(cs.data_bits() + 8);

crypto/vm/vm.h

@@ -340,7 +340,7 @@ class VmState final : public VmStateInterface {
   void preclear_cr(const ControlRegs& save) {
     cr &= save;
   }
-  int get_global_version() const {
+  int get_global_version() const override {
     return global_version;
   }
   void set_global_version(int version) {

crypto/vm/vmstate.h

@@ -19,6 +19,7 @@
 #pragma once
 #include "common/refcnt.hpp"
 #include "vm/cells.h"
+#include "common/global-version.h"
 
 #include "td/utils/Context.h"
 
@@ -38,6 +39,9 @@ class VmStateInterface : public td::Context<VmStateInterface> {
   virtual bool register_op(int op_units = 1) {
     return true;
   };
+  virtual int get_global_version() const {
+    return ton::SUPPORTED_VERSION;
+  }
 };
 
 }  // namespace vm

doc/GlobalVersions.md

@@ -39,11 +39,18 @@ intermediate value before division (e.g. `(xy+w)/z`).
 * Unpaid storage fee is now saved to `due_payment`
 
 ## Version 5
+
+### Gas limits
 Version 5 enables higher gas limits for special contracts.
 
 * Gas limit for all transactions on special contracts is set to `special_gas_limit` from `ConfigParam 20` (which is 35M at the moment of writing). 
-Previously only ticktock transactions had this limit, while ordinary transactions could use up to `gas_limit` gas (1M).
+Previously only ticktock transactions had this limit, while ordinary transactions had a default limit of `gas_limit` gas (1M).
 * Gas usage of special contracts is not taken into account when checking block limits. This allows keeping masterchain block limits low
 while having high gas limits for elector.
 * Gas limit on `EQD_v9j1rlsuHHw2FIhcsCFFSD367ldfDdCKcsNmNpIRzUlu` is increased to `special_gas_limit * 2` until 2024-02-29.
-See [this post](https://t.me/tonstatus/88) for details.
+See [this post](https://t.me/tonstatus/88) for details.
+
+### Loading libraries
+* Loading "nested libraries" (i.e. a library cell that points to another library cell) throws an exception.
+* Loading a library consumes gas for cell load only once (for the library cell), not twice (both for the library cell and the cell in the library).
+* `XLOAD` now works differently. When it takes a library cell, it returns the cell that it points to. This allows loading "nested libraries", if needed.