Fix decommit operation handler

src/decommit.rs

@@ -77,11 +77,12 @@ impl WorldDiff {
         Some((UnpaidDecommit { cost, code_key }, is_evm))
     }
 
-    pub(crate) fn decommit_opcode(&mut self, world: &mut dyn World, code_hash: U256) -> Vec<u8> {
-        let mut code_info_bytes = [0; 32];
-        code_hash.to_big_endian(&mut code_info_bytes);
-        self.decommitted_hashes.insert(code_hash, ());
-        world.decommit_code(code_hash)
+    /// Returns the decommitted contract code and a flag set to `true` if this is a fresh decommit (i.e.,
+    /// the code wasn't decommitted previously in the same VM run).
+    #[doc(hidden)] // should be used for testing purposes only; can break VM operation otherwise
+    pub fn decommit_opcode(&mut self, world: &mut dyn World, code_hash: U256) -> (Vec<u8>, bool) {
+        let was_decommitted = self.decommitted_hashes.insert(code_hash, ()).is_some();
+        (world.decommit_code(code_hash), !was_decommitted)
     }
 
     pub(crate) fn pay_for_decommit(

src/instruction_handlers/decommit.rs

@@ -33,7 +33,10 @@ fn decommit(
             return;
         }
 
-        let program = vm.world_diff.decommit_opcode(world, code_hash);
+        let (program, is_fresh) = vm.world_diff.decommit_opcode(world, code_hash);
+        if !is_fresh {
+            vm.state.current_frame.gas += extra_cost;
+        }
 
         let heap = vm.state.heaps.allocate();
         vm.state.current_frame.heaps_i_am_keeping_alive.push(heap);
@@ -49,6 +52,7 @@ fn decommit(
         Register1::set_fat_ptr(args, &mut vm.state, value);
     })
 }
+
 impl Instruction {
     pub fn from_decommit(
         abi: Register1,