perf(levm): use unchecked swap

CHANGELOG.md

@@ -7,6 +7,10 @@
 - Change some calls from `encode_to_vec().len()` to `.length()` when wanting to get the rlp encoded length [#5374](https://github.com/lambdaclass/ethrex/pull/5374)
 - Use our keccak implementation for receipts bloom filter calculation [#5454](https://github.com/lambdaclass/ethrex/pull/5454)
 
+### 2025-11-27
+
+- Use unchecked swap for stack [#5439](https://github.com/lambdaclass/ethrex/pull/5439)
+
 ### 2025-11-20
 
 - Improve rlp encoding by avoiding extra loops and remove unneeded array vec, also adding a alloc-less length method the default trait impl [#5350](https://github.com/lambdaclass/ethrex/pull/5350)

crates/vm/levm/src/call_frame.rs

@@ -9,7 +9,7 @@ use crate::{
 use bytes::Bytes;
 use ethrex_common::{Address, U256};
 use ethrex_common::{H256, types::Code};
-use std::{collections::HashMap, fmt};
+use std::{collections::HashMap, fmt, hint::assert_unchecked};
 
 /// [`u64`]s that make up a [`U256`]
 const U64_PER_U256: usize = U256::MAX.0.len();
@@ -148,6 +148,11 @@ impl Stack {
             return Err(ExceptionalHalt::StackUnderflow);
         }
 
+        #[expect(unsafe_code, reason = "self.offset always < STACK_LIMIT")]
+        unsafe {
+            assert_unchecked(self.offset < STACK_LIMIT)
+        };
+
         self.values.swap(self.offset, index);
         Ok(())
     }