perf: save a hashing step for bytecodes (#1547)

crates/revm/src/database.rs

@@ -47,8 +47,23 @@ impl<DB: StateProvider> DatabaseRef for State<DB> {
     }
 
     fn code_by_hash(&self, code_hash: H256) -> Result<Bytecode, Self::Error> {
-        let bytecode = self.0.bytecode_by_hash(code_hash)?.unwrap_or_default();
-        Ok(Bytecode::new_raw(bytecode.0))
+        let bytecode = self.0.bytecode_by_hash(code_hash)?;
+
+        // SAFETY: We are requesting the code by its hash, so it is almost tautological why this
+        // would be safe. If the bytecode is not found, we return an empty bytecode with the
+        // appropriate hash.
+        //
+        // In an ideal world we would return analysed bytecode here, but analysed bytecode in revm
+        // depends on the current active hard fork, since it calculates gas blocks...
+        if let Some(bytecode) = bytecode {
+            Ok(unsafe { Bytecode::new_raw_with_hash(bytecode.0, code_hash) })
+        } else {
+            // NOTE(onbjerg): This corresponds to an empty analysed bytecode with a hash of
+            // `KECCAK_EMPTY`. In the case where the bytecode is not found, we would
+            // return empty bytes anyway: this simply skips the hashing and analysis steps, which
+            // would otherwise be present if we simply did an `.unwrap_or_default()` above.
+            Ok(Bytecode::new())
+        }
     }
 
     fn storage(&self, address: H160, index: U256) -> Result<U256, Self::Error> {