Unreachable statement in log2floor function

[iFrostizz]

There's a cleanup that can be done in the log2floor function because the

if l == 0 {

statement is unreachable.

Proof:
This branch could only be reached if value.as_limbs()[i].leading_zeros() == 64 when the loop has been iterated 4 times. But this condition is only true if value.as_limbs()[i] == 0u64, which is covered above. Meaning that the two branches are mutually exclusive.
Thus, we can just remove the statement.

diff --git a/crates/interpreter/src/gas/calc.rs b/crates/interpreter/src/gas/calc.rs
index 08ec9c0f..17330d84 100644
--- a/crates/interpreter/src/gas/calc.rs
+++ b/crates/interpreter/src/gas/calc.rs
@@ -71,12 +71,7 @@ const fn log2floor(value: U256) -> u64 {
         if value.as_limbs()[i] == 0u64 {
             l -= 64;
         } else {
-            l -= value.as_limbs()[i].leading_zeros() as u64;
-            if l == 0 {
-                return l;
-            } else {
-                return l - 1;
-            }
+            return l - value.as_limbs()[i].leading_zeros() as u64 - 1;
         }
         if i == 0 {
             break;

Tried to optimize further the hotpath by checking for zeroeness of value as a first condition which would exclude the last limb to be 0, reducing the loop iteration by one but it made the performance a little bit worse for value != 0, which makes sense:

diff --git a/crates/interpreter/src/gas/calc.rs b/crates/interpreter/src/gas/calc.rs
index 08ec9c0f..e843f6bb 100644
--- a/crates/interpreter/src/gas/calc.rs
+++ b/crates/interpreter/src/gas/calc.rs
@@ -65,25 +65,22 @@ pub const fn create2_cost(len: usize) -> Option<u64> {
 
 #[inline]
 const fn log2floor(value: U256) -> u64 {
+    if value.leading_zeros() == 256 {
+        return 0;
+    }
     let mut l: u64 = 256;
     let mut i = 3;
     loop {
         if value.as_limbs()[i] == 0u64 {
             l -= 64;
-        } else {
-            l -= value.as_limbs()[i].leading_zeros() as u64;
-            if l == 0 {
+            if i == 2 {
                 return l;
-            } else {
-                return l - 1;
             }
+            i -= 1;
+        } else {
+            return l - value.as_limbs()[i].leading_zeros() as u64 - 1;
         }
-        if i == 0 {
-            break;
-        }
-        i -= 1;
     }
-    l
 }
 
 /// `EXP` opcode cost calculation.

[iFrostizz]

Note: here is the bench used to perf for different ways of writing this function.

use std::hint::black_box;
use criterion::{criterion_group, criterion_main, Criterion};
use primitives::U256;
use revm_interpreter::gas::log2floor;

fn criterion_benchmark(c: &mut Criterion) {
    c.bench_function("log2floor 0", |b| b.iter(|| {
        for _ in 0..100_000_000 {
            log2floor(black_box(U256::ZERO));
        }
    }));

    c.bench_function("log2floor 100_000_000", |b| b.iter(|| {
        for i in 0..100_000_000 {
            log2floor(black_box(U256::from(i)));
        }
    }));
}

criterion_group!(benches, criterion_benchmark);
criterion_main!(benches);