fix: instruction count diff always N/A in VM perf comparison (#1608)

Instruction count diff should now be correct. The problem wasn't found
initially because counting instructions legitimately fails if the PR
starts from a version where that wasn't supported yet.

Also found and fixed a bug that hid performance improvements.

.github/workflows/vm-perf-comparison.yml

@@ -46,7 +46,7 @@ jobs:
           ci_run zk
           ci_run zk compiler system-contracts
           ci_run cargo bench --package vm-benchmark --bench iai | tee base-iai
-          ci_run cd core/tests/vm_benchmark && cargo run --release --bin instruction-counts | tee base-opcodes || touch base-opcodes
+          ci_run cargo run --package vm-benchmark --release --bin instruction-counts | tee base-opcodes || touch base-opcodes
           ci_run yarn workspace system-contracts clean
 
       - name: checkout PR
@@ -58,7 +58,7 @@ jobs:
           ci_run zk
           ci_run zk compiler system-contracts
           ci_run cargo bench --package vm-benchmark --bench iai | tee pr-iai
-          ci_run cd core/tests/vm_benchmark && cargo run --release --bin instruction-counts | tee pr-opcodes || touch pr-opcodes
+          ci_run cargo run --package vm-benchmark --release --bin instruction-counts | tee pr-opcodes || touch pr-opcodes
 
           EOF=$(dd if=/dev/urandom bs=15 count=1 status=none | base64)
           echo "speedup<<$EOF" >> $GITHUB_OUTPUT

core/tests/vm-benchmark/src/compare_iai_results.rs

@@ -25,7 +25,7 @@ fn main() {
         .intersection(&iai_after.keys().collect())
         .flat_map(|&name| {
             let diff = percent_difference(iai_before[name], iai_after[name]);
-            if diff > 2. {
+            if diff.abs() > 2. {
                 Some((name, format!("{:+.1}%", diff)))
             } else {
                 None

core/tests/vm-benchmark/src/instruction_counts.rs

@@ -1,9 +1,19 @@
 //! Runs all benchmarks and prints out the number of zkEVM opcodes each one executed.
 
+use std::path::Path;
+
 use vm_benchmark_harness::{cut_to_allowed_bytecode_size, get_deploy_tx, BenchmarkingVm};
 
 fn main() {
-    for path in std::fs::read_dir("deployment_benchmarks").unwrap() {
+    // using source file location because this is just a script, the binary isn't meant to be reused
+    let benchmark_folder = Path::new(file!())
+        .parent()
+        .unwrap()
+        .parent()
+        .unwrap()
+        .join("deployment_benchmarks");
+
+    for path in std::fs::read_dir(benchmark_folder).unwrap() {
         let path = path.unwrap().path();
 
         let test_contract = std::fs::read(&path).expect("failed to read file");