the revive-explorer utility (#364)

A maintainable and more precise version of what was a hacky but useful
script, exploring the compilers YUL lowering unit.

It analyzes a given shared objects from the debug dump and outputs:
- The count of each YUL statement translated.
- A per YUL statement break-down of bytecode size contributed per.
- Estimated `yul-phaser` cost parameters.

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/explorer/src/yul_phaser.rs

@@ -0,0 +1,79 @@
+//! The revive explorer YUL phaser utility library.
+//!
+//! This can be used to invoke the `yul-phaser` utility,
+//! used to find better YUL optimizer sequences.
+
+use std::{
+    path::{Path, PathBuf},
+    process::{Command, Stdio},
+    thread,
+    time::{SystemTime, UNIX_EPOCH},
+};
+
+/// The `yul-phaser` sane default arguments:
+/// - Less verbose output.
+/// - Sufficient rounds.
+/// - Sufficient random population start.
+const ARGUMENTS: [&str; 6] = [
+    "--hide-round",
+    "--rounds",
+    "1000",
+    "--random-population",
+    "100",
+    "--show-only-top-chromosome",
+];
+
+/// Run multiple YUL phaser executables in parallel.
+pub fn run(
+    executable: &Path,
+    source: &Path,
+    costs: &[(String, u64)],
+    n_threads: usize,
+) -> anyhow::Result<()> {
+    let mut handles = Vec::with_capacity(n_threads);
+
+    for n in 0..n_threads {
+        let executable = executable.to_path_buf();
+        let source = source.to_path_buf();
+        let costs = costs.to_vec();
+
+        handles.push(thread::spawn(move || {
+            spawn_process(executable, source, costs, n)
+        }));
+    }
+
+    for handle in handles {
+        let _ = handle.join();
+    }
+
+    Ok(())
+}
+
+/// The `yul-phaser` process spawning helper function.
+fn spawn_process(
+    executable: PathBuf,
+    source: PathBuf,
+    costs: Vec<(String, u64)>,
+    seed: usize,
+) -> anyhow::Result<()> {
+    let cost_parameters = costs
+        .iter()
+        .flat_map(|(parameter, cost)| vec![parameter.clone(), cost.to_string()]);
+
+    let secs = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .expect("Time went backwards")
+        .as_secs();
+
+    Command::new(executable)
+        .args(cost_parameters)
+        .args(ARGUMENTS)
+        .arg("--seed")
+        .arg((seed + secs as usize).to_string())
+        .arg(source)
+        .stdin(Stdio::null())
+        .spawn()?
+        .wait()?;
+
+    Ok(())
+}