fuzz: count successful executions of differential_spec target

fuzz/fuzz_targets/differential_spec.rs

@@ -1,13 +1,31 @@
 #![no_main]
 
 use libfuzzer_sys::fuzz_target;
+use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
 use wasmtime_fuzzing::{generators, oracles};
 
+// Keep track of how many WebAssembly modules we actually executed (i.e. ran to
+// completion) versus how many were tried.
+static TRIED: AtomicUsize = AtomicUsize::new(0);
+static EXECUTED: AtomicUsize = AtomicUsize::new(0);
+
 fuzz_target!(|data: (
     generators::Config,
     wasm_smith::ConfiguredModule<oracles::SingleFunctionModuleConfig>
 )| {
     let (config, mut wasm) = data;
     wasm.ensure_termination(1000);
-    oracles::differential_spec_execution(&wasm.to_bytes(), &config);
+    let tried = TRIED.fetch_add(1, SeqCst);
+    let executed = match oracles::differential_spec_execution(&wasm.to_bytes(), &config) {
+        Some(_) => EXECUTED.fetch_add(1, SeqCst),
+        None => EXECUTED.load(SeqCst),
+    };
+    if tried > 0 && tried % 1000 == 0 {
+        println!(
+            "=== Execution rate ({} executed modules / {} tried modules): {}% ===",
+            executed,
+            tried,
+            executed as f64 / tried as f64 * 100f64
+        )
+    }
 });