Revert "perf: disable snapshot compression (#18061)" (#18074)

This reverts commit d12b039e1ad601622c6135e13f00fd14cb09bce1.

It was landed as an experiment and it confirms much faster startup
if not compression is applied.

1 files changed, 31 insertions, 2 deletions

diff --git a/runtime/js.rs b/runtime/js.rs
index 3101e4b6b..57b1e7be4 100644
--- a/runtime/js.rs
+++ b/runtime/js.rs
@@ -1,14 +1,43 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 #[cfg(not(feature = "dont_create_runtime_snapshot"))]
 use deno_core::Snapshot;
+#[cfg(not(feature = "dont_create_runtime_snapshot"))]
+use log::debug;
+#[cfg(not(feature = "dont_create_runtime_snapshot"))]
+use once_cell::sync::Lazy;
 
 #[cfg(not(feature = "dont_create_runtime_snapshot"))]
-static RUNTIME_SNAPSHOT: &[u8] =
+static COMPRESSED_RUNTIME_SNAPSHOT: &[u8] =
   include_bytes!(concat!(env!("OUT_DIR"), "/RUNTIME_SNAPSHOT.bin"));
 
 #[cfg(not(feature = "dont_create_runtime_snapshot"))]
+pub static RUNTIME_SNAPSHOT: Lazy<Box<[u8]>> = Lazy::new(
+  #[allow(clippy::uninit_vec)]
+  #[cold]
+  #[inline(never)]
+  || {
+    let size =
+      u32::from_le_bytes(COMPRESSED_RUNTIME_SNAPSHOT[0..4].try_into().unwrap())
+        as usize;
+    let mut vec = Vec::with_capacity(size);
+
+    // SAFETY: vec is allocated with exact snapshot size (+ alignment)
+    // SAFETY: non zeroed bytes are overwritten with decompressed snapshot
+    unsafe {
+      vec.set_len(size);
+    }
+
+    lzzzz::lz4::decompress(&COMPRESSED_RUNTIME_SNAPSHOT[4..], &mut vec)
+      .unwrap();
+
+    vec.into_boxed_slice()
+  },
+);
+
+#[cfg(not(feature = "dont_create_runtime_snapshot"))]
 pub fn deno_isolate_init() -> Snapshot {
-  Snapshot::Static(RUNTIME_SNAPSHOT)
+  debug!("Deno isolate init with snapshots.");
+  Snapshot::Static(&RUNTIME_SNAPSHOT)
 }
 
 #[cfg(not(feature = "include_js_files_for_snapshotting"))]