From 0e8fc4dc6cc5bb089be56bda4935b24e0dc5328f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bartek=20Iwa=C5=84czuk?= <biwanczuk@gmail.com>
Date: Wed, 8 Mar 2023 11:44:04 -0400
Subject: 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.
---
 cli/js.rs | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

(limited to 'cli/js.rs')

diff --git a/cli/js.rs b/cli/js.rs
index f3c4fea68..06a6a5fd9 100644
--- a/cli/js.rs
+++ b/cli/js.rs
@@ -1,12 +1,37 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 
 use deno_core::Snapshot;
+use log::debug;
+use once_cell::sync::Lazy;
 
-static CLI_SNAPSHOT: &[u8] =
-  include_bytes!(concat!(env!("OUT_DIR"), "/CLI_SNAPSHOT.bin"));
+pub static CLI_SNAPSHOT: Lazy<Box<[u8]>> = Lazy::new(
+  #[allow(clippy::uninit_vec)]
+  #[cold]
+  #[inline(never)]
+  || {
+    static COMPRESSED_CLI_SNAPSHOT: &[u8] =
+      include_bytes!(concat!(env!("OUT_DIR"), "/CLI_SNAPSHOT.bin"));
+
+    let size =
+      u32::from_le_bytes(COMPRESSED_CLI_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_CLI_SNAPSHOT[4..], &mut vec).unwrap();
+
+    vec.into_boxed_slice()
+  },
+);
 
 pub fn deno_isolate_init() -> Snapshot {
-  Snapshot::Static(CLI_SNAPSHOT)
+  debug!("Deno isolate init with snapshots.");
+  Snapshot::Static(&CLI_SNAPSHOT)
 }
 
 #[cfg(test)]
-- 
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