From b84942a0fe11c06a94cfe46ee787084e80c51fb9 Mon Sep 17 00:00:00 2001
From: Taras Tsugrii <taras.tsugriy@gmail.com>
Date: Mon, 31 Jul 2023 12:40:11 -0700
Subject: [rustc_data_structures][perf] Simplify base_n::push_str.
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This minor change removes the need to reverse resulting digits.
Since reverse is O(|digit_num|) but bounded by 128, it's unlikely
to be a noticeable in practice. At the same time, this code is
also a 1 line shorter, so combined with tiny perf win, why not?

I ran https://gist.github.com/ttsugriy/ed14860ef597ab315d4129d5f8adb191
on M1 macbook air and got a small improvement
```
Running benches/base_n_benchmark.rs (target/release/deps/base_n_benchmark-825fe5895b5c2693)
push_str/old            time:   [14.180 µs 14.313 µs 14.462 µs]
                        Performance has improved.
Found 5 outliers among 100 measurements (5.00%)
  4 (4.00%) high mild
  1 (1.00%) high severe
push_str/new            time:   [13.741 µs 13.839 µs 13.973 µs]
                        Performance has improved.
Found 8 outliers among 100 measurements (8.00%)
  3 (3.00%) high mild
  5 (5.00%) high severe
```
---
 compiler/rustc_data_structures/src/base_n.rs | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

(limited to 'compiler/rustc_data_structures/src')

diff --git a/compiler/rustc_data_structures/src/base_n.rs b/compiler/rustc_data_structures/src/base_n.rs
index 4567759c004..58704350706 100644
--- a/compiler/rustc_data_structures/src/base_n.rs
+++ b/compiler/rustc_data_structures/src/base_n.rs
@@ -16,22 +16,21 @@ const BASE_64: &[u8; MAX_BASE] =
 pub fn push_str(mut n: u128, base: usize, output: &mut String) {
     debug_assert!(base >= 2 && base <= MAX_BASE);
     let mut s = [0u8; 128];
-    let mut index = 0;
+    let mut index = s.len();
 
     let base = base as u128;
 
     loop {
+        index -= 1;
         s[index] = BASE_64[(n % base) as usize];
-        index += 1;
         n /= base;
 
         if n == 0 {
             break;
         }
     }
-    s[0..index].reverse();
 
-    output.push_str(str::from_utf8(&s[0..index]).unwrap());
+    output.push_str(str::from_utf8(&s[index..]).unwrap());
 }
 
 #[inline]
-- 
cgit 1.4.1-3-g733a5


From 3eb5733ed4799dd636432f5080dd62cf2d401ab7 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 31 Jul 2023 09:50:44 +0000
Subject: Always use parking_lot's RwLock, even without parallel compiler

---
 compiler/rustc_data_structures/src/sync/vec.rs | 28 +++++++-------------------
 1 file changed, 7 insertions(+), 21 deletions(-)

(limited to 'compiler/rustc_data_structures/src')

diff --git a/compiler/rustc_data_structures/src/sync/vec.rs b/compiler/rustc_data_structures/src/sync/vec.rs
index e36dded9e5e..314496ce9f0 100644
--- a/compiler/rustc_data_structures/src/sync/vec.rs
+++ b/compiler/rustc_data_structures/src/sync/vec.rs
@@ -43,37 +43,23 @@ impl<I: Idx, T: Copy> AppendOnlyIndexVec<I, T> {
 
 #[derive(Default)]
 pub struct AppendOnlyVec<T: Copy> {
-    #[cfg(not(parallel_compiler))]
-    vec: elsa::vec::FrozenVec<T>,
-    #[cfg(parallel_compiler)]
-    vec: elsa::sync::LockFreeFrozenVec<T>,
+    vec: parking_lot::RwLock<Vec<T>>,
 }
 
 impl<T: Copy> AppendOnlyVec<T> {
     pub fn new() -> Self {
-        Self {
-            #[cfg(not(parallel_compiler))]
-            vec: elsa::vec::FrozenVec::new(),
-            #[cfg(parallel_compiler)]
-            vec: elsa::sync::LockFreeFrozenVec::new(),
-        }
+        Self { vec: Default::default() }
     }
 
     pub fn push(&self, val: T) -> usize {
-        #[cfg(not(parallel_compiler))]
-        let i = self.vec.len();
-        #[cfg(not(parallel_compiler))]
-        self.vec.push(val);
-        #[cfg(parallel_compiler)]
-        let i = self.vec.push(val);
-        i
+        let mut v = self.vec.write();
+        let n = v.len();
+        v.push(val);
+        n
     }
 
     pub fn get(&self, i: usize) -> Option<T> {
-        #[cfg(not(parallel_compiler))]
-        return self.vec.get_copy(i);
-        #[cfg(parallel_compiler)]
-        return self.vec.get(i);
+        self.vec.read().get(i).copied()
     }
 
     pub fn iter_enumerated(&self) -> impl Iterator<Item = (usize, T)> + '_ {
-- 
cgit 1.4.1-3-g733a5