From a0376d361b83360c6f9eb971419726995f4c9c19 Mon Sep 17 00:00:00 2001
From: Jonas Maier <jonas@x77.dev>
Date: Sat, 6 Jun 2026 21:11:02 +0200
Subject: regex: perf improvement by using ops that do not free and alloc again

---
 src/regex/bc.rs | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

(limited to 'src')

diff --git a/src/regex/bc.rs b/src/regex/bc.rs
index 5de1513..ea1d086 100644
--- a/src/regex/bc.rs
+++ b/src/regex/bc.rs
@@ -114,8 +114,8 @@ struct Thread<F: Flavor> {
 
 struct VM<'p, F: Flavor> {
     instr: &'p [Instr<F>],
-    passive_threads: VecDeque<Thread<F>>,
-    active_threads: VecDeque<Thread<F>>,
+    passive_threads: Vec<Thread<F>>,
+    active_threads: Vec<Thread<F>>,
     hot: BitSet,
     warm: BitSet,
 }
@@ -124,8 +124,8 @@ impl<'p, F: Flavor> VM<'p, F> {
     fn new(instr: &'p [Instr<F>], starting_thread: Thread<F>) -> Self {
         Self {
             instr,
-            passive_threads: vec![starting_thread].into(),
-            active_threads: VecDeque::new(),
+            passive_threads: vec![starting_thread],
+            active_threads: Vec::new(),
             hot: BitSet::new(instr.len()),
             warm: BitSet::new(instr.len()),
         }
@@ -142,7 +142,7 @@ impl<'p, F: Flavor> VM<'p, F> {
                 let bit = t.pc as usize;
                 if !self.warm.get(bit) {
                     self.warm.set(bit, true);
-                    self.active_threads.push_front(t);
+                    self.active_threads.push(t);
                 }
             }};
         }
@@ -157,13 +157,13 @@ impl<'p, F: Flavor> VM<'p, F> {
             }};
         }
 
-        while let Some(mut thread) = self.active_threads.pop_front() {
+        while let Some(mut thread) = self.active_threads.pop() {
             loop {
                 match self.instr[thread.pc as usize] {
                     Instr::Class(_) | Instr::Consume(_) => {
                         if !self.hot.get(thread.pc as usize) {
                             self.hot.set(thread.pc as usize, true);
-                            self.passive_threads.push_back(thread);
+                            self.passive_threads.push(thread);
                         }
                     }
                     Instr::Jump(j) => {
@@ -188,6 +188,8 @@ impl<'p, F: Flavor> VM<'p, F> {
                 break;
             }
         }
+
+        self.passive_threads.reverse();
     }
 
     fn step_consume(&mut self, byte: u8) {
-- 
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