From c0223befe145905f5a9ffb82d967930367e3d837 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Tue, 9 Sep 2025 15:22:36 +0200
Subject: [PATCH] LibWasm: Avoid frequent re/deallocations while validating
 expressions

Freeing and reallocating these vectors was ~6% of runtime when
validating some web-based game.
---
 .../LibWasm/AbstractMachine/AbstractMachine.h      |  2 +-
 Libraries/LibWasm/AbstractMachine/Validator.h      | 14 ++++++++------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/Libraries/LibWasm/AbstractMachine/AbstractMachine.h b/Libraries/LibWasm/AbstractMachine/AbstractMachine.h
index 24bc924a1a..0fd54a8101 100644
--- a/Libraries/LibWasm/AbstractMachine/AbstractMachine.h
+++ b/Libraries/LibWasm/AbstractMachine/AbstractMachine.h
@@ -622,7 +622,7 @@ public:
 
 private:
     ModuleInstance const& m_module;
-    Vector<Value> m_locals;
+    Vector<Value, 8> m_locals;
     Expression const& m_expression;
     size_t m_arity { 0 };
     size_t m_label_index { 0 };
diff --git a/Libraries/LibWasm/AbstractMachine/Validator.h b/Libraries/LibWasm/AbstractMachine/Validator.h
index 69d59fd985..7d348f11ac 100644
--- a/Libraries/LibWasm/AbstractMachine/Validator.h
+++ b/Libraries/LibWasm/AbstractMachine/Validator.h
@@ -206,7 +206,9 @@ public:
         friend struct AK::Formatter;
 
     public:
-        explicit Stack(Vector<Frame> const& frames)
+        explicit Stack(Vector<Frame, 16>&&) = delete;
+
+        explicit Stack(Vector<Frame, 16> const& frames)
             : m_frames(frames)
         {
         }
@@ -261,17 +263,17 @@ public:
             return {};
         }
 
-        Vector<StackEntry> release_vector()
+        Vector<StackEntry, 8> release_vector()
         {
             m_max_known_size = 0;
-            return exchange(m_entries, Vector<StackEntry> {});
+            return exchange(m_entries, {});
         }
 
         size_t max_known_size() const { return m_max_known_size; }
 
     private:
-        Vector<StackEntry> m_entries;
-        Vector<Frame> const& m_frames;
+        Vector<StackEntry, 8> m_entries;
+        Vector<Frame, 16> const& m_frames;
         size_t m_max_known_size { 0 };
     };
 
@@ -360,7 +362,7 @@ private:
     };
 
     Context m_context;
-    Vector<Frame> m_frames;
+    Vector<Frame, 16> m_frames;
     size_t m_max_frame_size { 0 };
     COWVector<GlobalType> m_globals_without_internal_globals;
 };