diff --git a/src/Psalm/Internal/Algebra.php b/src/Psalm/Internal/Algebra.php
index f60f76446b1..7b59a0af77e 100644
--- a/src/Psalm/Internal/Algebra.php
+++ b/src/Psalm/Internal/Algebra.php
@@ -136,6 +136,7 @@ public static function simplifyCNF(array $clauses): array
             if (!$clause_a->reconcilable || $clause_a->wedge) {
                 continue;
             }
+            $clause_a_keys = array_keys($clause_a->possibilities);
 
             if (count($clause_a->possibilities) !== 1 || count(array_values($clause_a->possibilities)[0]) !== 1) {
                 foreach ($cloned_clauses as $clause_b) {
@@ -143,7 +144,7 @@ public static function simplifyCNF(array $clauses): array
                         continue;
                     }
 
-                    if (array_keys($clause_a->possibilities) === array_keys($clause_b->possibilities)) {
+                    if ($clause_a_keys === array_keys($clause_b->possibilities)) {
                         $opposing_keys = [];
 
                         foreach ($clause_a->possibilities as $key => $a_possibilities) {
diff --git a/src/Psalm/Internal/Clause.php b/src/Psalm/Internal/Clause.php
index f861487c2cf..7996923015e 100644
--- a/src/Psalm/Internal/Clause.php
+++ b/src/Psalm/Internal/Clause.php
@@ -10,15 +10,17 @@
 use function array_unique;
 use function array_values;
 use function count;
+use function hash;
 use function implode;
 use function ksort;
-use function md5;
 use function reset;
 use function serialize;
 use function sort;
 use function strpos;
 use function substr;
 
+use const PHP_VERSION_ID;
+
 /**
  * @internal
  *
@@ -106,11 +108,15 @@ public function __construct(
         } else {
             ksort($possibilities);
 
-            foreach ($possibilities as $i => $_) {
+            foreach ($possibilities as $i => $v) {
+                if (count($v) < 2) {
+                    continue;
+                }
                 sort($possibilities[$i]);
             }
 
-            $this->hash = md5(serialize($possibilities));
+            $data = serialize($possibilities);
+            $this->hash = PHP_VERSION_ID >= 80100 ? hash('xxh128', $data) : hash('md4', $data);
         }
     }
 
@@ -120,8 +126,14 @@ public function contains(Clause $other_clause): bool
             return false;
         }
 
+        foreach ($other_clause->possibilities as $var => $_) {
+            if (!isset($this->possibilities[$var])) {
+                return false;
+            }
+        }
+
         foreach ($other_clause->possibilities as $var => $possible_types) {
-            if (!isset($this->possibilities[$var]) || count(array_diff($possible_types, $this->possibilities[$var]))) {
+            if (count(array_diff($possible_types, $this->possibilities[$var]))) {
                 return false;
             }
         }
diff --git a/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php b/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php
index 0c79452a647..dae227f5520 100644
--- a/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php
+++ b/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php
@@ -17,6 +17,7 @@
 use function igbinary_serialize;
 use function igbinary_unserialize;
 use function is_dir;
+use function is_null;
 use function mkdir;
 use function serialize;
 use function strtolower;
@@ -75,9 +76,15 @@ public function writeToCache(ClassLikeStorage $storage, string $file_path, strin
     {
         $fq_classlike_name_lc = strtolower($storage->name);
 
-        $cache_location = $this->getCacheLocationForClass($fq_classlike_name_lc, $file_path, true);
         $storage->hash = $this->getCacheHash($file_path, $file_contents);
 
+        // check if we have it in cache already
+        $cached_value = $this->loadFromCache($fq_classlike_name_lc, $file_path);
+        if (!is_null($cached_value) && $cached_value->hash === $storage->hash) {
+            return;
+        }
+
+        $cache_location = $this->getCacheLocationForClass($fq_classlike_name_lc, $file_path, true);
         if ($this->config->use_igbinary) {
             file_put_contents($cache_location, igbinary_serialize($storage));
         } else {
@@ -110,9 +117,9 @@ public function getLatestFromCache(
         return $cached_value;
     }
 
-    private function getCacheHash(?string $file_path, ?string $file_contents): string
+    private function getCacheHash(?string $_unused_file_path, ?string $file_contents): string
     {
-        $data = ($file_path ? $file_contents : '') . $this->modified_timestamps;
+        $data = $file_contents ? $file_contents : $this->modified_timestamps;
         return PHP_VERSION_ID >= 80100 ? hash('xxh128', $data) : hash('md4', $data);
     }
 
diff --git a/src/Psalm/Internal/Provider/FileStorageCacheProvider.php b/src/Psalm/Internal/Provider/FileStorageCacheProvider.php
index 5d4a5b29b0d..d52b4165acf 100644
--- a/src/Psalm/Internal/Provider/FileStorageCacheProvider.php
+++ b/src/Psalm/Internal/Provider/FileStorageCacheProvider.php
@@ -117,9 +117,12 @@ public function removeCacheForFile(string $file_path): void
         }
     }
 
-    private function getCacheHash(string $file_path, string $file_contents): string
+    private function getCacheHash(string $_unused_file_path, string $file_contents): string
     {
-        $data = ($file_path ? $file_contents : '') . $this->modified_timestamps;
+        // do not concatenate, as $file_contents can be big and performance will be bad
+        // the timestamp is only needed if we don't have file contents
+        // as same contents should give same results, independent of when file was modified
+        $data = $file_contents ? $file_contents : $this->modified_timestamps;
         return PHP_VERSION_ID >= 80100 ? hash('xxh128', $data) : hash('md4', $data);
     }