diff --git a/src/Psalm/Internal/Codebase/Functions.php b/src/Psalm/Internal/Codebase/Functions.php
index 1861e3239..c88fb2988 100644
--- a/src/Psalm/Internal/Codebase/Functions.php
+++ b/src/Psalm/Internal/Codebase/Functions.php
@@ -346,6 +346,11 @@ class Functions
             return false;
         }
 
+        // $matches is basically the (conditional) output of these functions
+        if ($function_id === 'preg_match' || $function_id === 'preg_match_all') {
+            return true;
+        }
+
         $function_callable = \Psalm\Internal\Codebase\CallMap::getCallableFromCallMapById(
             $codebase,
             $function_id,
@@ -356,12 +361,6 @@ class Functions
             return false;
         }
 
-        foreach ($function_callable->params as $i => $param) {
-            if ($param->by_ref && isset($args[$i])) {
-                return false;
-            }
-        }
-
         return true;
     }
 
diff --git a/src/Psalm/Internal/Stubs/CoreGenericFunctions.php b/src/Psalm/Internal/Stubs/CoreGenericFunctions.php
index a35daa9e6..81072aa79 100644
--- a/src/Psalm/Internal/Stubs/CoreGenericFunctions.php
+++ b/src/Psalm/Internal/Stubs/CoreGenericFunctions.php
@@ -7,6 +7,7 @@
  * @param bool            $strict
  *
  * @return array<int, T>
+ * @psalm-pure
  */
 function array_keys(array $arr, $search_value = null, bool $strict = false)
 {
@@ -18,6 +19,7 @@ function array_keys(array $arr, $search_value = null, bool $strict = false)
  * @param array<mixed, T> $arr
  *
  * @return array<int, T>
+ * @psalm-pure
  */
 function array_values(array $arr)
 {
@@ -31,6 +33,7 @@ function array_values(array $arr)
  * @param int $sort_flags
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_unique(array $arr, int $sort_flags = 0)
 {
@@ -46,6 +49,7 @@ function array_unique(array $arr, int $sort_flags = 0)
  * @param array|null $arr4
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_intersect(array $arr, array $arr2, array $arr3 = null, array $arr4 = null)
 {
@@ -61,6 +65,7 @@ function array_intersect(array $arr, array $arr2, array $arr3 = null, array $arr
  * @param array|null $arr4
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_intersect_key(array $arr, array $arr2, array $arr3 = null, array $arr4 = null)
 {
@@ -75,6 +80,7 @@ function array_intersect_key(array $arr, array $arr2, array $arr3 = null, array
  *
  * @return array<TKey, TValue>|false
  * @psalm-ignore-falsable-return
+ * @psalm-pure
  */
 function array_combine(array $arr, array $arr2)
 {
@@ -90,6 +96,7 @@ function array_combine(array $arr, array $arr2)
  * @param array|null $arr4
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_diff(array $arr, array $arr2, array $arr3 = null, array $arr4 = null)
 {
@@ -105,6 +112,7 @@ function array_diff(array $arr, array $arr2, array $arr3 = null, array $arr4 = n
  * @param array|null $arr4
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_diff_key(array $arr, array $arr2, array $arr3 = null, array $arr4 = null)
 {
@@ -117,6 +125,7 @@ function array_diff_key(array $arr, array $arr2, array $arr3 = null, array $arr4
  * @param array<TKey, TValue> $arr
  *
  * @return array<TValue, TKey>
+ * @psalm-pure
  */
 function array_flip(array $arr)
 {
@@ -129,6 +138,7 @@ function array_flip(array $arr)
  *
  * @return TKey|null
  * @psalm-ignore-nullable-return
+ * @psalm-pure
  */
 function key($arr)
 {
@@ -140,6 +150,7 @@ function key($arr)
  * @param TValue $value
  *
  * @return array<int, TValue>
+ * @psalm-pure
  */
 function array_fill(int $start_index, int $num, $value) : array
 {
@@ -153,6 +164,7 @@ function array_fill(int $start_index, int $num, $value) : array
  * @param bool            $strict
  *
  * @return T|false
+ * @psalm-pure
  */
 function array_search($needle, array $haystack, bool $strict = false)
 {
@@ -164,6 +176,7 @@ function array_search($needle, array $haystack, bool $strict = false)
  * @param array<mixed,T> $arr
  * @param callable(T,T):int $callback
  * @param-out array<int,T> $arr
+ * @psalm-pure
  */
 function usort(array &$arr, callable $callback): bool
 {
@@ -175,6 +188,7 @@ function usort(array &$arr, callable $callback): bool
  * @param array<string, T> $arr
  *
  * @return array<string, T>
+ * @psalm-pure
  */
 function array_change_key_case(array $arr, int $case = CASE_LOWER)
 {
@@ -186,6 +200,7 @@ function array_change_key_case(array $arr, int $case = CASE_LOWER)
  * @param array<array-key, T> $arr
  *
  * @return array<int, array<array-key, T>>
+ * @psalm-pure
  */
 function array_chunk(array $arr, int $size, bool $preserve_keys = false)
 {
@@ -198,6 +213,7 @@ function array_chunk(array $arr, int $size, bool $preserve_keys = false)
  * @param array<TKey, mixed> $search
  *
  * @return bool
+ * @psalm-pure
  */
 function array_key_exists($key, array $search) : bool
 {
@@ -211,6 +227,7 @@ function array_key_exists($key, array $search) : bool
  * @param array<TKey, TValue> ...$arr2
  *
  * @return array<TKey, TValue>
+ * @psalm-pure
  */
 function array_merge_recursive(array $arr, array ...$arr2)
 {