diff --git a/src/Fixer/FunctionNotation/NativeFunctionInvocationFixer.php b/src/Fixer/FunctionNotation/NativeFunctionInvocationFixer.php
index 95e3e0c60e1..f719968e5f1 100644
--- a/src/Fixer/FunctionNotation/NativeFunctionInvocationFixer.php
+++ b/src/Fixer/FunctionNotation/NativeFunctionInvocationFixer.php
@@ -380,17 +380,22 @@ private function getAllCompilerOptimizedFunctionsNormalized(): array
             'is_object',
             'is_real',
             'is_resource',
+            'is_scalar',
             'is_string',
             'ord',
+            'sizeof',
             'strlen',
             'strval',
             // @see https://github.com/php/php-src/blob/php-7.2.6/ext/opcache/Optimizer/pass1_5.c
+            // @see https://github.com/php/php-src/blob/PHP-8.1.2/Zend/Optimizer/block_pass.c
+            // @see https://github.com/php/php-src/blob/php-8.1.3/Zend/Optimizer/zend_optimizer.c
             'constant',
             'define',
             'dirname',
             'extension_loaded',
             'function_exists',
             'is_callable',
+            'ini_get',
         ]);
     }
 
diff --git a/tests/Fixer/PhpTag/NoClosingTagFixerTest.php b/tests/Fixer/PhpTag/NoClosingTagFixerTest.php
index 97113cf856e..ce86849d7e5 100644
--- a/tests/Fixer/PhpTag/NoClosingTagFixerTest.php
+++ b/tests/Fixer/PhpTag/NoClosingTagFixerTest.php
@@ -36,7 +36,7 @@ public function testWithFullOpenTag(string $expected, ?string $input = null): vo
      */
     public function testWithShortOpenTag(string $expected, ?string $input = null): void
     {
-        if (!ini_get('short_open_tag')) {
+        if (!\ini_get('short_open_tag')) {
             static::markTestSkipped('The short_open_tag option is required to be enabled.');
         }
 
diff --git a/tests/Fixer/Semicolon/NoEmptyStatementFixerTest.php b/tests/Fixer/Semicolon/NoEmptyStatementFixerTest.php
index 6a0baba348e..83e4bb4ce03 100644
--- a/tests/Fixer/Semicolon/NoEmptyStatementFixerTest.php
+++ b/tests/Fixer/Semicolon/NoEmptyStatementFixerTest.php
@@ -521,7 +521,7 @@ public function log($msg)
      */
     public function testCasesWithShortOpenTag(string $expected, ?string $input = null): void
     {
-        if (!ini_get('short_open_tag')) {
+        if (!\ini_get('short_open_tag')) {
             static::markTestSkipped('No short tag tests possible.');
         }
 
diff --git a/tests/Fixer/Semicolon/SemicolonAfterInstructionFixerTest.php b/tests/Fixer/Semicolon/SemicolonAfterInstructionFixerTest.php
index a5d8691c11e..8005be0ff4c 100644
--- a/tests/Fixer/Semicolon/SemicolonAfterInstructionFixerTest.php
+++ b/tests/Fixer/Semicolon/SemicolonAfterInstructionFixerTest.php
@@ -101,7 +101,7 @@ public function provideFixPre80Cases(): \Generator
 
     public function testOpenWithEcho(): void
     {
-        if (!ini_get('short_open_tag')) {
+        if (!\ini_get('short_open_tag')) {
             static::markTestSkipped('The short_open_tag option is required to be enabled.');
         }
 
diff --git a/tests/Tokenizer/TokensTest.php b/tests/Tokenizer/TokensTest.php
index 330a84440a8..6c9237ce006 100644
--- a/tests/Tokenizer/TokensTest.php
+++ b/tests/Tokenizer/TokensTest.php
@@ -375,8 +375,8 @@ public function provideMonolithicPhpDetectionCases(): iterable
         yield [false, 'Hello<?php echo "World!"; ?>'];
         yield [false, '<?php echo "Hello"; ?> World!'];
         // short open tag
-        yield [(bool) ini_get('short_open_tag'), "<?\n"];
-        yield [(bool) ini_get('short_open_tag'), "<?\n?>"];
+        yield [(bool) \ini_get('short_open_tag'), "<?\n"];
+        yield [(bool) \ini_get('short_open_tag'), "<?\n?>"];
         yield [false, " <?\n"];
         yield [false, "<?\n?> "];
         yield [false, "<?\n?><?\n"];