ext/standard: Return the input of htmlspecialchars() when nothing needs encoding

htmlspecialchars() allocated a buffer of twice the input and decoded it
character by character, even when the result was the input itself.

The input is now scanned first for the characters that need encoding and
for invalid multi-byte sequences, with SSE2 on 16-byte blocks. When there
is none, the input string is returned, as html_entity_decode() and
htmlspecialchars_decode() already do since 68dc754. Otherwise, encoding
starts after the part that was scanned.

The @refcount 1 annotations of htmlspecialchars() and htmlentities() are
removed since they can now return their argument.

Author: nicolas-grekas

NEWS

@@ -125,6 +125,8 @@ PHP                                                                        NEWS
     in a php://filter URL. (Sjoerd Langkemper)
   . Improved performance of array_chunk() when not preserving keys.
     (mehmetcansahin)
+  . Improved performance of htmlspecialchars() when nothing needs encoding.
+    (Nicolas Grekas)
 
 - URI:
   . Fix casing of enum cases in UriHostType and UrlHostType to match the RFC

UPGRADING

@@ -105,6 +105,8 @@ PHP 8.7 UPGRADE NOTES
   . Improved performance of str_rot13().
   . Improved performance of pack() for large strings using the a, A and Z
     formats.
+  . htmlspecialchars() returns its input without copying it when nothing needs
+    encoding.
 
 - MBString:
   . Improved performance of mb_strlen for UTF-8 strings.

Zend/Optimizer/zend_func_infos.h

@@ -463,8 +463,6 @@ static const func_info_t func_infos[] = {
 	F1("inet_pton", MAY_BE_STRING|MAY_BE_FALSE),
 	F1("metaphone", MAY_BE_STRING),
 	F1("headers_list", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
-	F1("htmlspecialchars", MAY_BE_STRING),
-	F1("htmlentities", MAY_BE_STRING),
 	F1("get_html_translation_table", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_STRING),
 	F1("bin2hex", MAY_BE_STRING),
 	F1("hex2bin", MAY_BE_STRING|MAY_BE_FALSE),

ext/standard/basic_functions.stub.php

@@ -2273,14 +2273,12 @@ function headers_list(): array {}
 
 /* {{{ html.c */
 
-/** @refcount 1 */
 function htmlspecialchars(string $string, int $flags = ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401, ?string $encoding = null, bool $double_encode = true): string {}
 
 function htmlspecialchars_decode(string $string, int $flags = ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401): string {}
 
 function html_entity_decode(string $string, int $flags = ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401, ?string $encoding = null): string {}
 
-/** @refcount 1 */
 function htmlentities(string $string, int $flags = ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401, ?string $encoding = null, bool $double_encode = true): string {}
 
 /**