Add AVX2-accelerated UTF-16 decoding/encoding routines

As with other SIMD-accelerated functions in php-src, the new UTF-16
encoding and decoding routines can be compiled either with AVX2
acceleration "always on", "always off", or else with runtime detection
of AVX2 support.

With the new UTF-16 decoder/encoder, conversion of extremely short
strings (as in several bytes) has the same performance as before,
and conversion of medium-length (~100 character) strings is about 65%
faster, but conversion of long (~10,000 character) strings is around
6 times faster.

Many other mbstring functions will also be faster now when handling
UTF-16; for example, mb_strlen is almost 3 times faster on medium
strings, and almost 9 times faster on long strings. (Why does mb_strlen
benefit more from AVX2 acceleration than mb_convert_encoding? It's
because mb_strlen only needs to decode, but not re-encode, the input
string, and the UTF-16 decoder benefits much more from SIMD
acceleration than the UTF-16 encoder.)

Author: alexdowad

Zend/zend_bitset.h

@@ -19,6 +19,13 @@
 #ifndef _ZEND_BITSET_H_
 #define _ZEND_BITSET_H_
 
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include "zend_portability.h"
+#include "zend_long.h"
+
 typedef zend_ulong *zend_bitset;
 
 #define ZEND_BITSET_ELM_SIZE sizeof(zend_ulong)

build/php.m4

@@ -2643,6 +2643,27 @@ AC_DEFUN([PHP_CHECK_BUILTIN_SADDLL_OVERFLOW], [
    [$have_builtin_saddll_overflow], [Whether the compiler supports __builtin_saddll_overflow])
 ])
 
+dnl
+dnl PHP_CHECK_BUILTIN_USUB_OVERFLOW
+dnl
+AC_DEFUN([PHP_CHECK_BUILTIN_USUB_OVERFLOW], [
+  AC_MSG_CHECKING([for __builtin_usub_overflow])
+
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([], [[
+    unsigned int tmpvar;
+    return __builtin_usub_overflow(3, 7, &tmpvar);
+  ]])], [
+    have_builtin_usub_overflow=1
+    AC_MSG_RESULT([yes])
+  ], [
+    have_builtin_usub_overflow=0
+    AC_MSG_RESULT([no])
+  ])
+
+  AC_DEFINE_UNQUOTED([PHP_HAVE_BUILTIN_USUB_OVERFLOW],
+   [$have_builtin_usub_overflow], [Whether the compiler supports __builtin_usub_overflow])
+])
+
 dnl
 dnl PHP_CHECK_BUILTIN_SSUBL_OVERFLOW
 dnl

configure.ac

@@ -504,6 +504,8 @@ dnl Check __builtin_saddl_overflow
 PHP_CHECK_BUILTIN_SADDL_OVERFLOW
 dnl Check __builtin_saddll_overflow
 PHP_CHECK_BUILTIN_SADDLL_OVERFLOW
+dnl Check __builtin_usub_overflow
+PHP_CHECK_BUILTIN_USUB_OVERFLOW
 dnl Check __builtin_ssubl_overflow
 PHP_CHECK_BUILTIN_SSUBL_OVERFLOW
 dnl Check __builtin_ssubll_overflow