Workaround for VC++ 2015 Update 2 code-gen bug

third_party/libxml/src/xmlstring.c

 /*
  * string.c : an XML string utilities module
  *
  * This module provides various utility functions for manipulating
  * the xmlChar* type. All functions named xmlStr* have been moved here
  * from the parser.c file (their original home).
  *
  * See Copyright for the status of this software.
  *
  * UTF8 string routines from:
@@ skipping 803 matching lines @@
  * @utf:  a sequence of UTF-8 encoded bytes
  * @len:  the number of characters in the array
  *
  * storage size of an UTF8 string
  * the behaviour is not garanteed if the input string is not UTF-8
  *
  * Returns the storage size of
  * the first 'len' characters of ARRAY
  */
 
+#if _MSC_FULL_VER && _MSC_FULL_VER == 190023918
+// Workaround for a /O1 ("s") optimization bug in VS 2015 Update 2, remove once
+// the fix is released. crbug.com/599427
+// https://connect.microsoft.com/VisualStudio/feedback/details/2582138
+#pragma optimize("t", on)
+#endif
+
 int
 xmlUTF8Strsize(const xmlChar *utf, int len) {
     const xmlChar   *ptr=utf;
     xmlChar         ch;
 
     if (utf == NULL)
         return(0);
 
     if (len <= 0)
         return(0);
 
     while ( len-- > 0) {
         if ( !*ptr )
             break;
         if ( (ch = *ptr++) & 0x80)
             while ((ch<<=1) & 0x80 ) {
                 ptr++;
                 if (*ptr == 0) break;
             }
     }
     return (ptr - utf);
 }
 
+#if _MSC_FULL_VER && _MSC_FULL_VER == 190023918
+// Restore the original optimization settings.
+#pragma optimize("", on)
+#endif
 
 /**
  * xmlUTF8Strndup:
  * @utf:  the input UTF8 *
  * @len:  the len of @utf (in chars)
  *
  * a strndup for array of UTF8's
  *
  * Returns a new UTF8 * or NULL
  */
@@ skipping 118 matching lines @@
                 if ( (*utf++ & 0xc0) != 0x80 )
                     return(NULL);
         }
     }
 
     return(xmlUTF8Strndup(utf, len));
 }
 
 #define bottom_xmlstring
 #include "elfgcchack.h"