build: Use __builtin_popcount() if available.

configure.ac

@@ -88,6 +88,7 @@ AS_IF([test "x$with_spirv_tools" = "xyes"],
 PKG_CHECK_MODULES([XCB], [xcb xcb-keysyms])
 
 dnl Check for functions
+VKD3D_CHECK_BUILTIN_POPCOUNT
 VKD3D_CHECK_SYNC_ADD_AND_FETCH_FUNC
 VKD3D_CHECK_SYNC_SUB_AND_FETCH_FUNC
 

include/private/vkd3d_common.h

@@ -39,9 +39,13 @@ static inline size_t align(size_t addr, size_t alignment)
 
 static inline unsigned int vkd3d_popcount(unsigned int v)
 {
+#ifdef HAVE_BUILTIN_POPCOUNT
+    return __builtin_popcount(v);
+#else
     v -= (v >> 1) & 0x55555555;
     v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
     return (((v + (v >> 4)) & 0x0f0f0f0f) * 0x01010101) >> 24;
+#endif
 }
 
 #ifndef _WIN32

m4/check-builtin-functions.m4

@@ -17,3 +17,13 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([int main(void) { return __sync_sub_and_fetch((in
                          [1],
                          [Define to 1 if you have __sync_sub_and_fetch.])],
                [AC_MSG_RESULT([no])])])
+
+dnl VKD3D_CHECK_BUILTIN_POPCOUNT
+AC_DEFUN([VKD3D_CHECK_BUILTIN_POPCOUNT],
+[AC_MSG_CHECKING([for __builtin_popcount])
+AC_LINK_IFELSE([AC_LANG_SOURCE([int main(void) { return __builtin_popcount(0); }])],
+               [AC_MSG_RESULT([yes])
+               AC_DEFINE([HAVE_BUILTIN_POPCOUNT],
+                         [1],
+                         [Define to 1 if you have __builtin_popcount.])],
+               [AC_MSG_RESULT([no])])])