Remove architecture specific sched_cpucount optimizations

And replace the generic algorithm with the Brian Kernighan's one.
GCC optimize it with popcnt if the architecture supports, so there
is no need to add the extra POPCNT define to enable it.

This is really a micro-optimization that only adds complexity:
recent ABIs already support it (x86-64-v2 or power64le) and it
simplifies the code for internal usage, since i686 does not allow an
internal iFUNC call.

Checked on x86_64-linux-gnu, aarch64-linux-gnu, and
powerpc64le-linux-gnu.

1 files changed, 14 insertions, 26 deletions

diff --git a/posix/sched_cpucount.c b/posix/sched_cpucount.c
index b0ca4ea7bc..63d0e99590 100644
--- a/posix/sched_cpucount.c
+++ b/posix/sched_cpucount.c
@@ -17,36 +17,24 @@
 
 #include <sched.h>
 
+/* Counting bits set, Brian Kernighan's way.
+   Using a open-coded routine is slight better for architectures that
+   do not have a popcount instruction (compiler might emit a library
+   call).  */
+static inline int
+countbits (__cpu_mask v)
+{
+  int s = 0;
+  for (; v != 0; s++)
+    v &= v - 1;
+  return s;
+}
 
 int
 __sched_cpucount (size_t setsize, const cpu_set_t *setp)
 {
   int s = 0;
-  const __cpu_mask *p = setp->__bits;
-  const __cpu_mask *end = &setp->__bits[setsize / sizeof (__cpu_mask)];
-
-  while (p < end)
-    {
-      __cpu_mask l = *p++;
-
-#ifdef POPCNT
-      s += POPCNT (l);
-#else
-      if (l == 0)
-	continue;
-
-      _Static_assert (sizeof (l) == sizeof (unsigned int)
-		      || sizeof (l) == sizeof (unsigned long)
-		      || sizeof (l) == sizeof (unsigned long long),
-		      "sizeof (__cpu_mask");
-      if (sizeof (__cpu_mask) == sizeof (unsigned int))
-	s += __builtin_popcount (l);
-      else if (sizeof (__cpu_mask) == sizeof (unsigned long))
-	s += __builtin_popcountl (l);
-      else
-	s += __builtin_popcountll (l);
-#endif
-    }
-
+  for (int i = 0; i < setsize / sizeof (__cpu_mask); i++)
+    s += countbits (setp->__bits[i]);
   return s;
 }