Provided alternatives for some of the GCC bit-based intrinsics used by the...

Provided alternatives for some of the GCC bit-based intrinsics used by the scheduler. If the intrincics exist, they are used intead of the bitwise plain C implementations.


Former-commit-id: cda09e6bcc134010346b76faccaba39030179f41

src/intrinsics.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Coypright (c) 2015 Matthieu Schaller matthieu.schaller@durham.ac.uk)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_INTRINSICS_H
+#define SWIFT_INTRINSICS_H
+
+/**
+ * @brief Returns the number of leading 0-bits in x, starting at the most
+ * significant bit position. If x is 0, the result is undefined.
+ *
+ * This is a wrapper for the GCC intrinsics with an implementation (from
+ * Hacker's Delight) if the compiler intrisincs are not available.
+ */
+__attribute__((always_inline))
+    INLINE static int intrinsics_clz(unsigned int x) {
+
+#ifdef __GNUC__
+  /* Use GCC intrinsics if possible */
+  return __builtin_clz(x);
+#else
+  int n;
+
+  if (x == 0) return (32);
+  n = 0;
+  if (x <= 0x0000FFFF) {
+    n = n + 16;
+    x = x << 16;
+  }
+  if (x <= 0x00FFFFFF) {
+    n = n + 8;
+    x = x << 8;
+  }
+  if (x <= 0x0FFFFFFF) {
+    n = n + 4;
+    x = x << 4;
+  }
+  if (x <= 0x3FFFFFFF) {
+    n = n + 2;
+    x = x << 2;
+  }
+  if (x <= 0x7FFFFFFF) {
+    n = n + 1;
+  }
+  return n;
+#endif
+}
+
+/**
+ * @brief Returns the number of 1-bits in x.
+ *
+ * This is a wrapper for the GCC intrinsics with an implementation (from
+ * Hacker's Delight) if the compiler intrisincs are not available.
+ */
+__attribute__((always_inline))
+    INLINE static int intrinsics_popcount(unsigned int x) {
+
+#ifdef __GNUC__
+  /* Use GCC intrinsics if possible */
+  return __builtin_popcount(x);
+#else
+  x = (x & 0x55555555) + ((x >> 1) & 0x55555555);
+  x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
+  x = (x & 0x0F0F0F0F) + ((x >> 4) & 0x0F0F0F0F);
+  x = (x & 0x00FF00FF) + ((x >> 8) & 0x00FF00FF);
+  x = (x & 0x0000FFFF) + ((x >> 16) & 0x0000FFFF);
+  return x;
+#endif
+}
+
+#endif /* SWIFT_INTRINSICS_H */

src/scheduler.c

@@ -41,6 +41,7 @@
 #include "const.h"
 #include "cycle.h"
 #include "error.h"
+#include "intrinsics.h"
 #include "kernel.h"
 #include "timers.h"
 
@@ -813,8 +814,8 @@ void scheduler_reweight(struct scheduler *s) {
     else
       switch (t->type) {
         case task_type_sort:
-          t->weight += wscale * __builtin_popcount(t->flags) * t->ci->count *
-                       (sizeof(int) * 8 - __builtin_clz(t->ci->count));
+          t->weight += wscale * intrinsics_popcount(t->flags) * t->ci->count *
+                       (sizeof(int) * 8 - intrinsics_clz(t->ci->count));
           break;
         case task_type_self:
           t->weight += 1 * t->ci->count * t->ci->count;