[gcc r12-49] Revert "Use std::thread::hardware_concurrency in lto-wrapper.c."

[gcc r12-49] Revert "Use std::thread::hardware_concurrency in lto-wrapper.c."

[Martin Liska]

https://gcc.gnu.org/g:f2b4f212a97ae137c2a8ecafe7ed2cb5b5016b6b

commit r12-49-gf2b4f212a97ae137c2a8ecafe7ed2cb5b5016b6b
Author: Martin Liska <mliska@suse.cz>
Date:   Wed Apr 21 21:33:41 2021 +0200

    Revert "Use std::thread::hardware_concurrency in lto-wrapper.c."
    
    This reverts commit 0a18305ee11e139838771f96c5a037a29606236e.

Diff:
---
 gcc/lto-wrapper.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 108 insertions(+), 5 deletions(-)

diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
index 6ba401007f6..0b626d7c811 100644
--- a/gcc/lto-wrapper.c
+++ b/gcc/lto-wrapper.c
@@ -49,8 +49,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "lto-section-names.h"
 #include "collect-utils.h"
 
-#include <thread>
-
 /* Environment variable, used for passing the names of offload targets from GCC
    driver to lto-wrapper.  */
 #define OFFLOAD_TARGET_NAMES_ENV	"OFFLOAD_TARGET_NAMES"
@@ -1201,6 +1199,113 @@ cmp_priority (const void *a, const void *b)
   return *((const int *)b)-*((const int *)a);
 }
 
+/* Number of CPUs that can be used for parallel LTRANS phase.  */
+
+static unsigned long nthreads_var = 0;
+
+#ifdef HAVE_PTHREAD_AFFINITY_NP
+unsigned long cpuset_size;
+static unsigned long get_cpuset_size;
+cpu_set_t *cpusetp;
+
+unsigned long
+static cpuset_popcount (unsigned long cpusetsize, cpu_set_t *cpusetp)
+{
+#ifdef CPU_COUNT_S
+  /* glibc 2.7 and above provide a macro for this.  */
+  return CPU_COUNT_S (cpusetsize, cpusetp);
+#else
+#ifdef CPU_COUNT
+  if (cpusetsize == sizeof (cpu_set_t))
+    /* glibc 2.6 and above provide a macro for this.  */
+    return CPU_COUNT (cpusetp);
+#endif
+  size_t i;
+  unsigned long ret = 0;
+  STATIC_ASSERT (sizeof (cpusetp->__bits[0]) == sizeof (unsigned long int));
+  for (i = 0; i < cpusetsize / sizeof (cpusetp->__bits[0]); i++)
+    {
+      unsigned long int mask = cpusetp->__bits[i];
+      if (mask == 0)
+	continue;
+      ret += __builtin_popcountl (mask);
+    }
+  return ret;
+#endif
+}
+#endif
+
+/* At startup, determine the default number of threads.  It would seem
+   this should be related to the number of cpus online.  */
+
+static void
+init_num_threads (void)
+{
+#ifdef HAVE_PTHREAD_AFFINITY_NP
+#if defined (_SC_NPROCESSORS_CONF) && defined (CPU_ALLOC_SIZE)
+  cpuset_size = sysconf (_SC_NPROCESSORS_CONF);
+  cpuset_size = CPU_ALLOC_SIZE (cpuset_size);
+#else
+  cpuset_size = sizeof (cpu_set_t);
+#endif
+
+  cpusetp = (cpu_set_t *) xmalloc (gomp_cpuset_size);
+  do
+    {
+      int ret = pthread_getaffinity_np (pthread_self (), gomp_cpuset_size,
+					cpusetp);
+      if (ret == 0)
+	{
+	  /* Count only the CPUs this process can use.  */
+	  nthreads_var = cpuset_popcount (cpuset_size, cpusetp);
+	  if (nthreads_var == 0)
+	    break;
+	  get_cpuset_size = cpuset_size;
+#ifdef CPU_ALLOC_SIZE
+	  unsigned long i;
+	  for (i = cpuset_size * 8; i; i--)
+	    if (CPU_ISSET_S (i - 1, cpuset_size, cpusetp))
+	      break;
+	  cpuset_size = CPU_ALLOC_SIZE (i);
+#endif
+	  return;
+	}
+      if (ret != EINVAL)
+	break;
+#ifdef CPU_ALLOC_SIZE
+      if (cpuset_size < sizeof (cpu_set_t))
+	cpuset_size = sizeof (cpu_set_t);
+      else
+	cpuset_size = cpuset_size * 2;
+      if (cpuset_size < 8 * sizeof (cpu_set_t))
+	cpusetp
+	  = (cpu_set_t *) realloc (cpusetp, cpuset_size);
+      else
+	{
+	  /* Avoid fatal if too large memory allocation would be
+	     requested, e.g. kernel returning EINVAL all the time.  */
+	  void *p = realloc (cpusetp, cpuset_size);
+	  if (p == NULL)
+	    break;
+	  cpusetp = (cpu_set_t *) p;
+	}
+#else
+      break;
+#endif
+    }
+  while (1);
+  cpuset_size = 0;
+  nthreads_var = 1;
+  free (cpusetp);
+  cpusetp = NULL;
+#endif
+#ifdef _SC_NPROCESSORS_ONLN
+  nthreads_var = sysconf (_SC_NPROCESSORS_ONLN);
+#endif
+}
+
+/* FIXME: once using -std=c++11, we can use std::thread::hardware_concurrency.  */
+
 /* Test and return reason why a jobserver cannot be detected.  */
 
 static const char *
@@ -1284,9 +1389,6 @@ run_gcc (unsigned argc, char *argv[])
   const char *incoming_dumppfx = dumppfx = NULL;
   static char current_dir[] = { '.', DIR_SEPARATOR, '\0' };
 
-  /* Number of CPUs that can be used for parallel LTRANS phase.  */
-  unsigned long nthreads_var = std::thread::hardware_concurrency ();
-
   /* Get the driver and options.  */
   collect_gcc = getenv ("COLLECT_GCC");
   if (!collect_gcc)
@@ -1678,6 +1780,7 @@ cont1:
       else if (auto_parallel)
 	{
 	  char buf[256];
+	  init_num_threads ();
 	  if (nthreads_var == 0)
 	    nthreads_var = 1;
 	  if (verbose)