host-utils: Use __int128_t for mul[us]64

Replace some x86_64 specific inline assembly with something that
all 64-bit hosts ought to optimize well.  At worst this becomes
a call to the gcc __multi3 routine, which is no worse than our
implementation in util/host-utils.c.

With gcc 4.7, we get identical code generation for x86_64.  We
now get native multiplication on ia64 and s390x hosts.  With minor
improvements to gcc we can get it for ppc64 as well.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/configure b/configure
index 8789324..bf5970f 100755
--- a/configure
+++ b/configure
@@ -3150,6 +3150,22 @@ if compile_prog "" "" ; then
     cpuid_h=yes
 fi
 
+########################################
+# check if __[u]int128_t is usable.
+
+int128=no
+cat > $TMPC << EOF
+__int128_t a;
+__uint128_t b;
+int main (void) {
+  a = a + b;
+  b = a * b;
+  return 0;
+}
+EOF
+if compile_prog "" "" ; then
+    int128=yes
+fi
 
 ##########################################
 # End of CC checks
@@ -3692,6 +3708,10 @@ if test "$cpuid_h" = "yes" ; then
   echo "CONFIG_CPUID_H=y" >> $config_host_mak
 fi
 
+if test "$int128" = "yes" ; then
+  echo "CONFIG_INT128=y" >> $config_host_mak
+fi
+
 if test "$glusterfs" = "yes" ; then
   echo "CONFIG_GLUSTERFS=y" >> $config_host_mak
 fi