Enable popcount and prefetch for ppc-64

PowerPC has had popcount instructions for a long time, at least as far
back as POWER5 (released 2004). Enable them via a gcc builtin.

Using a gcc builtin has the added bonus that if compiled for a processor
that lacks a hardware instruction, gcc will include a software popcount
implementation that does not use the instruction. It might be slower
than the table lookups (or it might be faster) but it will certainly work.
So this isn't going to break anything.

On my POWER8 VM, this leads to a ~4.27% speedup.

Fir prefetch, the gcc builtin generates a 'dcbt' instruction, which is
supported at least as far back as the G5 (2002) and POWER4 (2001).

This leads to a ~5% speedup on my POWER8 VM.

No functional change

diff --git a/src/Makefile b/src/Makefile
index 2d6042e20226acd4cbf5bbef9a008e080c6957f3..285d314ec302d34e9d200bce53fa5c42ad243fdf 100644 (file)
--- a/src/Makefile
+++ b/src/Makefile
@@ -136,6 +136,8 @@ endif
 ifeq ($(ARCH),ppc-64)
        arch = ppc64
        bits = 64
+       popcnt = yes
+       prefetch = yes
 endif
 
 
@@ -313,7 +315,9 @@ endif
 
 ### 3.6 popcnt
 ifeq ($(popcnt),yes)
-       ifeq ($(comp),icc)
+       ifeq ($(arch),ppc64)
+               CXXFLAGS += -DUSE_POPCNT
+       else ifeq ($(comp),icc)
                CXXFLAGS += -msse3 -DUSE_POPCNT
        else
                CXXFLAGS += -msse3 -mpopcnt -DUSE_POPCNT