From: Daniel Axtens <dja@axtens.net>
Date: Wed, 10 Jul 2019 23:12:54 +0000 (+1000)
Subject: Enable popcount and prefetch for ppc-64
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=fa1a2a0667ff81f04e94cab078c50c2d51f4cb5e;hp=ca51d1ee63f376e0eb6efb6f3d5d901e4b2a5bb0

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 2d6042e2..285d314e 100644
--- 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