From: Joost VandeVondele <Joost.VandeVondele@gmail.com>
Date: Thu, 12 Sep 2019 19:25:58 +0000 (+0200)
Subject: Add sse4 if bmi2 is enabled
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=db00e1625eb46517f61085ffd3bcd28779e71220;ds=inline

Add sse4 if bmi2 is enabled

The only change done to the Makefile to get a somewhat faster binary as
discussed in #2291 is to add -msse4 to the compile options of the bmi2 build.
Since all processors supporting bmi2 also support sse4 this can be done easily.
It is a useful step to avoid sending around custom and poorly tested builds.

The speedup isn't enough to pass [0,4] but it is roughly 1.15Elo and a LOS of 90%:
LLR: -2.95 (-2.94,2.94) [0.00,4.00]
Total: 93009 W: 20519 L: 20316 D: 52174

Also rewrite the documentation for the user when using `make --help`, so that
the order of architectures for x86-64 has the more performant build one on top.

Closes https://github.com/official-stockfish/Stockfish/pull/2300

No functional change
---

diff --git a/src/Makefile b/src/Makefile
index 285d314e..6deb0e27 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -328,7 +328,7 @@ endif
 ifeq ($(pext),yes)
 	CXXFLAGS += -DUSE_PEXT
 	ifeq ($(comp),$(filter $(comp),gcc clang mingw))
-		CXXFLAGS += -mbmi2
+		CXXFLAGS += -msse4 -mbmi2
 	endif
 endif
 
@@ -379,9 +379,9 @@ help:
 	@echo ""
 	@echo "Supported archs:"
 	@echo ""
-	@echo "x86-64                  > x86 64-bit"
-	@echo "x86-64-modern           > x86 64-bit with popcnt support"
-	@echo "x86-64-bmi2             > x86 64-bit with pext support"
+	@echo "x86-64-bmi2             > x86 64-bit with pext support (also enables SSE4)"
+	@echo "x86-64-modern           > x86 64-bit with popcnt support (also enables SSE3)"
+	@echo "x86-64                  > x86 64-bit generic"
 	@echo "x86-32                  > x86 32-bit with SSE support"
 	@echo "x86-32-old              > x86 32-bit fall back for old hardware"
 	@echo "ppc-64                  > PPC 64-bit"