Increase optimization level of Clang

Set optimization level to 4 and get a 2.564% faster binary:

Stockfish (Clang, Level 4) bench:
$ make build ARCH=osx-x86-64 COMP=clang
(Clang does not support PGO)
Average of 4 trials:
Total time (ms): 5137.5
Nodes searched: 5631135
Nodes/second: 1096084.5

Stockfish (Clang, Level 3) bench:
$ make build ARCH=osx-x86-64 COMP=clang
(Clang does not support PGO)
Average of 4 trials:
Total time (ms): 5269.25
Nodes searched: 5631135
Nodes/second: 1068679.25

Stockfish (GCC, PGO) bench:
$ make profile-build ARCH=osx-x86-64
Average of 4 trials:
Total time (ms): 5286
Nodes searched: 5631135
Nodes/second: 1065292.25

Suggestion and performance tests by Daylen Yang.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/Makefile b/src/Makefile
index 71aa7b30d195370738bcab3705f4385b7328b308..782971e938c1364494642aa17112f8c3fda1319c 100644 (file)
--- a/src/Makefile
+++ b/src/Makefile
@@ -270,7 +270,7 @@ ifeq ($(optimize),yes)
        endif
 
        ifeq ($(comp),clang)
-               CXXFLAGS += -O3
+               CXXFLAGS += -O4
 
                ifeq ($(os),osx)
                        ifeq ($(arch),i386)