use expanded variables for shell commands

Performance improvement for the shell commands in the Makefile.
By using expanded variables, the shell commands are only
evaluated once, instead of every time they are used.

closes https://github.com/official-stockfish/Stockfish/pull/4838

No functional change

diff --git a/src/Makefile b/src/Makefile
index 7b7ee41b6548b368358c9f54342dd05803b16b21..76ef6fdeb8d6865c5b6a99deed861e5872aa488e 100644 (file)
--- a/src/Makefile
+++ b/src/Makefile
@@ -20,9 +20,9 @@
 ### ==========================================================================
 
 ### Establish the operating system name
-KERNEL = $(shell uname -s)
+KERNEL := $(shell uname -s)
 ifeq ($(KERNEL),Linux)
-       OS = $(shell uname -o)
+       OS := $(shell uname -o)
 endif
 
 ### Target Windows OS
@@ -33,7 +33,7 @@ ifeq ($(OS),Windows_NT)
 else ifeq ($(COMP),mingw)
        target_windows = yes
        ifeq ($(WINE_PATH),)
-               WINE_PATH = $(shell which wine)
+               WINE_PATH := $(shell which wine)
        endif
 endif
 
@@ -116,7 +116,7 @@ ifeq ($(ARCH),)
 endif
 
 ifeq ($(ARCH), native)
-   override ARCH = $(shell $(SHELL) ../scripts/get_native_properties.sh | cut -d " " -f 1)
+   override ARCH := $(shell $(SHELL) ../scripts/get_native_properties.sh | cut -d " " -f 1)
 endif
 
 # explicitly check for the list of supported architectures (as listed with make help),
@@ -542,8 +542,8 @@ endif
 
 ### Sometimes gcc is really clang
 ifeq ($(COMP),gcc)
-       gccversion = $(shell $(CXX) --version 2>/dev/null)
-       gccisclang = $(findstring clang,$(gccversion))
+       gccversion := $(shell $(CXX) --version 2>/dev/null)
+       gccisclang := $(findstring clang,$(gccversion))
        ifneq ($(gccisclang),)
                profile_make = clang-profile-make
                profile_use = clang-profile-use
@@ -601,7 +601,7 @@ ifeq ($(optimize),yes)
        endif
 
        ifeq ($(comp),clang)
-               clangmajorversion = $(shell $(CXX) -dumpversion 2>/dev/null | cut -f1 -d.)
+               clangmajorversion := $(shell $(CXX) -dumpversion 2>/dev/null | cut -f1 -d.)
                ifeq ($(shell expr $(clangmajorversion) \< 16),1)
                        CXXFLAGS += -fexperimental-new-pass-manager
                endif
@@ -717,13 +717,13 @@ ifeq ($(pext),yes)
 endif
 
 ### 3.8.1 Try to include git commit sha for versioning
-GIT_SHA = $(shell git rev-parse HEAD 2>/dev/null | cut -c 1-8)
+GIT_SHA := $(shell git rev-parse HEAD 2>/dev/null | cut -c 1-8)
 ifneq ($(GIT_SHA), )
        CXXFLAGS += -DGIT_SHA=$(GIT_SHA)
 endif
 
 ### 3.8.2 Try to include git commit date for versioning
-GIT_DATE = $(shell git show -s --date=format:'%Y%m%d' --format=%cd HEAD 2>/dev/null)
+GIT_DATE := $(shell git show -s --date=format:'%Y%m%d' --format=%cd HEAD 2>/dev/null)
 ifneq ($(GIT_DATE), )
        CXXFLAGS += -DGIT_DATE=$(GIT_DATE)
 endif