Add -fno-var-tracking-assignments to pysairedis_wrap.cpp when built with GCC

This improves compilation time by a total of 16m by disabling the GCC
feature "Variable Tracking Assingments."

The trade-off for disabling this feature is reduced debuggability if anyone
needs to go through the object file pysairedis_wrap.o with a debugger. Please
see the background below for details.

This was identified via the following issue in the SWIG project:
- swig/swig#2384 (comment)

This is a performance issue in GCC specifically, not CLANG.

Results:
On a server with the following specifications, the build time for
libsairedis went from 20m23s down to 3m50s.

    CPU: Intel(R) Xeon(R) Gold 6430
    RAM: 1Tb DDR5
    OS: Ubuntu 22.04
    g++: g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0

On an Apple MacBook Pro (with a Debian build VM), the build time
for libsairedis also dropped significantly from 17m43s down to
3m46s

    CPU: Apple M3 Pro
    RAM: 18Gb
    OS: Debian 12 Bookworm
    g++: g++ (Debian 12.2.0-14) 12.2.0

Background:
- https://gcc.gnu.org/wiki/Var_Tracking_Assignments
- https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/6/html/developer_guide/ch-debug-vta#ch-debug-vta

Signed-off-by: Mike RE Mallin <[email protected]>

Author: mikemallin

configure.ac

@@ -278,6 +278,8 @@ AC_DEFINE([SAI_GIT_REVISION],
         "[m4_esyscmd([echo -n $(cd SAI && git rev-parse --short HEAD || echo 0000000)])]",
         [SAI git revision information])
 
+AM_CONDITIONAL(CXX_IS_GCC, test x$CXX = xg++)
+
 AC_OUTPUT(Makefile
           meta/Makefile
           lib/Makefile

pyext/py2/Makefile.am

@@ -4,11 +4,27 @@ SOURCES=../pysairedis.h ../pysairedis.cpp
 pkgpython_PYTHON = pysairedis.py __init__.py
 pkgpyexec_LTLIBRARIES = _pysairedis.la
 
+#
+# -fno-var-tracking-assignments is set for the GCC compiler
+# suite to improve build performance. pysairedis_wrap.cpp is
+# automatically generated by SWIG, so it's not a big loss.
+#
+if CXX_IS_GCC
+CXXFLAGS_COMPILER = "-fno-var-tracking-assignments"
+else
+CXXFLAGS_COMPILER = ""
+endif
+
 AM_CXXFLAGS = $(SAIINC) -I$(top_srcdir)/lib -I..
 
 BUILT_SOURCES = pysairedis_wrap.cpp
 
-_pysairedis_la_SOURCES = pysairedis_wrap.cpp $(SOURCES)
+libpysairedis_wrap_la_SOURCES = pysairedis_wrap.cpp
+libpysairedis_wrap_la_CXXFLAGS = $(PYTHON2_CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS_COMMON) \
+						  -Wno-cast-qual -Wno-shadow -Wno-redundant-decls -Wno-conversion $(CXXFLAGS_COMPILER) $(NO_CAST_FUNCTION_TYPE)
+
+noinst_LTLIBRARIES = libpysairedis_wrap.la
+_pysairedis_la_SOURCES = $(SOURCES)
 _pysairedis_la_CXXFLAGS = $(PYTHON2_CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS_COMMON) \
 						  -Wno-cast-qual -Wno-shadow -Wno-redundant-decls -Wno-conversion $(NO_CAST_FUNCTION_TYPE)
 
@@ -18,7 +34,7 @@ _pysairedis_la_LDFLAGS = -module \
 		-L$(top_srcdir)/meta/.libs -lsaimetadata -lsaimeta \
 		-lzmq
 
-_pysairedis_la_LIBADD = $(PYTHON2_LIBS)
+_pysairedis_la_LIBADD = $(PYTHON2_LIBS) libpysairedis_wrap.la
 
 SWIG_FLAG = -Wall -c++ -python -keyword
 if ARCH64

pyext/py3/Makefile.am

@@ -4,11 +4,28 @@ SOURCES=../pysairedis.h ../pysairedis.cpp
 pkgpython3_PYTHON = pysairedis.py __init__.py
 pkgpy3exec_LTLIBRARIES = _pysairedis.la
 
+#
+# -fno-var-tracking-assignments is set for the GCC compiler
+# suite to improve build performance. pysairedis_wrap.cpp is
+# automatically generated by SWIG, so it's not a big loss.
+#
+if CXX_IS_GCC
+CXXFLAGS_COMPILER = "-fno-var-tracking-assignments"
+else
+CXXFLAGS_COMPILER = ""
+endif
+
 AM_CXXFLAGS = $(SAIINC) -I$(top_srcdir)/lib -I..
 
 BUILT_SOURCES = pysairedis_wrap.cpp
 
-_pysairedis_la_SOURCES = pysairedis_wrap.cpp $(SOURCES)
+
+libpysairedis_wrap_la_SOURCES = pysairedis_wrap.cpp
+libpysairedis_wrap_la_CXXFLAGS = $(PYTHON3_CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS_COMMON) \
+						  -Wno-cast-qual -Wno-shadow -Wno-redundant-decls -Wno-conversion $(CXXFLAGS_COMPILER) $(NO_CAST_FUNCTION_TYPE)
+
+noinst_LTLIBRARIES = libpysairedis_wrap.la
+_pysairedis_la_SOURCES = $(SOURCES)
 _pysairedis_la_CXXFLAGS = $(PYTHON3_CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS_COMMON) \
 						  -Wno-cast-qual -Wno-shadow -Wno-redundant-decls -Wno-conversion $(NO_CAST_FUNCTION_TYPE)
 
@@ -18,7 +35,7 @@ _pysairedis_la_LDFLAGS = -module \
 		-L$(top_srcdir)/meta/.libs -lsaimetadata -lsaimeta \
 		-lzmq
 
-_pysairedis_la_LIBADD = $(PYTHON3_BLDLIBRARY)
+_pysairedis_la_LIBADD = $(PYTHON3_BLDLIBRARY) libpysairedis_wrap.la
 
 SWIG_FLAG = -Wall -c++ -python -keyword
 if ARCH64