diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9e1c527..eee5131 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -12,6 +12,6 @@ build-centos:
       - source /opt/rh/devtoolset-7/enable
       - mkdir build
       - cd build
-      - cmake3 ..
+      - CC=/usr/bin/clang CXX=/usr/bin/clang++ cmake3 ..
       - make -j2
       - make test
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 190074c..e58182f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,7 +10,7 @@ else()
   message(WARNING "compiler ${CMAKE_CXX_COMPILER_ID} officially not supported")
 endif()
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++17 -Wpedantic -Ofast -march=native -faligned-new -funroll-loops -fopenmp")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++17 -Wpedantic -O2 -march=native -faligned-new -funroll-loops -fopenmp")
 #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++14 -g -Wpedantic -Ofast -march=native -faligned-new -funroll-loops -fopenmp -ftemplate-backtrace-limit=0")
 #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++14 -g -Wpedantic -O0 -march=native -faligned-new -funroll-loops -fopenmp")
 
diff --git a/src/include/base/assert.h b/src/include/base/assert.h
index d0a5c63..d429a76 100644
--- a/src/include/base/assert.h
+++ b/src/include/base/assert.h
@@ -5,9 +5,8 @@
 #define CXZ_ERRTAG __FILE__ << '@' << __LINE__ << '(' << __func__ << "): error"
 #define CXZ_WARNTAG __FILE__ << '@' << __LINE__ << ": warning"
 #define CXZ_ERROR(errmsg) {\
-    std::stringstream ss;\
-    ss << CXZ_ERRTAG << ": " << errmsg << std::flush;\
-    throw std::runtime_error(ss.str()); }
+    auto mkerr = [&](){ std::stringstream ss; ss << CXZ_ERRTAG << ": " << errmsg << std::flush; return ss.str(); }; \
+    throw std::runtime_error(mkerr()); }
 
 #define CXZ_WARNING(errmsg) {\
     std::cerr << CXZ_WARNTAG << ": " << errmsg << std::endl; }