Use -Wshift-count-negative flag to warn bit shifting of a negative amount. #include <stdio.h> int main() { int x = 8; int y = x << -1; printf("%d\n", y); return 0; } The result of arithmetics is undefined if we perform bit shifting by a negative amount, which may lead to unexpected behavior. $ # M1 Mac (Monterey) + Apple clang 13.1.6 $ clang sample.cpp -o sample -Wshift-count-negative sample.

Use -Wsign-conversion flag for clang to warn implicit sign conversion. int main() { unsigned int x = -1; return 0; } $ # M1 Mac (Ventura) + Apple clang 14.0.0 $ clang sample.cpp -Wsign-conversion sample.cpp:3:22: warning: implicit conversion changes signedness: 'int' to 'unsigned int' [-Wsign-conversion] unsigned int x = -1; ~ ^~ 1 warning generated. Suppress warnings Use -Wno-sign-conversion to suppress warnings. It can be used to cancel -Wsign-conversion if already set.

Use -Wmacro-redefined flag to warn redefined macros by clang. #define MY_DEFINE 111 #define MY_DEFINE 222 int main(void) { return 0; } $ # M1 Mac (Ventura) + Apple clang 14.0.0 $ clang sample.cpp -Wmacro-redefined sample.cpp:2:9: warning: 'MY_DEFINE' macro redefined [-Wmacro-redefined] #define MY_DEFINE 222 ^ sample.cpp:1:9: note: previous definition is here #define MY_DEFINE 111 ^ 1 warning generated. The warnings are displayed automatically: clang enables -Wmacro-redefined by default.