We've had code in OpenSSL written in C that was constant time until a newer version of both gcc and clang recognized (mask & a | ~mask & b) as a conditional ass

We've had code in OpenSSL written in C that was constant time until a newer version of both gcc and clang recognized (mask & a | ~mask & b) as a conditional assign and could do things like turn it into a branch. Edit: It can turn "b = foo(); c = (mask & a | ~mask & b)" into "if (mask) c = a; else c = foo();"