gcc and clang have been getting better at this recently. For instance if you do an "x == x" comparison for an int x clang will warn "warning: self-comparison always evaluates to true [-Wtautological-compare]".

I completely agree that having these warnings in the compiler is much better than a standalone analysis tool, because they're less likely to be ignored. But I think it may have been a bit of a shift of mindset for the compiler developers to put more effort into warnings and diagnosing dubious code rather than simply being a code generator for correct code.