I believe -Wcast-align should be made to warn on x86/64 as well, in the light of the above, as now it is the most dangerous territory, where you only get crashes if the compiler decides to vectorize code AND you get unaligned memory (the crash I got was VERY hard to reproduce). The problem I see is a conflict between the C standard (accesses must be aligned for int, etc.) and the x86/64 machine (accesses need not be aligned for int, etc.), and GCC optimizations using the former, while the warning flag (-Wcast-align) taking the latter. I would like more comments, ideas on this in general as well.
-Wcast-align depends on the STRICT_ALIGNMENT GCC macro being non-zero. The macro is set to zero for i386 which effectively disables the warning. I agree that it would be useful to enable -Wcast-align even for targets that tolerate unaligned accesses, not just for the reason you mention but also to help detect invalid alignment assumptions that may happen to be safe on the current target but not on others. To avoid breaking code that assumes the current behavior (e.g., expects -Wcast-align not to trigger on i386 with invalid alignment) the option could be extended to accept an optional argument. With the argument greater than 1 the option would trigger regardless of STRICT_ALIGNMENT. I would suggest to open a bug and reference this discussion. Martin
