在 2018/11/24 5:36, Marc Glisse 写道: > On Fri, 23 Nov 2018, Helmut Eller wrote: > >> On Fri, Nov 23 2018, Marc Glisse wrote: >> >>> On Fri, 23 Nov 2018, Helmut Eller wrote: >>> >>>> when compiling this example with gcc -O2 -ftrapv: >>>> [...] >>> Try with "-fsanitize=undefined >>> -fsanitize-undefined-trap-on-error". -ftrapv is quite broken and not >>> really maintained. I think fixing it would mean making it an alias for >>> the sanitizer version. >> >> Thanks for the quick reply. That does indeed produce exactly the code I >> want. >> >> It doesn't seem so detect overflow for short or char types, though: > > That's because there is no overflow. Read about integer promotion. I think I had better say something about this. You are right; there is no overflow. But who needs such apparently deficient (if not incomplete at all) behavior? People could start arguing that integer promotion is mandated by the C standard and is what 'portable' code might rely on. Yes you are right, totally right about a _very_ poor excuse: The so-called 'portable' code should not rely on the `int` -> `short` conversion either, which is implementation-defined and not so portable after all. It is a shame for C to have integer promotion. It is a flaw for UBSan to discriminate overflows on `short`. -- Best regards, LH_Mouse
