On 3/20/19 2:08 PM, Moritz Strübe wrote:
>
> Ok, I played around a bit. Interestingly, if I set
> -fsanitize=udefined and -fsanitize-undefined-trap-on-error the
> compiler detects that it will always trap, and optimizes the code
> accordingly (the code after the trap is removed).* Which kind of
> brings me to David's argument: Shouldn't the compiler warn if there
> is undefined behavior it certainly knows of?
Maybe an example would help.
Consider this code:
for (int i = start; i < limit; i++) {
foo(i * 5);
}
Should GCC be entitled to turn it into
int limit_tmp = i * 5;
for (int i = start * 5; i < limit_tmp; i += 5) {
foo(i);
}
If you answered "Yes, GCC should be allowed to do this", would you
want a warning? And how many such warnings might there be in a typical
program?
--
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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