[Bug rtl-optimization/82677] Many projects (linux, coreutils, GMP, gcrypt, openSSL, etc) are misusing asm(divq/divl) etc, potentially resulting in faulty/unintended optimisations

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82677

--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 23 Oct 2017, infinity0 at pwned dot gg wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82677
> 
> --- Comment #6 from infinity0 at pwned dot gg ---
> What I mean is, even if you do change GCC to fix the unintended optimisation,
> other projects' code are *still wrong* - it's only correct if you can assume
> the C compiler is optimising your code in a very specific way, that happens to
> safe for the specific sorts of "side effects" that div instructions do.

You still have to mark stmts with side-effects as volatile.

Conditional side-effects are tricky to get correct of course.