On Tue, Feb 13, 2018 at 12:41:28AM +0100, Paolo Bonzini wrote:
> On 09/02/2018 19:07, Jakub Jelinek wrote:
> > On Fri, Feb 09, 2018 at 07:01:08PM +0100, Richard Biener wrote:
> >>> which indeed fixes the testcase and seems not to break asan.exp.
> >>
> >> Huh. Need to double check why that makes sense ;)
> >
> > I think it does, for both ASAN_CHECK and ASAN_MARK the pointer argument
> > is the second one, the first one is an integer argument with flags.
> > And ASAN_MARK, both poison and unpoison, works kind like a clobber on the
> > referenced variable, before unpoison it is generally inaccessible and after
> > poison too.
>
> This was too optimistic. :(
>
> In use-after-scope-types-1.C, after the patch FRE+DSE are able to
> optimize away the problematic read. In general it seems to me that the
> sanitizer passes should be before DSE if we want ASAN builtins to have
> precise info, otherwise some reads or stores might not be
> instrumented---GCC was being lucky here.
>
> The obvious change here is:
That is way too early, I don't think this is a good idea.
Certainly not in stage4.
Jakub
