Re: enable -Wformat-truncation with -Og (PR 79691)

[Martin Sebor <msebor@gmail.com>]

On 02/24/2017 03:10 AM, Richard Biener wrote:
> On Fri, Feb 24, 2017 at 1:35 AM, Martin Sebor <msebor@gmail.com> wrote:
>> Bug 79691 - -Wformat-truncation suppressed by (and only by) -Og
>> points out that the gimple-ssa-sprintf pass doesn't run when
>> this optimization option is used.  That's because I forgot to
>> add it to the set of optimization passes that run with that
>> option.  The attached trivial patch tested on x86_64 corrects
>> the oversight.
>>
>> Is this okay for 7.0?
>
> Any reason for the placement before copy-prop?  I'd have done it
> after pass_late_warn_uninitialized for example.

I wanted to make sure that folded sprintf return values would be
eligible for further copy propagation.  E.g., that a + b would
be folded into a constant:

   int foo (void)
   {
     int a = snprintf (0, 0, "%i", 123);
     int b = snprintf (0, 0, "%i", 1234);
     return a + b;
   }

But I could have easily missed some important use case where this
placement will compromise the warning.  I don't have any tests
for this one way or the other so I'm happy to go with your
recommendation.  Let me know which you think is more appropriate
(if you have a suggestion for a test case I'd be grateful).

>
> Also doesn't pass_sprintf_length rely on get_range_info ()?  With -Og
> nothing populates those so you'll always get effectively VARYING ranges.

It does when it's available but as Jakub noted, it works without
it as well (at -O0).

Thanks
Martin