[Bug middle-end/57904] [4.9 Regression] Bogus(?) "invokes undefined behavior" warning with Fortran's finalization wrapper (gfortran.dg/class_48.f90)

[bernd.edlinger at hotmail dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57904

--- Comment #13 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Jakub Jelinek from comment #12)
> But you can always create testcases (in C/C++ etc.) that will hit this
> warning, so while the FE change is possible, we need to do something either
> about the optimization passes in between IPA and cunrolli (copyprop change
> Jeff talks about, perhaps only done for that single pass instance and not
> others, or all?, guess depending on how expensive it is) or scheduling there
> another instance of some other cleanup pass, or deferring the warning
> reporting until some cleanup.
> 

Could someone please provide a C test case that generates this warning?

maybe something like:

 int dovar = from;
 if (dovar <= to)
   for (;;)
     {
      ...
      if (dovar == to)
        break;
      dovar += step;
    }

> For the FE change, I guess most important are benchmark results, doesn't it
> slow down important benchmarks?


I think the change in the simple DO-loops really makes sense,
independent of this warning.

It generates the IL code just a bit more like it is done in C:

for (dovar=from; dovar <= to; dovar+=step) { ... }

=>

 dovar = from;
 if (dovar <= to)
 {
   loop:
    ...
    dovar+=step;
    if (dovar <= to)
       goto loop;
 }

Therefore the IL is easier to analyze and 
chances are good that the optimizer performs better.

I can't do these benchmarks however. Who could do that for us?