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Re: [PATCH 3/5] timevar.h: Add an auto_timevar class


On Tue, 2014-10-14 at 11:03 +0200, Richard Biener wrote:
> On Mon, Oct 13, 2014 at 7:45 PM, David Malcolm <dmalcolm@redhat.com> wrote:
> > This is used in a couple of places in jit/jit-playback.c to ensure
> > that we pop the timevar on every exit path from a function.
> >
> > I could rewrite them if need be, but it does simplify things.
> 
> Sorry to be bikeshedding but auto_timevar sounds odd - this is
> just a one-element timevar stack.

Sorry that the usage examples didn't make it through in my original
email; these are in patch 06/10 in gcc/jit/jit-playback.c and look like
this:

playback::context::
compile ()
{
  ... lots of code...

  {
    auto_timevar assemble_timevar (TV_ASSEMBLE);

    ... lots of code, with multiple return paths...

  }

}

the idea being that the timevar_pop happens implicitly at the exit from
the scope (e.g. via one of the error-handling returns).

FWIW I rather like the current name: I think of it as an RAII-style way
of not having to manually call timevar_pop.

The "auto_" prefix to me evokes both such RAII types as "auto_ptr" and
"auto_vec", and the fact that it's intended to be on the stack i.e. have
"auto" storage class.

> Don't have a real better name though :/  Maybe timevar_pushpop ?
> 
> Otherwise this looks ok.
> 
> Thanks,
> Richard.
> 
> > Written by Tom Tromey.
> >
> > gcc/ChangeLog:
> >         * timevar.h (class auto_timevar): New class.
> > ---
> >  gcc/timevar.h | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/gcc/timevar.h b/gcc/timevar.h
> > index 6703cc9..f018e39 100644
> > --- a/gcc/timevar.h
> > +++ b/gcc/timevar.h
> > @@ -110,6 +110,30 @@ timevar_pop (timevar_id_t tv)
> >      timevar_pop_1 (tv);
> >  }
> >
> > +// This is a simple timevar wrapper class that pushes a timevar in its
> > +// constructor and pops the timevar in its destructor.
> > +class auto_timevar
> > +{
> > + public:
> > +  auto_timevar (timevar_id_t tv)
> > +    : m_tv (tv)
> > +  {
> > +    timevar_push (m_tv);
> > +  }
> > +
> > +  ~auto_timevar ()
> > +  {
> > +    timevar_pop (m_tv);
> > +  }
> > +
> > + private:
> > +
> > +  // Private to disallow copies.
> > +  auto_timevar (const auto_timevar &);
> > +
> > +  timevar_id_t m_tv;
> > +};
> > +
> >  extern void print_time (const char *, long);
> >
> >  #endif /* ! GCC_TIMEVAR_H */
> > --
> > 1.8.5.3
> >



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