On Wed, Oct 16, 2019 at 4:55 PM Luis Machado <luis.mach...@linaro.org> wrote:
>
> On 10/16/19 5:59 AM, Richard Biener wrote:
> > I think that adding an extra jump is unwanted. Instead - if you disregard
> > the single-source-line case - there's always the jump and the label we jump
> > to which might/should get different source locations. Like in one of the
> > above
> > cases:
> >
> > main ()
> > {
> > int D.1803;
> >
> > [t.c:2:1] {
> > int var;
> >
> > [t.c:3:5] var = 0;
> > <D.1801>:
> > [t.c:7:8] var = var + 1;
> > [t.c:7:8] goto <D.1801>;
> > [t.c:10:8] D.1803 = 0;
> > [t.c:10:8] return D.1803;
> >
> > seen at GIMPLE. Of course we lose the label once we build the CFG,
> > but we retain a goto-locus which we could then put back on the
> > jump statement. For this case we at the moment get
> >
> > .L2:
> > .loc 1 7 0 discriminator 1
> > addl $1, -4(%rbp)
> > jmp .L2
> >
> > and we could do
> >
> > .L2:
> > .loc 1 7 0 discriminator 1
> > addl $1, -4(%rbp)
> > .loc 1 5 0
> > jmp .L2
> >
> > thus assign the "destination" location to the jump instruction?
>
> On a first look, i considered reusing the jump instruction that did not
> get a location assigned to it, but that didn't work right for all cases,
> such as the one you showed below with the incorrect line ordering.
>
> >
> > The first question is of course what happens with the edges
> > goto_locus at the moment and why we get the code we get.
> >
> > The above solution might also be a bit odd since for the loop
> > entry we'd first see line 7 and only after that line 5. But fixing
> > that would mean we have to output an extra instruction
> > (where I'd chose a nop instead of some random extra jump).
>
> Right. I wanted to preserve the correct order of execution, at least
> from a O0 perspective. A nop would work just as well. I'll give this a try.
>
> I don't think it makes sense to output additional instructions in O1+
> cases just because we want to have more debug info, but we do need a new
> instruction address in some cases, in order to use it in the line table
> for the line transition.
>
> Would it make sense to have it restricted to O0?
Generation of an extra NOP? Sure. For O1+ we may want to give
the jump a different location though?
Richard.
