On Wed, Nov 14, 2018 at 11:09 AM bin.cheng <bin.ch...@linux.alibaba.com> wrote:
>
> ------------------------------------------------------------------
> Sender:Richard Biener <richard.guent...@gmail.com>
> Sent at:2018 Nov 13 (Tue) 23:03
> To:bin.cheng <bin.ch...@linux.alibaba.com>
> Cc:GCC Patches <gcc-patches@gcc.gnu.org>
> Subject:Re: [PATCH PR84648]Adjust loop exit conditions for loop-until-wrap
> cases.
>
> >
> > On Sun, Nov 11, 2018 at 9:02 AM bin.cheng <bin.ch...@linux.alibaba.com>
> > wrote:
> >>
> >> Hi,
> >> This patch fixes PR84648 by adjusting exit conditions for loop-until-wrap
> >> cases.
> >> It only handles simple cases in which IV.base are constants because we
> >> rely on
> >> current niter analyzer which doesn't handle parameterized bound in wrapped
> >> case. It could be relaxed in the future.
> >>
> >> Bootstrap and test on x86_64 in progress.
> >
> > Please use TYPE_MIN/MAX_VALUE or wi::min/max_value consistently.
> > Either tree_int_cst_equal (iv0->base, TYPE_MIN_VALUE (type)) or
> > wide_int_to_tree (niter_type, wi::max_value (TYPE_PRECISION (type),
> > TYPE_SIGN (type))).
> >
> > Also
> >
> > + iv0->base = low;
> > + iv0->step = fold_convert (niter_type, integer_one_node);
> >
> > build_int_cst (niter_type, 1);
> >
> > + iv1->base = high;
> > + iv1->step = integer_zero_node;
> >
> > build_int_cst (niter_type, 0);
> Fixed, thanks for reviewing.
>
> >
> > With the code, what happens to signed IVs? I suppose we figure out things
> > earlier by means of undefined overflow?
> The code takes advantage of signed undefined overflow and handle it as wrap.
> In the reported test case, we have following IL:
> <bb 2> :
> goto <bb 4>; [INV]
>
> <bb 3> :
> i_4 = i_2 + 1;
>
> <bb 4> :
> # i_2 = PHI <0(2), i_4(3)>
> i.0_1 = (signed int) i_2;
> if (i.0_1 >= 0)
> goto <bb 3>; [INV]
> else
> goto <bb 5>; [INV]
>
> So the IV is actually transformed into signed int, we rely on scev to
> understand
> type conversion correctly and generate (int){0, 1} for i.0_1. Is this
> reasonable?
I think so.
> Updated patch attached, bootstrap and test on x86_64.
OK.
Thanks,
Richard.
> Thanks,
> bin
>
> 2018-11-11 Bin Cheng <bin.ch...@linux.alibaba.com>
>
> PR tree-optimization/84648
> * tree-ssa-loop-niter.c (adjust_cond_for_loop_until_wrap): New.
> (number_of_iterations_cond): Adjust exit cond for loop-until-wrap case
> by calling adjust_cond_for_loop_until_wrap.
>
> 2018-11-11 Bin Cheng <bin.ch...@linux.alibaba.com>
>
> PR tree-optimization/84648
> * gcc.dg/tree-ssa/pr84648.c: New test.
> * gcc.dg/pr68317.c: Add warning check on overflow.
