On Mon, 7 Dec 2020, Richard Sandiford wrote:
> Richard Biener <rguent...@suse.de> writes:
> > This avoids the degenerate case of a TYPE_MAX_VALUE latch iteration
> > count value causing wrong range info for the vector IV. There's
> > still the case of VF == 1 where if we don't know whether we hit the
> > above case we cannot emit a range.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> >
> > 2020-12-07 Richard Biener <rguent...@suse.de>
> >
> > PR tree-optimization/98117
> > * tree-vect-loop-manip.c (vect_gen_vector_loop_niters):
> > Properly handle degenerate niter when setting the vector
> > loop IV range.
> >
> > * gcc.dg/torture/pr98117.c: New testcase.
> > ---
> > gcc/testsuite/gcc.dg/torture/pr98117.c | 19 +++++++++++++++++
> > gcc/tree-vect-loop-manip.c | 28 ++++++++++++++++++++------
> > 2 files changed, 41 insertions(+), 6 deletions(-)
> > create mode 100644 gcc/testsuite/gcc.dg/torture/pr98117.c
> >
> > diff --git a/gcc/testsuite/gcc.dg/torture/pr98117.c
> > b/gcc/testsuite/gcc.dg/torture/pr98117.c
> > new file mode 100644
> > index 00000000000..f2160257263
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/torture/pr98117.c
> > @@ -0,0 +1,19 @@
> > +/* { dg-do run } */
> > +/* { dg-additional-options "-fno-tree-scev-cprop" } */
> > +
> > +unsigned char c;
> > +void __attribute__((noipa))
> > +e()
> > +{
> > + do
> > + {
> > + }
> > + while (++c);
> > +}
> > +int main()
> > +{
> > + e();
> > + if (c != 0)
> > + __builtin_abort ();
> > + return 0;
> > +}
> > diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
> > index 36179188f6d..2370b879b21 100644
> > --- a/gcc/tree-vect-loop-manip.c
> > +++ b/gcc/tree-vect-loop-manip.c
> > @@ -2034,13 +2034,29 @@ vect_gen_vector_loop_niters (loop_vec_info
> > loop_vinfo, tree niters,
> > niters_vector = force_gimple_operand (niters_vector, &stmts, true,
> > var);
> > gsi_insert_seq_on_edge_immediate (pe, stmts);
> > /* Peeling algorithm guarantees that vector loop bound is at least
> > ONE,
> > - we set range information to make niters analyzer's life easier. */
> > + we set range information to make niters analyzer's life easier.
> > + Note the number of latch iteration value can be TYPE_MAX_VALUE so
> > + we have to represent the vector niter TYPE_MAX_VALUE + 1 >> log_vf. */
> > if (stmts != NULL && log_vf)
> > - set_range_info (niters_vector, VR_RANGE,
> > - wi::to_wide (build_int_cst (type, 1)),
> > - wi::to_wide (fold_build2 (RSHIFT_EXPR, type,
> > - TYPE_MAX_VALUE (type),
> > - log_vf)));
> > + {
> > + if (niters_no_overflow)
> > + set_range_info (niters_vector, VR_RANGE,
> > + wi::one (TYPE_PRECISION (type)),
> > + wi::rshift (wi::max_value (TYPE_PRECISION (type),
> > + TYPE_SIGN (type)),
> > + exact_log2 (const_vf),
> > + TYPE_SIGN (type)));
> > + /* For VF == 1 the vector IV might also overflow so we cannot
> > + assert a minimum value of 1. */
> > + else if (const_vf > 1)
>
> This code is common to const vf and non-const vf, so const_vf isn't
> guaranteed to be valid.
It's guarded with log_vf != NULL which we only set in the
constant vf case.
Richard.
> Thanks,
> Richard
>
> > + set_range_info (niters_vector, VR_RANGE,
> > + wi::one (TYPE_PRECISION (type)),
> > + wi::rshift (wi::max_value (TYPE_PRECISION (type),
> > + TYPE_SIGN (type))
> > + - (const_vf - 1),
> > + exact_log2 (const_vf), TYPE_SIGN (type))
> > + + 1);
> > + }
> > }
> > *niters_vector_ptr = niters_vector;
> > *step_vector_ptr = step_vector;
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
