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.
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;
