On Fri, 15 Nov 2024, Richard Biener wrote:
> When trying to change a IV from IV0 < IV1 to IV0' != IV1' we apply
> fancy adjustments to the may_be_zero condition we compute rather
> than using the obvious IV0->base >= IV1->base expression (to be
> able to use > instead of >=?). This doesn't seem to go well.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Can anybody think of what the adjustment by mod is about?
I have now pushed this.
Richard.
> Thanks,
> Richard.
>
> PR tree-optimization/117574
> * tree-ssa-loop-niter.cc (number_of_iterations_lt_to_ne):
> Use the obvious may_be_zero condition.
>
> * gcc.dg/torture/pr117574-1.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/torture/pr117574-1.c | 20 +++++++++++++++
> gcc/tree-ssa-loop-niter.cc | 31 +++++------------------
> 2 files changed, 27 insertions(+), 24 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr117574-1.c
>
> diff --git a/gcc/testsuite/gcc.dg/torture/pr117574-1.c
> b/gcc/testsuite/gcc.dg/torture/pr117574-1.c
> new file mode 100644
> index 00000000000..2e99cec13b6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr117574-1.c
> @@ -0,0 +1,20 @@
> +/* { dg-do run } */
> +
> +void abort (void);
> +int a, c;
> +long b;
> +short d;
> +static long e(long f, long h, long i) {
> + for (long g = f; g <= h; g += i)
> + b += g;
> + return b;
> +}
> +int main() {
> + c = 1;
> + for (; c >= 0; c--)
> + ;
> + for (; e(d + 40, d + 76, c + 51) < 4;)
> + ;
> + if (a != 0)
> + abort ();
> +}
> diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
> index 9518bf969cd..1be4b552206 100644
> --- a/gcc/tree-ssa-loop-niter.cc
> +++ b/gcc/tree-ssa-loop-niter.cc
> @@ -1200,17 +1200,6 @@ number_of_iterations_lt_to_ne (tree type, affine_iv
> *iv0, affine_iv *iv1,
> if (integer_zerop (assumption))
> return false;
> }
> - if (mpz_cmp (mmod, bnds->below) < 0)
> - noloop = boolean_false_node;
> - else if (POINTER_TYPE_P (type))
> - noloop = fold_build2 (GT_EXPR, boolean_type_node,
> - iv0->base,
> - fold_build_pointer_plus (iv1->base, tmod));
> - else
> - noloop = fold_build2 (GT_EXPR, boolean_type_node,
> - iv0->base,
> - fold_build2 (PLUS_EXPR, type1,
> - iv1->base, tmod));
> }
> else
> {
> @@ -1226,21 +1215,15 @@ number_of_iterations_lt_to_ne (tree type, affine_iv
> *iv0, affine_iv *iv1,
> if (integer_zerop (assumption))
> return false;
> }
> - if (mpz_cmp (mmod, bnds->below) < 0)
> - noloop = boolean_false_node;
> - else if (POINTER_TYPE_P (type))
> - noloop = fold_build2 (GT_EXPR, boolean_type_node,
> - fold_build_pointer_plus (iv0->base,
> - fold_build1 (NEGATE_EXPR,
> - type1,
> tmod)),
> - iv1->base);
> - else
> - noloop = fold_build2 (GT_EXPR, boolean_type_node,
> - fold_build2 (MINUS_EXPR, type1,
> - iv0->base, tmod),
> - iv1->base);
> }
>
> + /* IV0 < IV1 does not loop if IV0->base >= IV1->base. */
> + if (mpz_cmp (mmod, bnds->below) < 0)
> + noloop = boolean_false_node;
> + else
> + noloop = fold_build2 (GE_EXPR, boolean_type_node,
> + iv0->base, iv1->base);
> +
> if (!integer_nonzerop (assumption))
> niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
> niter->assumptions,
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
