BTW, we should probably backport this to god knows how many branches.
Aldy
On Tue, May 23, 2023 at 2:58 PM Aldy Hernandez <al...@redhat.com> wrote:
>
> [Andrew, do you remotely remember what if anything this did? It came
> from a wholesale merge from our long forgotten branch, so there's no
> history on the specifics of it. Not important, I'm just curious. It
> was probably me high on something.]
>
> This patch removes a buggy special case in irange::invert which seems
> to have been broken for a while, and probably never triggered because
> the legacy code was handled elsewhere, and the non-legacy code was
> using an int_range_max of int_range<255> which made it extremely
> likely for num_ranges == 255. However, with auto-resizing ranges,
> int_range_max will start off at 3 and can hit this bogus code in the
> unswitching code.
>
> PR tree-optimization/109934
>
> gcc/ChangeLog:
>
> * value-range.cc (irange::invert): Remove buggy special case.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr109934.c: New test.
> ---
> gcc/testsuite/gcc.dg/tree-ssa/pr109934.c | 22 ++++++++++++++++++++++
> gcc/value-range.cc | 8 --------
> 2 files changed, 22 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr109934.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr109934.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr109934.c
> new file mode 100644
> index 00000000000..08bd5ce95c6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr109934.c
> @@ -0,0 +1,22 @@
> +// { dg-do run }
> +// { dg-options "-O3" }
> +
> +int printf(const char *, ...);
> +short a;
> +long b = 3, c;
> +int d(int e) {
> + switch (e)
> + case 111:
> + case 222:
> + case 44:
> + return 0;
> + return e;
> +}
> +int main() {
> + for (; a >= 0; --a)
> + if (d(c + 23) - 23)
> + b = 0;
> +
> + if (b != 3)
> + __builtin_abort ();
> +}
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index 45b1e655967..874a1843ebf 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -1650,14 +1650,6 @@ irange::invert ()
> wide_int type_min = wi::min_value (prec, sign);
> wide_int type_max = wi::max_value (prec, sign);
> m_nonzero_mask = wi::minus_one (prec);
> - if (m_num_ranges == m_max_ranges
> - && lower_bound () != type_min
> - && upper_bound () != type_max)
> - {
> - m_base[1] = type_max;
> - m_num_ranges = 1;
> - return;
> - }
>
> // At this point, we need one extra sub-range to represent the
> // inverse.
> --
> 2.40.1
>
