[Bug tree-optimization/126464] [16/17 Regression] wrong code with FP ranges since r16-1108

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126464

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:3754582630fa1eeff44a39f656ba0c7db6e58d0d

commit r17-2814-g3754582630fa1eeff44a39f656ba0c7db6e58d0d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jul 30 09:56:41 2026 +0200

    range-op-float: Fix up inf handling in reverse narrowing float to float
cast [PR126464]

    The following testcase is miscompiled since my r16-1108 change.
    The problem is if we handle a reverse of a narrowing float to float cast
    (in the example there are double -> float and long double -> double
    cast) and the lhs range is [-inf, -inf] or [+inf, +inf] (note, regardless
    of whether some NaNs are allowed or not, so not necessarily
    lhs.known_isinf ()), then handling that range in the wider type also
    as [-inf, -inf] or [+inf, +inf] is wrong, e.g. for the double -> float
    conversion, [-inf, -0x0.ffffff8p+128] double range could map to just
    that [-inf, -inf].  We have already float_widen_lhs_range function
    but that just extends the range by +/-1ulp or 0.5ulp if the bounds
    are finite.  If the range isn't singleton (except for optional NaN),
    then the minimum (or maximum) finite is already in the range, so this just
    extends the case where they are singleton.
    I don't know how to portably figure out that 0x0.ffffff8p+128 for
    double -> float (especially when in float_widen_lhs_range we don't know
    yet the wider type), so the patch just uses the +/-1ulp extension (i.e.
    [-inf, min_finite] or [+inf, max_finite] case.

    2026-07-30  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/126464
            * range-op-float.cc (float_widen_lhs_range): Add also_inf argument
            defaulted to false, if true, extend even lb of +inf and ub of -inf.
            (operator_cast::op1_range): Adjust float_widen_lhs_range caller.

            * gcc.dg/pr126464.c: New test.

    Reviewed-by: Richard Biener <rguenth@suse.de>