[Bug middle-end/126103] ranger: incoming range to a threading path is ignored

[aldy at quesejoda dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126103

--- Comment #15 from aldy at quesejoda dot com ---
   Ughhh this commit got tagged with a wrong PR. It's tangentially
   related. Sorry.
   On Aug 12, 2026 10:06, "cvs-commit at gcc dot gnu.org"
   <gcc-bugzilla@gcc.gnu.org> wrote:

     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126103

     --- Comment #14 from GCC Commits <cvs-commit at gcc dot gnu.org>
     ---
     The master branch has been updated by Aldy Hernandez
     <aldyh@gcc.gnu.org>:

     https://gcc.gnu.org/g:218575554420ded75052e56d5a89cd23522f20a7

     commit r17-3214-g218575554420ded75052e56d5a89cd23522f20a7
     Author: Aldy Hernandez <aldy@quesejoda.com>
     Date: Tue Aug 11 08:36:36 2026 +0000

     Thread paths ending in a computed goto

     The backward threader only handles paths ending in a GIMPLE_COND
     or
     GIMPLE_SWITCH, even though the profitability code and the generic
     copier already accounts for GIMPLE_GOTO. When we rewrote the
     backwards threader, the GIMPLE_GOTO handling was silently dropped
     because (a) ranger couldn't handle symbolics (b) DOM was picking
     our
     slack. Now with DOM removal in our sights, we need to handle
     computed
     gotos. This has been made trivial, by the recent work in prange
     providing points-to info.

     Note that a destination occurring in an abnormal PHI (when the
     goto
     block is itself one of the goto's targets) is still not handled.
     I'll
     be working on abnormal edge handling as a follow-up.

     Tested on ppc64le Linux.

     gcc/ChangeLog:

     PR tree-optimization/126103
     * tree-ssa-threadbackward.cc (class back_threader): Add
     find_taken_edge_goto.
     (back_threader::find_taken_edge): Handle GIMPLE_GOTO.
     (back_threader::find_taken_edge_goto): New.
     (back_threader::maybe_thread_block): Handle GIMPLE_GOTO.

     gcc/testsuite/ChangeLog:

     PR tree-optimization/126103
     * gcc.dg/pr89737.c: Add -fno-thread-jumps.
     * gcc.dg/tree-ssa/backthread-computed-goto-1.c: New test.
     * gcc.dg/tree-ssa/backthread-computed-goto-3.c: New test.

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