[Bug tree-optimization/103690] [12 Regression] ICE: in build2, at tree.c:4985 with -g -O2 -fno-tree-dce -fno-tree-dse -fno-tree-fre --param=max-jump-thread-duplication-stmts=94 since r12-2591-g2e96b5f14e402569

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103690

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Value numbering stmt = __trans_tmp_1_14 = _24 + 4;
Setting value number of __trans_tmp_1_14 to __trans_tmp_1_22 (changed)

what we do is avoiding useless work during elimination, not visiting if (0)
guarded code - those regions will have not up-to-date SSA form.

Block 14: BB5 found not executable

the issue is that PRE does

  /* Because we don't follow exactly the standard PRE algorithm, and decide not
     to insert PHI nodes sometimes, and because value numbering of casts isn't
     perfect, we sometimes end up inserting dead code.   This simple DCE-like
     pass removes any insertions we made that weren't actually used.  */
  simple_dce_from_worklist (inserted_exprs);

which eventually runs into those uses for expressions we inserted into those
unreachable blocks.

The issue is long latent I think.