This revives an earlier patch since the problematic code applying
extra costs to PHIs in copied blocks we couldn't make any sense of
prevents a required threading in this case. Instead of coming up
with an artificial other costing the following simply removes the
bits.
As with all threading changes this requires a plethora of testsuite
adjustments, but only the last three are unfortunate as is the
libgomp team.c adjustment which is required to avoid a bogus -Werror
diagnostic during bootstrap.
PR tree-optimization/111294
gcc/
* tree-ssa-threadbackward.cc (back_threader_profitability::m_name):
Remove
(back_threader::find_paths_to_names): Adjust.
(back_threader::maybe_thread_block): Likewise.
(back_threader_profitability::possibly_profitable_path_p): Remove
code applying extra costs to copies PHIs.