The following makes the backward threader reject threads whose entry edge is probably never executed according to the profile. That in particular, for the testcase, avoids threading the irq == 1 check on the path where irq > 31, thereby avoiding spurious -Warray-bounds diagnostics
if (irq_1(D) > 31) goto <bb 3>; [0.00%] else goto <bb 4>; [100.00%] ;; basic block 3, loop depth 0, count 0 (precise), probably never executed _2 = (unsigned long) irq_1(D); __builtin___ubsan_handle_shift_out_of_bounds (&*.Lubsan_data0, 1, _2); _3 = 1 << irq_1(D); mask_4 = (u32) _3; entry = instance_5(D)->array[irq_1(D)]; capture (mask_4); if (level_6(D) != 0) goto <bb 7>; [34.00%] else goto <bb 5>; [66.00%] ;; basic block 5, loop depth 0, count 708669600 (estimated locally), maybe hot if (irq_1(D) == 1) goto <bb 7>; [20.97%] else goto <bb 6>; [79.03%] Bootstrap and regtest running on x86_64-unknown-linux-gnu. The testcase in the PR requries both ubsan and sancov so I'm not sure where to put it but IIRC there were quite some duplicate PRs wrt threading unlikely paths exposing diagnostics, eventually some testcase will come out of those (when we identify them). Note the patch is quite conservative in only disabling likely never executed paths rather than requiring maybe_hot_edge_p (OTOH those are somewhat similar in the end). I'm going to push it when testing finishes but maybe there are some testcases to adjust. PR tree-optimization/105679 * tree-ssa-threadbackwards.cc (back_threader_profitability::profitable_path_p): Avoid threading when the entry edge is probably never executed. --- gcc/tree-ssa-threadbackward.cc | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/gcc/tree-ssa-threadbackward.cc b/gcc/tree-ssa-threadbackward.cc index 3519aca84cd..90f5331c265 100644 --- a/gcc/tree-ssa-threadbackward.cc +++ b/gcc/tree-ssa-threadbackward.cc @@ -777,6 +777,15 @@ back_threader_profitability::profitable_path_p (const vec<basic_block> &m_path, "exceeds PARAM_MAX_FSM_THREAD_PATH_INSNS.\n"); return false; } + edge entry = find_edge (m_path[m_path.length () - 1], + m_path[m_path.length () - 2]); + if (probably_never_executed_edge_p (cfun, entry)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, " FAIL: Jump-thread path not considered: " + "path entry is probably never executed.\n"); + return false; + } } else if (!m_speed_p && n_insns > 1) { -- 2.35.3