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tree-optimization/105679 - disable backward threading of unlikely entry

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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%]

	PR tree-optimization/105679
	* tree-ssa-threadbackward.cc
	(back_threader_profitability::profitable_path_p): Avoid threading
	when the entry edge is probably never executed.
This commit is contained in:
Richard Biener 2022-07-29 10:40:34 +02:00
parent b5f5d1b36e
commit 49ba4fdeb6
1 changed files with 9 additions and 0 deletions
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9
gcc/tree-ssa-threadbackward.cc
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@ -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)
{