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Subject: [Bug tree-optimization/30604] Unable to coalesce ssa_names <x>  and <y>  which are marked as MUST COALESCE
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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #11 from amacleod at redhat dot com  2007-11-09 15:37 -------
OK, new investigation show that using the smaller testcase firebird2-nav.cc
shows the inliner is misbehaving. 

before inlining  (*041t.profile):

  # BLOCK 2 freq:10000
  # PRED: ENTRY [100.0%]  (fallthru,exec)
  D.2709_4 = request_3(D)->req_pool;
  D.2710_5 = (struct blk *) D.2709_4;
  D.2711_6 = request_3(D)->req_transaction;
  D.2712_10 = VIO_get (tdbb_7(D), rpb_8(D), rsb_9(D), D.2711_6, D.2710_5);
  # SUCC: 4 (ab,eh,exec) 3 [100.0%]  (fallthru,exec)

  # BLOCK 3 freq:10000
  # PRED: 2 [100.0%]  (fallthru,exec)
  result_12(ab) = (BOOLEAN) D.2712_10;
<...>
  BTR_key (tdbb_7(D), D.2719_20, D.2718_19, D.2717_18, &value, 0B);
  goto <bb 5>;
  # SUCC: 4 (ab,eh,exec) 5 [100.0%]  (fallthru,exec)

  # BLOCK 4
  # PRED: 2 (ab,eh,exec) 3 (ab,eh,exec)
  # result_1(ab) = PHI <result_11(ab)(2), result_12(ab)(3)>
<L0>:;
  <...>

 # BLOCK 5 freq:10000
  # PRED: 3 [100.0%]  (fallthru,exec) 4 [100.0%]  (fallthru,exec)
  # result_2 = PHI <result_12(ab)(3), result_1(ab)(4)>
  return result_2;
  # SUCC: EXIT [100.0%]



and after inlining (*046i.inline) we see:



<bb 2>:

<bb 7>:
  D.2882_11 = request_9(D)->req_pool;
  D.2883_12 = (struct blk *) D.2882_11;
  D.2884_13 = request_9(D)->req_transaction;
  D.2885_14 = VIO_get (tdbb_8(D), rpb_3(D), rsb_1(D), D.2884_13, D.2883_12);

<bb 3>:
  result_15(ab) = (BOOLEAN) D.2885_14;
<...>
  BTR_key (tdbb_8(D), D.2892_22, D.2891_21, D.2890_20, &value, 0B);
  goto <bb 5>;

  # result_24(ab) = PHI <result_10(ab)(7), result_15(ab)(3)>
<L4>:;
<...>

<bb 5>:
  # result_23 = PHI <result_15(ab)(3), result_24(ab)(4)>
  if (result_23 != 0)
    goto <bb 6>;
  else
    goto <bb 7>;

<bb 6>:
  return 1;



Basic block 7 is missing a PHI node which should merge result_23 and result_10.
 The result of this missing PHI should then be used in block 5 instead of
result_10.

The way it currently sits, result 10 is live through basic block 3, which makes
it conflict with result_15, and makes the abnormal edges uncoalescable.

Someone familiar with the inliner can probably fix this quickly. I took a quick
look but its a different world in there :-)


-- 

amacleod at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jh at suse dot cz


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30604