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References: <bug-38497-6528@http.gcc.gnu.org/bugzilla/>
Subject: [Bug tree-optimization/38497] PRE missing a load PRE which causes a loop to have two BBs
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From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #5 from rguenth at gcc dot gnu dot org  2010-03-03 11:03 -------
I'm not so sure.  We start with

<bb 2>:
  plaintextlen_3 = *a_2(D);

<bb 3>:
  # i_13 = PHI <i_6(5), 0(2)>
  D.2725_5 = *a_2(D);
  DoHuffIteration (D.2725_5);
  i_6 = i_13 + 1;
  if (i_6 <= 9999)
    goto <bb 5>;
  else
    goto <bb 4>;

<bb 5>:
  goto <bb 3>;

<bb 4>:
  D.2725_7 = *a_2(D);

so *a_2 (4) is antic-out in bb3 but dies in bb3 (thus it's not antic-in there).
*a_2 (3) is antic-in in bb5 and available in bb2.  Thus we insert in bb5:

<bb 2>:
  plaintextlen_3 = *a_2(D);

<bb 3>:
  # i_13 = PHI <i_6(5), 0(2)>
  # prephitmp.3_14 = PHI <pretmp.2_1(5), plaintextlen_3(2)>
  D.2725_5 = prephitmp.3_14;
  DoHuffIteration (D.2725_5);
  i_6 = i_13 + 1;
  if (i_6 <= 9999)
    goto <bb 5>;
  else
    goto <bb 4>;

<bb 5>:
  pretmp.2_1 = *a_2(D);
  goto <bb 3>;

<bb 4>:
  D.2725_7 = *a_2(D);

now what is left is hoisting *a_2(D) to after the call.  But that's not PRE.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38497