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Subject: [Bug middle-end/60429] [4.7/4.8/4.9 Regression] Miscompilation (aliasing) with -finline-functions
Date: Mon, 10 Mar 2014 10:42:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60429

--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> ---
Seems to be a PTA issue:

InsertionSort_pETEchase.29_82, points-to vars: { }
InsertionSort_pETEchase.29_86, points-to non-local, points-to escaped,
points-to vars: { }
p1_155, points-to NULL, points-to vars: { }

  <bb 30>:
  InsertionSort_pETEchase.29_82->next = p1_84;
  p1_155->next = InsertionSort_pETEchase.28_85;
  InsertionSort_pETEchase.29_86 = InsertionSort_pETEchase.28_85->back;
  InsertionSort_pETEchase.29_86->next = p1_155;
  p1_155->back = &InsertionSort_pETEchaseBackTMP;

taking _155 as example

  # p1_155 = PHI <_35(57), p1_58(60)>

_35, points-to NULL, points-to vars: { }
p1_58, points-to vars: { }

  _35 = MEM[(struct _EdgeTableEntry * *)&AET + 16B];

  # p1_58 = PHI <p1_84(59), p1_84(30), p1_87(34)>

  p1_84 = p1_155->next;
  p1_87 = p1_155->next;

so it's a cycle seeded only by MEM[(struct _EdgeTableEntry * *)&AET + 16B];

_35 = { NULL } same as AET.128+64

_35 = AET.128+64

  # p1_150 = PHI <&AET(47), p1_151(49)>
  # p1_151 = PHI <p1_19(47), p1_45(49)>
  p1_45 = p1_151->next;
  fn3_tmp = p1_45;
  p1_151->next = p1_47;
  p1_151->back = p1_150;

p1_150 = &AET.0+96
*p1_150 + 128 = p1_151


Note that valgrind shows loads of errors (with the reduced testcase at least)
that show invalid reads and writes even at -O0.  So we may just optimistically
optimize based on that undefined behavior.

At least I can't see anything wrong with what PTA derives ...