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Subject: [Bug middle-end/50628] [4.7 Regression] gfortran.fortran-torture/execute/entry_4.f90 fails
Date: Wed, 23 Nov 2011 16:41:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50628

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jamborm at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #11 from Martin Jambor <jamborm at gcc dot gnu.org> 2011-11-23 16:01:37 UTC ---
What happens in SRA is this.  This a part of the dump before SRA
(ealias):

<bb 2>:
  D.2127_5 = *a_1(D);
  if (D.2127_5 > 0)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  D.2126_6 = D.2127_5 <= 45;
  /* In the following statement SRA notices a logical access
     to __result_master.1.f2. */
  __result_master.1.f2.e2 = D.2126_6; 
  goto <bb 5>;

<bb 4>:
  /* In the following statement SRA notices a complex access
     to __result_master.1.f2.  If a scalar type access has a scalar type
     sub-access, they cannot be made into replacements.  */
  __result_master.1.f2.f2 = __complex__ (4.5e+1, 0.0);

<bb 5>:

  /* However, before SRA figures that out, it propagates the logical
  sub-accesses across the following aggregate assignment in order to
  facilitate pseudo copy propagation of aggregates.  Thus, D.2125 gets an
  artificial logical sub-access which is a child of an aggregate and qualifies
  for replacement creation.  And that's why the weird logical variable gets
  there.  */

  D.2125 = __result_master.1.f2;
  __result_master.1.f2 ={v} {CLOBBER};
  __result = D.2125;
  D.2056_2 = __result.f2;
}

We should not do propagation of sub-accesses of scalar accesses because
that's never profitable and it would also fix this testcase.

However, I'm afraid that if we encapsulated 

  __result_master.1.f2.f2 = __complex__ (4.5e+1, 0.0);

into the union type and moved the last two statements of the function
into a different function, we would get the logical replacements of
__result_master.1.f2 and D.2125 again and might incur the same problems
(depending on whether FRE would be able to look through this).
SRA on unions and type-conversions is tough.