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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/53957] Polyhedron 11 benchmark: MP_PROP_DESIGN twice as long as other compiler
Date: Wed, 18 Jul 2012 12:09:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53957

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |fortran

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-18 12:09:23 UTC ---
The issue seems to be that the frontend uses two induction variables, one
signed
and one unsigned, for

                        DO i = 1 , 1 + NINT(2.0D0*PI*trns/dphit) ,      &
     &                     NINT(ainc/(dphit*(180.0D0/PI)))
...
                        END DO

<bb 78>:
  # i_5 = PHI <[mp_prop_design.f90 : 697:0] 1(77), [mp_prop_design.f90 : 696:0]
i_621(79)>
  # countm1.38_32 = PHI <[mp_prop_design.f90 : 696:0] countm1.38_466(77),
[mp_prop_design.f90 : 696:0] countm1.38_622(79)>
  # prephitmp.386_3285 = PHI <pretmp.385_3284(77), D.2618_614(79)>
  # prephitmp.386_3287 = PHI <pretmp.385_3286(77), D.2620_620(79)>
...
  [mp_prop_design.f90 : 696:0] i_621 = i_5 + pretmp.378_3242;
  [mp_prop_design.f90 : 696:0] # DEBUG i => i_621
  [mp_prop_design.f90 : 696:0] if (countm1.38_32 == 0)
    goto <bb 80>;
  else
    goto <bb 79>;

<bb 79>:
  [mp_prop_design.f90 : 696:0] countm1.38_622 = countm1.38_32 + 4294967295;
  [mp_prop_design.f90 : 696 : 0] goto <bb 78>;

and the "decrement" of countm1 happens in the loop latch block.  It would
be better to have this similar to other loops I see,

       bool flag = end-value == i;
       i = i + 1;
       if (flag) goto loop_exit;