[Bug fortran/66459] bogus warning 'w.offset' may be used uninitialized in this function [-Wmaybe-uninitialized]

["manu at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66459

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |manu at gcc dot gnu.org

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
If you do

gfortran -Wuninitialized test.f90 -fdump-tree-all-all-lineno -O1

and look at test.f90.162t.uninit1, we see:

  # .MEM_24 = PHI <.MEM_15(D)(28), .MEM_68(37)>
  # w$dim$1$stride_46 = PHI <w$dim$1$stride_85(D)(28), [test.f90:9:0]
w$dim$1$stride_22(37)>
  # w$offset_26 = PHI <w$offset_16(D)(28), [test.f90:9:0] w$offset_56(37)>

but this code is transformed by optimization. The unoptimized SSA contains:

  [test.f90:9:0] # VUSE <.MEM_18>
  _22 = [test.f90:9:0] *m_21(D);
  [test.f90:9:0] _23 = MAX_EXPR <_22, 0>;
  [test.f90:9:0] _24 = (integer(kind=8)D.9) _23;
...
  [test.f90:9:0] _39 = _24;
...
  [test.f90:9:0] _68 = ~_39;
...
  [test.f90:9:0] wD.3400.offsetD.3387 = _68;

and the gimple generated by Fortran contains something similar:

            [test.f90:9:0] D.3429 = [test.f90:9:0] *mD.3381;
            [test.f90:9:0] D.3430 = MAX_EXPR <D.3429, 0>;
            [test.f90:9:0] D.3402 = (integer(kind=8)D.9) D.3430;

It seems that *mD.3381 is not initialized.

(It is very strange that gfortran converts user-defined variables to lowercase.
It makes reading the dumps more difficult. It also does many unnecessary
copies, making the code harder to analyze.)