[Bug c++/94905] New: Bogus warning -Werror=maybe-uninitialized

[bug-apl at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94905

            Bug ID: 94905
           Summary: Bogus warning -Werror=maybe-uninitialized
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bug-apl at gnu dot org
  Target Milestone: ---

Hi,

as of g++ 9.3.0 when building GNU APL, g++ emits bogus warnings of type
-Werror=maybe-uninitialized.

Apparently the compiler issues these warnings simply because it is lacking
enough context to really figure out what is happening (e.g. if the supposedly
missing initialization is happening in a different function).

An example is:

https://svn.savannah.gnu.org/viewvc/apl/trunk/src/Shape.hh?view=markup

Shape.hh:133:18: error: ‘shape_Z.Shape::rho[axis]’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
         if (rho[r])   { volume /= rho[r];  rho[r] = sh;  volume *=
rho[r]; }
             ~~~~~^

The line 133 is preceded by an assertion that verifies that rho[r] is
initialized. Apparently the compiler assumes that the initialization
of rho[r] on the right of = happens after the test of rho[r] on the left
of =. It completely ignores, however, the fact that rho[r] was simply
updated and was initialized already before the function (set_shape_item)
was called.

May I kindly request to move this kind of warnings away from -Wall to
-Wextra ?

According to "man g++":

      -Wall
           This enables all the warnings about constructions that some users
           consider questionable, and that are easy to avoid (or modify to
           prevent the warning), even in conjunction with macros.  This also

In the example above there is no "easy to avoid" way to fix the warning.

Kind regards,
Jürgen Sauermann
Maintainer of GNU APL