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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/106661] New: possible uninitialized variable usage
 in store_bit_field_1
Date: Tue, 16 Aug 2022 23:59:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106661

            Bug ID: 106661
           Summary: possible uninitialized variable usage in
                    store_bit_field_1
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Compiling the trunk with GCC 7.5.0 for a cross to riscv32-linux-gnu produces
the following warning:
In file included from
/bajas/pinskia/src/toolchain-riscv/scripts/../src/gcc/coretypes.h:475:0,
                 from
/bajas/pinskia/src/toolchain-riscv/scripts/../src/gcc/expmed.cc:26:
/bajas/pinskia/src/toolchain-riscv/scripts/../src/gcc/poly-int.h: In functi=
on
=E2=80=98bool store_bit_field_1(rtx, poly_uint64, poly_uint64, poly_uint64,
poly_uint64, machine_mode, rtx, bool, bool, bool)=E2=80=99:
/bajas/pinskia/src/toolchain-riscv/scripts/../src/gcc/poly-int.h:1107:38:
warning: =E2=80=98regnum=E2=80=99 may be used uninitialized in this function
[-Wmaybe-uninitialized]
     POLY_SET_COEFF (C, r, i, NCa (a) * b.coeffs[i]);
                                      ^
/bajas/pinskia/src/toolchain-riscv/scripts/../src/gcc/expmed.cc:797:21: not=
e:
=E2=80=98regnum=E2=80=99 was declared here
       HOST_WIDE_INT regnum;
                     ^~~~~~


I looked into the code I think the warning is correct, regnum could be
uninitialized if undefined_p is true but constant_multiple_p returns false.
I have not looked into if the warning happens for the trunk or why x86_64 d=
oes
not get the warning.=