This error/warning has been seen on newer gcc versions on openjdk 11:
In function 'mp_zero',
    inlined from 'mp_zero' at /home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c:316:8,
    inlined from 'mp_set_int' at /home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c:353:3,
    inlined from 'mp_cmp_int' at /home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c:1735:26:
/home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c:321:3: error: 'tmp.dp' may be used uninitialized [-Werror=maybe-uninitialized]
  321 | s_mp_setz(DIGITS(mp), ALLOC(mp));
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c: In function 'mp_cmp_int':
/home/tester/temurinbuild-1757944128/workspace/build/src/src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c:1730:11: note: 'tmp' declared here
 1730 | mp_int tmp;
      | ^~~

Problem does not affect newer jdks, because affected code was removed by JDK-8235710.

Also whether warning/error is generated depends on other conditions like compiler version / arch / build kind etc. Seems like compiler needs to do enough inlining to detect this, as analysis need to cross function boundary.