The test case below shows that suppressing -Wuninitialized by #pragma GCC diagnostic doesn't work the same as it does for other warnings (-Wrray-bounds in this instance, but most other warnings behave like it).  This makes it difficult for users to control -Wuninitialized (and -Wmaybe-uninitialized), compounding their frustration when they run into one of its false positives.

The reason for the difference is that tree-ssa-uninit.c calls linemap_resolve_location (line_table, location, LRK_SPELLING_LOCATION, NULL) before using location, which other warnings don't do.  The call was introduced in r186971 along with a test for its effect, gcc.dg/cpp/pragma-diagnostic-2.c, with the goal to improve the macro expansion output printed by GCC with -ftrack-macro-expansion as well as its interaction with on #pragma GCC diagnostic.  It seems to me that the change was ill thought out: I can think of no reason why -Wunitialized should be treated differently from all other warnings.

$ cat a.c && gcc -O2 -S -Wall -Werror a.c
#define X(i) f (a[i]);

int f (int);

int g (void)
{
  int a[3];
#pragma GCC diagnostic push
#pragma GCC diagnostic warning "-Wuninitialized"
  return X (1);
#pragma GCC diagnostic pop
}

int h (void)
{
  int a[] = { 1, 2, 3 };
#pragma GCC diagnostic push
#pragma GCC diagnostic warning "-Warray-bounds"
  return X (3);
#pragma GCC diagnostic pop
}
a.c: In function ‘g’:
a.c:1:14: error: ‘a’ is used uninitialized [-Werror=uninitialized]
    1 | #define X(i) f (a[i]);
      |              ^~~~~~~~
a.c:10:10: note: in expansion of macro ‘X’
   10 |   return X (1);
      |          ^
a.c:7:7: note: ‘a’ declared here
    7 |   int a[3];
      |       ^
a.c: In function ‘h’:
a.c:1:14: warning: array subscript 3 is above array bounds of ‘int[3]’ [-Warray-bounds]
    1 | #define X(i) f (a[i]);
      |              ^~~~~~~~
a.c:19:10: note: in expansion of macro ‘X’
   19 |   return X (3);
      |          ^
a.c:16:7: note: while referencing ‘a’
   16 |   int a[] = { 1, 2, 3 };
      |       ^
cc1: all warnings being treated as errors