I've looked at warnings I get in the Linux kernel with older compilers but not with more modern versions. Unsurprisingly, most are false positives, but I found three files that show a particular pattern that should be warned about:

$ gcc-8.0.0 -Wall -c test.c -O2 # no warning
$ gcc-8.0.0 -Wall -c test.c -O2 -fno-tree-vrp # warning
test.c:12:9: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
$ gcc-4.8 -Wall -c test2.c -O2 # warning
test.c:12:2: warning: ‘err’ may be used uninitialized in this function [-Wmaybe-uninitialized]

The original warnings all show up with gcc-4.6 and earlier, but not with gcc-4.7+. The reduced test case also produces a warning with 4.7 and 4.8 but not with 4.9 through 8.0 unless -ftree-vrp is disabled:

8<---
int f(void);
int mlx5_fpga_mem_read_i2c(int count)
{
	int i, err;

	for (i = 0; i < count; i++) {
		err = f();
		if (err)
			break;
	}

	return err;
}
----->8

There are a lot of similar reports that are all marked duplicates of pr18501, but none of them have the particular loop/break pattern that I found in the three kernel files, so I'm opening another one to be sure.

If the underlying problem is the same, please mark this one as duplicate as well.