Variables used uninitialized in libavformat/utils.c

[Jeremy Huddleston]

The following were observed when building N-77414-g484cc66 and should probably be fixed:

libavformat/utils.c:1896:9: warning: variable 'pos_min' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
    if (st->index_entries) {
        ^~~~~~~~~~~~~~~~~
libavformat/utils.c:1929:53: note: uninitialized use occurs here
    pos = ff_gen_search(s, stream_index, target_ts, pos_min, pos_max, pos_limit,
                                                    ^~~~~~~
libavformat/utils.c:1896:5: note: remove the 'if' if its condition is always true
    if (st->index_entries) {
    ^~~~~~~~~~~~~~~~~~~~~~~
libavformat/utils.c:1880:5: note: variable 'pos_min' is declared here
    int64_t av_uninit(pos_min), av_uninit(pos_max), pos, pos_limit;
    ^
libavformat/utils.c:1918:13: warning: variable 'pos_max' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (index >= 0) {
            ^~~~~~~~~~
libavformat/utils.c:1929:62: note: uninitialized use occurs here
    pos = ff_gen_search(s, stream_index, target_ts, pos_min, pos_max, pos_limit,
                                                             ^~~~~~~
libavformat/utils.c:1918:9: note: remove the 'if' if its condition is always true
        if (index >= 0) {
        ^~~~~~~~~~~~~~~~
libavformat/utils.c:1896:9: warning: variable 'pos_max' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
    if (st->index_entries) {
        ^~~~~~~~~~~~~~~~~
libavformat/utils.c:1929:62: note: uninitialized use occurs here
    pos = ff_gen_search(s, stream_index, target_ts, pos_min, pos_max, pos_limit,
                                                             ^~~~~~~
libavformat/utils.c:1896:5: note: remove the 'if' if its condition is always true
    if (st->index_entries) {
    ^~~~~~~~~~~~~~~~~~~~~~~
libavformat/utils.c:1880:5: note: variable 'pos_max' is declared here
    int64_t av_uninit(pos_min), av_uninit(pos_max), pos, pos_limit;
    ^
3 warnings generated.

[Carl Eugen Hoyos]

Both variables are not accessed if they are uninitialized and the compiler should be able to see this. Maybe the standard forbids to pass uninitialized values as function parameters?

[Elon Musk]

They are accessed if they are uninitialized.

[Elon Musk]

They are accessed if they are uninitialized.

[Hendrik]

The compiler seems to complain about passing an uninitialized variable to another function, but not actually checking if that function uses it under the given conditions.

Last I checked this code, it did not actually use these variables uninitialized, however the design might not be very easy to understand since it spans more then one function, and these variables are passed as arguments in between.

[Carl Eugen Hoyos]

Isn't the question if the standard allows to pass uninitialized parameters?