mstorsjo added a comment.
In D105169#3069220 <https://reviews.llvm.org/D105169#3069220>, @aqjune wrote:
> It seems the original code has a use of an uninitialized variable.
> Line 4420 at seek-preproc.c (function `ff_seek_frame_binary`):
>
> int64_t pos_min=pos_min, pos_max=pos_max, pos, pos_limit; // pos_min and
> pos_max are self-assigned.
> ...
> if (sti->index_entries) {
> ...
> }
> // pos_min and pos_max are used as arguments below
> pos = ff_gen_search(s, stream_index, target_ts, pos_min, pos_max, pos_limit,
> ts_min, ts_max, flags, &ts, avif->read_timestamp);
>
> https://gist.github.com/aqjune/3bd0ea19bbc12b4744843c0c070e994c
>
> If the branch is not taken, `pos_min` and `pos_max` are read while they are
> still uninitialized.
>
> I guess the variables are self-assigned to avoid warnings?
Yes, I believe so. If the branch is not taken, `pos_min` and `pos_max` are
undefined when entering `ff_gen_search`. (I would assume that their value isn't
ever used within `ff_gen_search` in that case.) But regardless of that, in this
case, the generated code crashes around this line,
https://gist.github.com/aqjune/3bd0ea19bbc12b4744843c0c070e994c#file-ff_seek_frame_binary-c-L39,
before entering `ff_gen_search` - and within that branch, those variables are
properly set before they're used.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D105169/new/
https://reviews.llvm.org/D105169
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