Bug 276224 – [GStreamer] gstStructureGet<T> may return optionals with unitialized values on Clang 18

• Status: RESOLVED
• Resolution: FIXED
• Component: Platform

[Carlos Bentzen]

On bug 275609 we introduced the gstStructureGet<T> helper. After using it in more places, we found what may be a compiler bug (reproduced it with Clang 18 so far).

Given a GstStructure named structure with "a-structure, width=10". If we try:

auto height = gstStructureGet<int>(structure, "height"_s);
if (height)
    GST_LOG("height = %d", *height);

although the branch shouldn't be executed since there's no "height" field. It is executed with an unitialized value.

After debugging what's happening, it seems to be actually a compiler issue. Fixed it by using if(UNLIKELY(gst_structure_get_<type>)) in gstStructureGet branches. Without that, the branches were being executed and returning std::optional with unitialized values when they shouldn't.

Patch for the fix in WebKit incoming. Pending on a minimal reproducer outside WebKit to confirm it's a bug in Clang...

[Philippe Normand]

*** Bug 276222 has been marked as a duplicate of this bug. ***

[Carlos Bentzen]

Reduced the copmpiler bug outside of WebKit at https://github.com/cadubentzen/std-optional-bug-clang

[Carlos Bentzen]

Pull request: https://github.com/WebKit/WebKit/pull/30493

[EWS]

Committed 280669@main (98b041523464): <https://commits.webkit.org/280669@main>

Reviewed commits have been landed. Closing PR #30493 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/131130985>