[Bug tree-optimization/100115] Bogus -Wmaybe-uninitialized warning with -O3
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100115 --- Comment #3 from Martin Sebor --- The reason why the warning tends to disappear in a simpler test case is because of the limit (I just had it happen with my reduction). Don't spend more time on it than you already have, I'll work with the attached translation unit. The warning is exquisitely sensitive to optimizations so when GCC doesn't optimize something in a way that lets it prove the uninitialized read is impossible, it triggers. I'm hoping to improve this for GCC 12.
[Bug tree-optimization/100115] Bogus -Wmaybe-uninitialized warning with -O3
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100115 --- Comment #2 from Boris Kolpackov --- > I'm trying to reduce the test case to something manageable but that can take > many hours, even days. Right. On our side we have spent hours, even days trying to suppress this warning (both by rearranging the code and with #pragma) but it keep popping up in different places and on different targets (MinGW, Mac OS, etc). In fact, we've wasted so much time on chasing this (and similar issues in the past), that I am seriously considering just globally disabling this warning since it seems more trouble than it's worth. Sorry, just venting a bit here... > It would be really helpful if you could trim it down a bit, e.g., by removing > the biggest non-essentials like . I will try. The thing is, such simplifications often make the warning disappear. We have tens of similar code fragments in our codebase, but only this one triggers a warning on x86_64-linux (other places trigger it on MinGW and Mac OS). > That being said, the context of the warning mentions std::optional which has > been known to be challenging for analysis [...] Yes, I can confirm that most of the issues with this warning we've encountered in the past involved std::optional.
[Bug tree-optimization/100115] Bogus -Wmaybe-uninitialized warning with -O3
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100115 Martin Sebor changed: What|Removed |Added Component|c++ |tree-optimization CC||msebor at gcc dot gnu.org Keywords||diagnostic Blocks||24639 --- Comment #1 from Martin Sebor --- I can confirm the warning but the test case is far too big for me to say whether or not it's valid. As it turns out, the test case is also too big for GCC as it exceeds at least one internal limit named MAX_CHAIN_LEN. The limit is hardcoded to an exceedingly low value of 5 but with the test case reaches 77. Exceeding this limit can lead to either false positives or negatives. But bumping it way up doesn't avoid the warning so something else is going on. I'm trying to reduce the test case to something manageable but that can take many hours, even days. It would be really helpful if you could trim it down a bit, e.g., by removing the biggest non-essentials like . That being said, the context of the warning mentions std::optional which has been known to be challenging for analysis and has led to false positives (see pr80635 and related) as well as less than optimal code in the past, so I expect this is going to caused by a similar limitation. Referenced Bugs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639 [Bug 24639] [meta-bug] bug to track all Wuninitialized issues
