ilinpv added a comment.
In D127812#4012283 <https://reviews.llvm.org/D127812#4012283>, @hctim wrote:
> I'm not sure "MSan didn't handle correctly SmallVector" is the case. Given
> your diagnosis of 3-elements-vs-2, I'm guessing the root cause is that
> `clang/lib/Sema/SemaDecl.cpp:11369` is wrong:
>
> !std::equal(CurClones->featuresStrs_begin(),
> CurClones->featuresStrs_end(),
> NewClones->featuresStrs_begin()))) {
>
> This construction of `std::equal` is very error-prone, as if
> `NewClones.size() < CurClones.size()`, then this invariable leads to
> buffer-overflow. I'm wondering if that's the underlying cause, it would seem
> entirely possible that expanding the in-place elements are always
> "initialized" from MSan's perspective and so the current code has a
> false-negative, and your new code made it so that the vector is now
> heap-based, which is revealing the underlying issue. Maybe worth trying one
> more thing and adding an `assert(CurClones->size() <= NewClones->size());` to
> double check?
I don't think `std::equal` is underlying cause here. We have
featuresStrs_size() comparison before calling it:
if (CurClones && NewClones &&
(CurClones->featuresStrs_size() != NewClones->featuresStrs_size() ||
!std::equal(CurClones->featuresStrs_begin(),
CurClones->featuresStrs_end(),
NewClones->featuresStrs_begin()))) {
Also even if we completely remove std::equal the use-of-uninitialized-value
error still persist.
Repository:
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