Crash in SmallVector with latest MSVC 2019 (debug mode)

Is anybody using the LLVM/clang/lldb compiled with the MSVC 2019 (x86-32bit) successfully?
I am getting crash in SmallVector at multiple places after a llvm:SmallVector is being moved around in move constructor or move operator=.
Not sure what is going on.

~SmallVectorImpl() {
if (!this->isSmall())
free(this->begin()); // <=== crash here, line 336 SmallVector.h
}

The crash occurs only with clang compile in debug mode. Release mode is fine.

The crash occurs only with clang compile in debug mode.

Sanity check: you’re not mixing clang in debug mode with LLVM in release mode, right?
I’ve seen similar crashes in DenseMap when I accidentally did the above.

I don’t think there is anymore upstream LLVM testing for 32-bit MSVC. I’ll run a local build in this configuration and look into it. I’ll use this compiler version:
Microsoft (R) C/C++ Optimizing Compiler Version 19.24.28315 for x86

We had so many issues in clang-cl around calling conventions for “small” objects with interior pointers, I wouldn’t be surprised if there are bugs.

I was able to reproduce the problem. It seems to relate to the use of a UniqueVector (which uses std::vector internally) of SmallVectors here:
https://github.com/llvm/llvm-project/blob/master/llvm/utils/TableGen/DFAEmitter.h#L91

Aside from potential MSVC bugs, this is a poor choice of data structures. I would suggest using a SmallVector<T, 0> or std::vector instead. So, we could commit that as a workaround.

Relatedly, debug MSVC tablegen builds are still unusably slow. :frowning:
https://bugs.llvm.org/show_bug.cgi?id=28222

Thank you.

Yes the bug occurs in tablegen first but even if you bypass tablegen-debug it will eventually occur elsewhere too (llvm, lldb etc)…

I’ll try to reduce the problem in a isolated test case and submit a bug to Microsoft.
Sadly I am stuck with 32-bit compile for now because we use liblldb.dll and libclang.dll as in-process DLL inside a 32-bit .exe.

(Forgot reply-all)