FailedChanges

Summary

  1. Use pragmas to work around MSVC x86_32 debug miscompile bug (details)
Commit 4e3edef4b8b637c0c76897497eb7c66f00157210 by rnk
Use pragmas to work around MSVC x86_32 debug miscompile bug

Halide users reported this here: https://llvm.org/pr46176
I reported the issue to MSVC here:
https://developercommunity.visualstudio.com/content/problem/1179643/msvc-copies-overaligned-non-trivially-copyable-par.html

This codepath is apparently not covered by LLVM's unit tests, so I added
coverage in a unit test.

If we want to support this configuration going forward, it means that is
in general not safe to pass a SmallVector<T, N> by value if alignof(T)
is greater than 4. This doesn't appear to come up often because passing
a SmallVector by value is inefficient and not idiomatic: it copies the
inline storage. In this case, the SmallVector<LLT,4> is captured by
value by a lambda, and the lambda is passed by value into std::function,
and that's how we hit the bug.

Differential Revision: https://reviews.llvm.org/D87475
The file was modifiedllvm/lib/CodeGen/GlobalISel/LegalityPredicates.cpp (diff)
The file was modifiedllvm/unittests/CodeGen/GlobalISel/LegalizerInfoTest.cpp (diff)