[PATCH] D99790: [CGCall] Annotate `this` argument with alignment

[James Y Knight via Phabricator via llvm-commits]

jyknight added a comment.

In D99790#2677917 <https://reviews.llvm.org/D99790#2677917>, @brooksmoses wrote:

> As a heads up, I'm seeing segfaults on internal code as a result of this change, as well as errors in Eigen's unalignedassert.cpp test (specifically, this line asserts: https://github.com/madlib/eigen/blob/master/test/unalignedassert.cpp#L151).

Eigen's case is UB -- the test case is verifying that the constructor of the Matrix type throws an exception if called on an under-aligned instance, I think in an effort to make the UB noisier for their users. It already didn't work in GCC, and they had a "workaround", here, https://github.com/madlib/eigen/blob/fa14b05455c9d9737ae577f686188ef358df9020/Eigen/src/Core/DenseStorage.h#L63

It's unsurprising that this change in Clang causes the same code to fail in Clang, too.


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