[PATCH] D31885: Remove TBAA information from LValues representing union members

[Hal Finkel via Phabricator via cfe-commits]

hfinkel added a comment.

In https://reviews.llvm.org/D31885#730853, @hfinkel wrote:

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>> (And the nonsensicality of the standard very much continues. The code that we've all agreed is obviously being miscompiled here is still a strict violation of the "improved" union rules in C++, and if we decide to treat it as ill-formed we're going to break a massive amount of code (and vector code in particular heavily uses unions), because trust me, nobody is reliably placement-newing union fields when they're non-trivial. C++'s new rules are unworkable in part because they rely on C++-specific features that cannot be easily adopted in headers which need to be language-neutral.)
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> I think we all agree that the vector types need to have their scalar (element) types as parents in the current TBAA representation. That's a separate change that we should just make. That, unfortunately, only fixes a subset of the union-related miscompiles.

Looking at this in more detail, we actually generate builtin-vector types which use char* as their access type (always, even for floating-point vectors). It is only the struct-path info which causes the issue for the test case here. It might be reasonable to make this **less** conservative, but that's another story...


Repository:
  rL LLVM

https://reviews.llvm.org/D31885