[PATCH] D76528: [clang codegen] Clean up handling of vectors with trivial-auto-var-init.

[Eli Friedman via Phabricator via cfe-commits]

efriedma added a comment.

Not sure what sort of test would catch this; it's not crashing, and the types with the tail padding issue are not naturally exposed by target intrinsic headers (so it would only show up for code using ext_vector_type, or maybe OpenCL code).  I only tripped over the issue by inspection.

The way LLVM currently works, vectors never have internal padding, only tail padding.  (This could possibly change in the future, I guess, but there aren't any specific plans.)

For the types clang can generate, tail padding can show up a few different ways:

1. A vector can have an element count that's not a power of two: <5 x double>
2. A vector can partially cover a byte: <4 x i1>
3. A vector can have an element type that naturally has padding, like x86 long double

I can write testcases for the above, if you would find it helpful.  (Actually figuring out how to pad a vector correctly is more work than I really want to invest into this right now.  In the tricky cases, it might make sense to convert the constant to an integer, and pad that.)


Repository:
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https://reviews.llvm.org/D76528