This is a continuation of my patches to inform the X86 backend about what the largest IR types are in the function so that we can restrict the backend type legalizer to prevent 512-bit vectors on SKX when -mprefer-vector-width=256 is specified if no explicit 512 bit vectors were specified by the user.
This patch updates the vector width based on the argument and return types of the current function and from the types of any functions it calls. This is intended to make sure the backend type legalizer doesn't disturb any types that are required for ABI.
These attribute changes don't appear to test anything. They don't say anything about the min-legal-vector-width. It's unfortunate that LLVM attribute syntax is so filecheck unfriendly, but for now, I think you need to check for #0, #1, etc attribute definitions at the end of each .c file.