[PATCH] [X86] Replace (v)palignr intrinsics with generic shuffles (Clang)

[Simon Pilgrim]

In http://reviews.llvm.org/D8301#140042, @craig.topper wrote:

> We've always been sending shuffles to the backend. We just generated the shuffles in CGBuiltin instead of the header.


Hi Craig, yes, I was hoping that this patch would get us to the point that we could get rid of even that - or is the CGBuiltin stage good enough do you think?

> I'm not sure I like completely losing the type system on the immediate. Theoretically with the code in CGBuiltin we could at least get a truncation warning if the immediate was larger than a byte. Though I'm not sure that warning is on by default. Really I wish we could check the immediates for illegal values on all of these macros and deliver nice messages to the user. I think gcc does check a lot of them.


Short of adding static_assert I'm not sure of the best way of doing this. We're in a position at the moment of having some of the intrinsics already converted over to pure __builtin_shufflevector implementations despite having a similar problem - the slldq/srldq byte shifts come to mind which are pretty similar to alignr.


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