[LLVMdev] Limit loop vectorizer to SSE

[Nadav Rotem]

On Nov 15, 2013, at 12:36 PM, Renato Golin <renato.golin at linaro.org> wrote:

> On 15 November 2013 20:24, Joshua Klontz <josh.klontz at gmail.com> wrote:
> Agreed, is there a pass that will insert a runtime alignment check? Also, what's the easiest way to get at TargetTransformInfo::getRegisterBitWidth() so I don't have to hard code 32? Thanks!
> 
> I think that's a fair question, and it's about safety. If you're getting this on the JIT, means we may be generating unsafe transformations on the vectorizer.
> 
> Arnold, Nadav, I don't remember seeing code to generate any run-time alignment checks on the incoming pointer, is there such a thing? If not, shouldn't we add one?



If the the vectorizer generates aligned memory accesses to unaligned addresses then this is a serious bug.  But I don’t think that Josh said that the vectorizer generated aligned accesses to unaligned pointers. 

There is no point in LLVM checking for alignment because if the memory is unaligned then the program will crash.  Users who want to crash with a readable error message can simply write code that checks the pointer (by masking the high bits and comparing to zero).  

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