[PATCH] [LoopVectorize]Teach Loop Vectorizer about interleaved memory access

[Adam Nemet]

In http://reviews.llvm.org/D9368#177506, @HaoLiu wrote:

> I think LoopAccessAnalysis is a specific analysis for LV, so it's reasonable to put interleaved access analysis in an analysis specific for LV. If LoopAccessAnalysis is not specific for LV, I agree that we should not put it here. Currently I don't have idea about how other clients could use such interleave information.
>
> But I still wonder how "other" clients use this analysis, as it has a lot of LV specific code like "CanVecMem, force-vector-width, force-vector-interleave", .... I wonder how "other" clients could use such analysis. Adam, do you have any example about other clients using LoopAccessAnalysis?


Sure, I already mentioned both clients: Transforms/Scalar/LoopDistribute.cpp and the still pending Ashutosh's Loop versioning pass in http://reviews.llvm.org/D9151.

Regarding your first specific question on CanVecMem, the basic design principle for splitting out LAA fron LV was to continue to provide the high-level LV-specific answers (i.e. CanVecMem) but also provide more lower-level/generic information about the dependences and run-time checks so that other passes could also use them (see APIs like: getInterestingDependences, getMemoryInstructions, getRuntimeChecks and getInstructionsForAccess).

Your other question was about force-vector-width, etc.  These influence what dependences are acceptable for LV for its specific view of the dependence information.   The solution here was to provide subtypes like *Vectorizable (see Dependence::DepType).  These "subtypes" provide further classification of the dependence.  LV uses these to allow vectorization of certain Backward dependences.

Loop Distribution does not use this classification since it only cares about forward vs. backward dependences.

Thus the difference is exposed to the clients and they can chose to treat these types differently or uniformly.

Adam


http://reviews.llvm.org/D9368

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