This brings back previous SIMD functionality, but in a separate pass.
The idea is to improve this new pass incrementally, going beyond for-loops
to while-loops for co-iteration as welll (masking), while introducing new
abstractions to make the lowering more progressive. The separation of
sparsification and vectorization is a very good first step on this journey.
Also brings back ArmSVE support
Still to be fine-tuned:
+ use of "index" in SIMD loop (viz. a[i] = i)
+ check that all ops really have SIMD support
+ check all forms of reductions
+ chain reduction SIMD values
Reviewed By: dcaballe
Differential Revision: https://reviews.llvm.org/D138236
99b3849d89