This allows the lowering of > rank 1 transfer_reads/writes to equivalent
lower-rank ones when the trailing dimension is scalable. The resulting
ops still cannot be completely lowered as they depend on arrays of
scalable vectors being enabled, and a few related fixes (see D158517).
This patch also explicitly disables lowering transfer_reads/writes with
a leading scalable dimension, as more changes would be needed to handle
that correctly and it is unclear if it is required.
Examples of ops that can now be further lowered:
%vec = vector.transfer_read %arg0[%c0, %c0], %cst, %mask
{in_bounds = [true, true]} : memref<3x?xf32>, vector<3x[4]xf32>
vector.transfer_write %vec, %arg0[%c0, %c0], %mask
{in_bounds = [true, true]} : vector<3x[4]xf32>, memref<3x?xf32>
Reviewed By: c-rhodes, awarzynski, dcaballe
Differential Revision: https://reviews.llvm.org/D158753
2a82dfd704