[Mlir-commits] [mlir] [mlir][ArmSVE] Lower predicate-sized vector.create_masks to whilelt (PR #95531)

[Cullen Rhodes]

================
@@ -140,6 +140,40 @@ using ConvertFromSvboolOpLowering =
 using ZipX2OpLowering = OneToOneConvertToLLVMPattern<ZipX2Op, ZipX2IntrOp>;
 using ZipX4OpLowering = OneToOneConvertToLLVMPattern<ZipX4Op, ZipX4IntrOp>;
 
+/// Converts `vector.create_mask` ops that match the size of an SVE predicate
+/// to the `whilelt` intrinsic. This produces more canonical codegen than the
+/// generic LLVM lowering, see https://github.com/llvm/llvm-project/issues/81840
+/// for more details. Note that we can't (the more general) get.active.lane.mask
+/// as its semantics don't neatly map on to `vector.create_mask`, as it does an
+/// unsigned comparison (whereas `create_mask` is signed), and is UB/posion if
+/// `n` is zero (whereas `create_mask` just returns an all-false mask).
+struct PredicateCreateMaskOpLowering
----------------
c-rhodes wrote:

nit: drop "Predicate"?
```suggestion
struct CreateMaskOpLowering
```

https://github.com/llvm/llvm-project/pull/95531