[mlir] [VectorOps] Add missing comments to CreateMaskOp lowering

[aartbik]

Summary

Add missing comment to CreateMask. Fixed typo in ConstantMask comment.

[ftynse]

Thanks!

mlir/lib/Dialect/Vector/VectorTransforms.cpp

LogicalResult matchAndRewrite(vector::OuterProductOp op,
     }
     rewriter.replaceOp(op, result);
     return success();
   }
 };
 
 /// Progressive lowering of ConstantMaskOp.
 /// One:
-///   %x = vector.constant_mask_op [a,b]
+///   %x = vector.constant_mask [a,b]
 /// is replaced by:
 ///   %z = zero-result
-///   %l = vector.constant_mask_op [b]
+///   %l = vector.constant_mask [b]
 ///   %4 = vector.insert %l, %z[0]
 ///   ..
 ///   %x = vector.insert %l, %..[a-1]
 /// which will be folded at LLVM IR level.
 class ConstantMaskOpLowering : public OpRewritePattern<vector::ConstantMaskOp> {
 public:
   using OpRewritePattern<vector::ConstantMaskOp>::OpRewritePattern;
 
for (int64_t d = 0; d < trueDim; d++) {
       result =
           rewriter.create<vector::InsertOp>(loc, dstType, trueVal, result, pos);
     }
     rewriter.replaceOp(op, result);
     return success();
   }
 };
 
+/// Progressive lowering of CreateMaskOp.
+/// One:
+///   %x = vector.create_mask %a, ... : vector<dx...>
+/// is replaced by:
+///   %l = vector.create_mask ... : vector<...>  ; one lower rank
+///   %0 = cmpi "slt", %ci, %a       |
+///   %1 = select %0, %l, %zeroes    |
+///   %r = vector.insert %1, %pr [i] | d-times
+///   %x = ....
+/// When rank == 1, the selection operator is not needed,
+/// and we can assign the true/false value right away.
 class CreateMaskOpLowering : public OpRewritePattern<vector::CreateMaskOp> {
 public:
   using OpRewritePattern<vector::CreateMaskOp>::OpRewritePattern;
 
   LogicalResult matchAndRewrite(vector::CreateMaskOp op,
                                 PatternRewriter &rewriter) const override {
     auto loc = op.getLoc();
     auto dstType = op.getResult().getType().cast<VectorType>();