[NFC] Add comment explaining unused vectorSizes/scalableDims in im2col

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Max Dawkins <max.dawkins@gmail.com>

Author: Max191

compiler/src/iree/compiler/Codegen/Interfaces/VectorizableOpInterface.cpp

@@ -1149,10 +1149,12 @@ static Value computeIm2colPaddingMask(
   return vector::CreateMaskOp::create(b, loc, vecI1Type, validSize);
 }
 
+// Im2col vectorization computes its own vector width via
+// chooseDimToVectorize() based on the op's layout and contiguity
+// constraints, rather than using the driver-provided vectorSizes.
 struct Im2colOpVectorizationModel
     : public VectorizableOpInterface::ExternalModel<Im2colOpVectorizationModel,
                                                     IREE::LinalgExt::Im2colOp> {
-
   bool isVectorizable(Operation *op, ArrayRef<int64_t> vectorSizes,
                       ArrayRef<bool> scalableDims,
                       DictionaryAttr options) const {