[mlir] stopgap for incorrect vector.contract lowering

[ftynse]

Summary

vector.contract is being lowered to the default mul/add contraction
regardless if of the kind indicated. Stop the lowering completely in
this case until the correct one can be implemented.

[ThomasRaoux]

Thanks Alex

mlir/lib/Dialect/Vector/Transforms/VectorTransforms.cpp

if (failed(filter(op)))
     return failure();
 
   // TODO: support mixed mode contract lowering.
   if (op.getLhsType().getElementType() !=
           getElementTypeOrSelf(op.getAccType()) ||
       op.getRhsType().getElementType() != getElementTypeOrSelf(op.getAccType()))
     return failure();
 
+  // TODO: the code below assumes the default contraction, make sure it supports
+  // other kinds before enabling this lowering.
+  if (op.getKind() != vector::CombiningKind::ADD) {
+    return rewriter.notifyMatchFailure(
+        op, "contractions other than 'add' not supported");
+  }
+
   // TODO: implement benefits, cost models.
   MLIRContext *ctx = op.getContext();
   ContractionOpToMatmulOpLowering pat1(vectorTransformOptions, ctx);
   if (succeeded(pat1.matchAndRewrite(op, rewriter)))
     return success();
   ContractionOpToOuterProductOpLowering pat2(vectorTransformOptions, ctx);
   if (succeeded(pat2.matchAndRewrite(op, rewriter)))
     return success();