[Mosaic] Pad trailing transposes chunks with zeros.

PiperOrigin-RevId: 705310340

Author: WindQAQ

jaxlib/mosaic/dialect/tpu/transforms/apply_vector_layout.cc

@@ -4623,7 +4623,9 @@ LogicalResult vector_transpose_rule(RewriteContext &ctx, Operation &op,
                           incremented_batch_idx.end());
     src_slice_ends.append({(src_row + 1) * vregs_per_tile, src_col_end});
     xla::Array<Value> src_tile_vregs = src_vregs.Slice(
-        src_slice_starts, src_slice_ends, /*out_of_bounds_ok=*/true);
+        src_slice_starts, src_slice_ends,
+        builder.create<arith::ConstantOp>(
+            op.getLoc(), builder.getZeroAttr(src_vregs.begin()->getType())));
     // Drop leading singleton (batch) dimensions to have a shape that conforms
     // with the vreg array shape specified by layout_in, as expected by assemble
     src_tile_vregs.Reshape(