[kernel] Support W4A8 on Hopper (#23198)

Signed-off-by: czhu-cohere <conway.zhu@cohere.com>

csrc/torch_bindings.cpp

@@ -309,6 +309,26 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
       "awq_marlin_repack(Tensor b_q_weight, SymInt size_k, "
       "SymInt size_n, int num_bits) -> Tensor");
   // conditionally compiled so impl registrations are in source file
+
+  // CUTLASS w4a8 GEMM
+  ops.def(
+      "cutlass_w4a8_mm("
+      "   Tensor A,"
+      "   Tensor B,"
+      "   Tensor group_scales,"
+      "   int    group_size,"
+      "   Tensor channel_scales,"
+      "   Tensor token_scales,"
+      "   ScalarType? out_type,"
+      "   str?   maybe_schedule"
+      ") -> Tensor",
+      {stride_tag});
+  // pack scales
+  ops.def("cutlass_pack_scale_fp8(Tensor scales) -> Tensor");
+  // encode and reorder weight matrix
+  ops.def("cutlass_encode_and_reorder_int4b(Tensor B) -> Tensor");
+  // conditionally compiled so impl registration is in source file
+
 #endif
 
   // Dequantization for GGML.