[Bugfix] Guard mxfp4_experts_quant bindings on ENABLE_NVFP4_SM100 (#40191)

Signed-off-by: ultranationalism <www913363043@gmail.com>
Signed-off-by: mgoin <mike.goin12@gmail.com>
Co-authored-by: mgoin <mike.goin12@gmail.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

csrc/libtorch_stable/ops.h

@@ -134,20 +134,6 @@ void silu_and_mul_nvfp4_quant(torch::stable::Tensor& out,
                               torch::stable::Tensor& input,
                               torch::stable::Tensor& input_global_scale);
 
-void mxfp4_experts_quant(
-    torch::stable::Tensor& output, torch::stable::Tensor& output_scale,
-    torch::stable::Tensor const& input,
-    torch::stable::Tensor const& input_offset_by_experts,
-    torch::stable::Tensor const& output_scale_offset_by_experts,
-    int64_t n_experts);
-
-void silu_and_mul_mxfp4_experts_quant(
-    torch::stable::Tensor& output, torch::stable::Tensor& output_scale,
-    torch::stable::Tensor const& input,
-    torch::stable::Tensor const& input_offset_by_experts,
-    torch::stable::Tensor const& output_scale_offset_by_experts,
-    int64_t n_experts);
-
 void cutlass_mxfp4_group_mm(torch::stable::Tensor& output,
                             const torch::stable::Tensor& a,
                             const torch::stable::Tensor& b,

csrc/libtorch_stable/quantization/fp4/mxfp4_experts_quant.cu

@@ -23,6 +23,7 @@
 #include <cuda_runtime.h>
 #include <cuda_fp8.h>
 
+#include <torch/csrc/stable/library.h>
 #include <torch/csrc/stable/tensor.h>
 #include "libtorch_stable/torch_utils.h"
 #include "libtorch_stable/dispatch_utils.h"
@@ -420,3 +421,12 @@ void silu_and_mul_mxfp4_experts_quant(
             stream);
       });
 }
+
+// Registered here (not torch_bindings.cpp) because VLLM_GPU_FLAGS is applied
+// only under COMPILE_LANGUAGE:CUDA, so ENABLE_NVFP4_SM100 is invisible to
+// .cpp files and cannot gate the registration from there.
+STABLE_TORCH_LIBRARY_IMPL(_C, CUDA, m) {
+  m.impl("mxfp4_experts_quant", TORCH_BOX(&mxfp4_experts_quant));
+  m.impl("silu_and_mul_mxfp4_experts_quant",
+         TORCH_BOX(&silu_and_mul_mxfp4_experts_quant));
+}

csrc/libtorch_stable/torch_bindings.cpp

@@ -252,12 +252,8 @@ STABLE_TORCH_LIBRARY_IMPL(_C, CUDA, ops) {
   ops.impl("silu_and_mul_scaled_fp4_experts_quant",
            TORCH_BOX(&silu_and_mul_scaled_fp4_experts_quant));
   ops.impl("silu_and_mul_nvfp4_quant", TORCH_BOX(&silu_and_mul_nvfp4_quant));
-  ops.impl("mxfp4_experts_quant", TORCH_BOX(&mxfp4_experts_quant));
-  ops.impl("silu_and_mul_mxfp4_experts_quant",
-           TORCH_BOX(&silu_and_mul_mxfp4_experts_quant));
-
-  // W4A8 ops: impl registrations are in the source files
-  // (w4a8_mm_entry.cu and w4a8_grouped_mm_entry.cu)
+  // mxfp4_experts_quant: registered in mxfp4_experts_quant.cu (SM100 only).
+  // W4A8 ops: registered in w4a8_mm_entry.cu / w4a8_grouped_mm_entry.cu.
 #endif
 }