[torch.compile] Undo the fast_moe_cold_start hack in torch>=2.11 (#35475)

Signed-off-by: Richard Zou <zou3519@gmail.com>

vllm/config/vllm.py

@@ -883,7 +883,13 @@ class VllmConfig:
                     self.compilation_config.pass_config.enable_sp = False
                     self.compilation_config.pass_config.fuse_gemm_comms = False
 
-        if self.compilation_config.fast_moe_cold_start is None:
+        from vllm.utils.torch_utils import HAS_OPAQUE_TYPE
+
+        if HAS_OPAQUE_TYPE:
+            # On torch >= 2.11 the hoisted OpaqueObject approach supersedes
+            # fast_moe_cold_start, so force it off.
+            self.compilation_config.fast_moe_cold_start = False
+        elif self.compilation_config.fast_moe_cold_start is None:
             # resolve default behavior: try to be as safe as possible
             # this config is unsafe if any spec decoding draft model has a MOE.
             # We'll conservatively turn it off if we see spec decoding.

vllm/env_override.py

@@ -482,3 +482,44 @@ if is_torch_equal("2.9.0"):
 
     PythonWrapperCodegen.memory_plan_reuse = memory_plan_reuse_patched
     GraphLowering._update_scheduler = _update_scheduler_patched
+
+# ===================================================
+# torch 2.11 Inductor constrain_to_fx_strides monkeypatch
+# ===================================================
+# Patch the inductor's `constrain_to_fx_strides` to handle opaque
+# (non-tensor) arguments.  The original calls `.stride()` on every FX
+# arg's meta value, which crashes on FakeScriptObject (the compile-time
+# proxy for hoisted opaque types).  The patched version skips args
+# whose meta value is not a torch.Tensor.
+# Upstream issue: https://github.com/pytorch/pytorch/issues/175973
+
+from vllm.utils.torch_utils import is_torch_equal_or_newer
+
+if is_torch_equal_or_newer("2.11.0.dev"):
+    import torch._inductor.ir as _ir
+    import torch._inductor.lowering as _lowering
+    from torch._inductor.virtualized import V as _V
+
+    _orig_constrain = _lowering.constrain_to_fx_strides
+
+    def _patched_constrain_to_fx_strides(fx_node, *args, **kwargs):
+        def apply_constraint(arg, fx_arg):
+            if isinstance(arg, _ir.IRNode):
+                meta_val = fx_arg.meta.get("val")
+                if isinstance(meta_val, torch.Tensor):
+                    stride_order = _ir.get_stride_order(
+                        meta_val.stride(), _V.graph.sizevars.shape_env
+                    )
+                    return _ir.ExternKernel.require_stride_order(arg, stride_order)
+                return arg
+            if isinstance(arg, dict):
+                return {key: apply_constraint(arg[key], fx_arg[key]) for key in arg}
+            return arg
+
+        args = tuple(
+            apply_constraint(arg, fx_arg) for arg, fx_arg in zip(args, fx_node.args)
+        )
+        kwargs = {k: apply_constraint(v, fx_node.kwargs[k]) for k, v in kwargs.items()}
+        return args, kwargs
+
+    _lowering.constrain_to_fx_strides = _patched_constrain_to_fx_strides

vllm/model_executor/layers/fused_moe/runner/default_moe_runner.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 from contextlib import nullcontext
+from typing import TYPE_CHECKING
 
 import torch
 import torch.nn.functional as F
@@ -30,6 +31,8 @@ from vllm.model_executor.layers.fused_moe.runner.moe_runner import MoERunner
 from vllm.platforms import current_platform
 from vllm.utils.math_utils import cdiv
 from vllm.utils.torch_utils import (
+    HAS_OPAQUE_TYPE,
+    ModuleName,
     aux_stream,
     current_stream,
     direct_register_custom_op,
@@ -56,13 +59,27 @@ def get_layer_from_name(layer_name: str) -> torch.nn.Module:
     return forward_context.no_compile_layers[layer_name]
 
 
+# On torch >= 2.11, layer_name is a hoisted ModuleName opaque object;
+# on older versions it remains a plain str.
+if TYPE_CHECKING:
+    from typing import TypeAlias
+
+    _layer_name_type: TypeAlias = str | ModuleName
+else:
+    _layer_name_type = ModuleName if HAS_OPAQUE_TYPE else str
+
+
+def _resolve_layer_name(layer_name: str | ModuleName) -> str:
+    return layer_name.value if isinstance(layer_name, ModuleName) else layer_name
+
+
 def _moe_forward(
     hidden_states: torch.Tensor,
     router_logits: torch.Tensor,
     shared_experts_input: torch.Tensor | None,
-    layer_name: str,
+    layer_name: _layer_name_type,
 ) -> torch.Tensor:
-    layer = get_layer_from_name(layer_name)
+    layer = get_layer_from_name(_resolve_layer_name(layer_name))
     # TODO(bnell): this can be removed after MK migration is complete.
     layer.ensure_moe_quant_config_init()
     return layer.runner.forward_impl(
@@ -74,7 +91,7 @@ def _moe_forward_fake(
     hidden_states: torch.Tensor,
     router_logits: torch.Tensor,
     shared_experts_input: torch.Tensor | None,
-    layer_name: str,
+    layer_name: _layer_name_type,
 ) -> torch.Tensor:
     return torch.empty_like(hidden_states)
 
@@ -83,9 +100,9 @@ def _moe_forward_shared(
     hidden_states: torch.Tensor,
     router_logits: torch.Tensor,
     shared_experts_input: torch.Tensor | None,
-    layer_name: str,
+    layer_name: _layer_name_type,
 ) -> tuple[torch.Tensor, torch.Tensor]:
-    layer = get_layer_from_name(layer_name)
+    layer = get_layer_from_name(_resolve_layer_name(layer_name))
     # TODO(bnell): this can be removed after MK migration is complete.
     layer.ensure_moe_quant_config_init()
     return layer.runner.forward_impl(
@@ -97,7 +114,7 @@ def _moe_forward_shared_fake(
     hidden_states: torch.Tensor,
     router_logits: torch.Tensor,
     shared_experts_input: torch.Tensor | None,
-    layer_name: str,
+    layer_name: _layer_name_type,
 ) -> tuple[torch.Tensor, torch.Tensor]:
     # Output shapes:
     # - fused_out: same as hidden_states (routed experts use transformed size)
@@ -105,12 +122,10 @@ def _moe_forward_shared_fake(
     #               hidden_states
     # (For latent MoE: shared experts use original hidden_size, not latent size)
     fused_out = torch.empty_like(hidden_states)
-
     if shared_experts_input is not None:
         shared_out = torch.empty_like(shared_experts_input)
     else:
         shared_out = torch.empty_like(hidden_states)
-
     return shared_out, fused_out
 
 
@@ -367,7 +382,9 @@ class DefaultMoERunner(MoERunner):
             assert len(trunc_sizes) == 1
             return func(states, trunc_sizes[0])
 
-    def _encode_layer_name(self) -> str:
+    def _encode_layer_name(self) -> str | ModuleName:
+        if HAS_OPAQUE_TYPE:
+            return ModuleName(self.layer_name)
         # Can be unavailable or None in unittests
         if (
             is_forward_context_available()

vllm/utils/torch_utils.py

@@ -740,6 +740,41 @@ def is_torch_equal(target: str) -> bool:
         return Version(importlib.metadata.version("torch")) == Version(target)
 
 
+HAS_OPAQUE_TYPE = is_torch_equal_or_newer("2.11.0.dev")
+
+if HAS_OPAQUE_TYPE:
+    from torch._opaque_base import OpaqueBase
+else:
+    OpaqueBase = object  # type: ignore[misc, assignment]
+
+
+class ModuleName(OpaqueBase):  # type: ignore[misc]
+    """Wraps a module name string for use as a torch opaque type.
+
+    When torch >= 2.11, this is registered as a hoisted value-type opaque
+    object so that torch.compile lifts it as a graph input instead of baking
+    it as a constant.  This avoids per-layer recompilation for MOE ops.
+    """
+
+    def __init__(self, value: str):
+        self.value = value
+
+    def __eq__(self, other):
+        return isinstance(other, ModuleName) and self.value == other.value
+
+    def __hash__(self):
+        return hash(self.value)
+
+    def __fx_repr__(self):
+        return (f"ModuleName({self.value!r})", {ModuleName})
+
+
+if HAS_OPAQUE_TYPE:
+    from torch._library.opaque_object import register_opaque_type
+
+    register_opaque_type(ModuleName, typ="value", hoist=True)
+
+
 # Supports xccl with PyTorch versions >= 2.8.0.dev for XPU platform
 def supports_xccl() -> bool:
     return torch.distributed.is_xccl_available()