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Revert "[Bugfix][MoE] Unpad routed output before shared expert add [Fixes #35949]" (#40794) #40853

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Revert "[Bugfix][MoE] Unpad routed output before shared expert add [Fixes #35949]" (#40794) #40853

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6 changes: 0 additions & 6 deletions vllm/model_executor/layers/fused_moe/runner/moe_runner.py
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Original file line number Diff line number Diff line change
Expand Up @@ -550,14 +550,10 @@ def forward(
hidden_states
)

# Record before `_maybe_pad_hidden_states` pads activations to match
# `moe_config.hidden_dim`, e.g. after `align_trtllm_fp4_moe_hidden_dim_for_fi`
routed_hidden_dim = hidden_states.shape[-1]
hidden_states, og_hidden_dim = self._maybe_pad_hidden_states(
shared_experts_input,
hidden_states,
)
Comment on lines 553 to 556
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@gemini-code-assist gemini-code-assist Bot Apr 25, 2026

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high

Reverting the padding detection logic re-introduces a bug where fused_output and shared_output have mismatched dimensions when padding is applied (Fixes #35949). Instead of a full revert, these variables should be retained to allow for proper unpadding before the outputs are combined.

        # Record before `_maybe_pad_hidden_states` pads activations to match
        # `moe_config.hidden_dim`, e.g. after `align_trtllm_fp4_moe_hidden_dim_for_fi`
        routed_hidden_dim = hidden_states.shape[-1]
        hidden_states, og_hidden_dim = self._maybe_pad_hidden_states(
            shared_experts_input,
            hidden_states,
        )
        hidden_dim_was_padded = hidden_states.shape[-1] > routed_hidden_dim

hidden_dim_was_padded = hidden_states.shape[-1] > routed_hidden_dim

result = self._forward_entry(
hidden_states,
Expand All @@ -577,8 +573,6 @@ def forward(

# Extract outputs from result
shared_output, fused_output = _unpack(result)
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@gemini-code-assist gemini-code-assist Bot Apr 25, 2026

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high

The RuntimeError and garbled output reported in CI are caused by the non-contiguous tensor produced by slicing fused_output. Adding .contiguous() after the slice resolves these issues while maintaining the fix for shape mismatch during the addition of shared and routed expert outputs.

Suggested change
shared_output, fused_output = _unpack(result)
shared_output, fused_output = _unpack(result)
if hidden_dim_was_padded:
fused_output = fused_output[..., :routed_hidden_dim].contiguous()

if hidden_dim_was_padded:
fused_output = fused_output[..., :routed_hidden_dim]

# If combine kernel already reduced fused, reduce shared to match.
# See note above re: the two all-reduce points.
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