[https://nvbugs/6633931][fix] Size the SM90 fp8 block-scale MoE workspace for the buffers it actually uses

cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu

@@ -3332,33 +3332,35 @@ CutlassMoeFCRunner<T, WeightType, OutputType, InputType, BackBoneType, Enable>::
         size_t factor = is_gated_activation ? 2 : 1;
         size_t blockscale_fc1_output_size = factor * interbuf_elems * gemm_output_dtype;
         size_t blockscale_fc2_output_size = permuted_elems * gemm_output_dtype;
-        overlapped_gemm1_gemm2_inputs_size
-            = std::max(std::max(permuted_data_size, fc1_result_size), blockscale_fc2_output_size);
-        // The fused pre-FC2 path writes the FC2 GEMM output into the outputs buffer (glu_inter_result_)
-        // instead of the aliased fc2_result_, so size it for the larger of the FC1 raw output and the
-        // FC2 output.
-        overlapped_gemm1_gemm2_outputs_size = std::max(blockscale_fc1_output_size, blockscale_fc2_output_size);
+        overlapped_gemm1_gemm2_inputs_size = std::max(permuted_data_size, fc1_result_size);
+        overlapped_gemm1_gemm2_outputs_size = blockscale_fc1_output_size;
 
         auto* blockscale_gemm_runner = getDeepSeekBlockScaleGemmRunner();
         TLLM_CHECK(blockscale_gemm_runner != nullptr);
         // getWorkspaceSize also sets the runner's 1x128 scale leading dim (getActScaleLeadingDim()); the dim
         // depends only on (num_rows, top_k, num_experts) so it is shape_k-independent and shared by FC1/FC2.
         if (blockscale_gemm_runner->isActivationPrequantized())
         {
+            // FC2's input (fc1_result_) is aliased onto fc2_result_ in the inputs buffer, so FC2 writes
+            // its output into the outputs buffer (glu_inter_result_).
+            overlapped_gemm1_gemm2_outputs_size = std::max(blockscale_fc1_output_size, blockscale_fc2_output_size);
             // Fused: the runner needs no internal workspace (both operands pre-quantized). The fused quant
             // instead packs fp8 activations + the padded 1x128 scales into the overlapped inputs buffer
             // (fc1_result_ for FC2, permuted_data_ for FC1); size it for both (hidden_size > inter_size makes
-            // FC1 dominant). The scale leading dim (~num_experts*32) can dwarf the token count, so it is not
-            // covered by the bf16-activation size.
+            // FC1 dominant). The scale leading dim (~num_experts*32) can dwarf the token count. The buffer
+            // holds these fp8 regions only, never the bf16 activations.
             blockscale_gemm_runner->getWorkspaceSize(
                 num_rows, hidden_size, inter_size, experts_per_token, num_experts_per_node);
             int64_t const scale_leading_dim = blockscale_gemm_runner->getActScaleLeadingDim();
-            overlapped_gemm1_gemm2_inputs_size = std::max({overlapped_gemm1_gemm2_inputs_size,
-                fp8BlockScaleRegionBytes(num_moe_inputs, inter_size, scale_leading_dim),
-                fp8BlockScaleRegionBytes(num_moe_inputs, hidden_size, scale_leading_dim)});
+            overlapped_gemm1_gemm2_inputs_size
+                = std::max(fp8BlockScaleRegionBytes(num_moe_inputs, inter_size, scale_leading_dim),
+                    fp8BlockScaleRegionBytes(num_moe_inputs, hidden_size, scale_leading_dim));
         }
         else
         {
+            // FC2 writes fc2_result_, which is aliased into the inputs buffer.
+            overlapped_gemm1_gemm2_inputs_size
+                = std::max(overlapped_gemm1_gemm2_inputs_size, blockscale_fc2_output_size);
             // Unfused: the <bf16,fp8,bf16> runner quantizes A internally into deepseek_fc_workspace.
             auto deepseek_fc1_workspace_size = blockscale_gemm_runner->getWorkspaceSize(
                 num_rows, factor * inter_size, hidden_size, experts_per_token, num_experts_per_node);