[cherry-pick]fix multihead matmul shared params (#27321)

* fix multihead matmul shared params (#27121)

* fix multihead matmul shared params

paddle/fluid/framework/ir/multihead_matmul_fuse_pass.cc

@@ -615,53 +615,62 @@ static int BuildFusionV2(Graph* graph, const std::string& name_scope,
     GET_IR_NODE_FROM_SUBGRAPH(transpose2_qkv_out, transpose2_qkv_out,
                               multihead_pattern);
 
-    fuse_creater(input0, mul0, mul1, mul2, mul0_out, mul1_out, mul2_out, mul0_w,
-                 mul1_w, mul2_w, eltadd0_b, eltadd1_b, eltadd2_b, eltadd_qk_b,
-                 reshape2_0, reshape2_qkv_out, scale, scale_out);
-
-    std::unordered_set<const Node*> marked_nodes({eltadd0,
-                                                  eltadd1,
-                                                  eltadd2,
-                                                  eltadd1_b,
-                                                  eltadd2_b,
-                                                  eltadd0_out,
-                                                  eltadd1_out,
-                                                  eltadd2_out,
-                                                  reshape2_0,
-                                                  reshape2_1,
-                                                  reshape2_2,
-                                                  reshape2_0_out,
-                                                  reshape2_1_out,
-                                                  reshape2_2_out,
-                                                  transpose2_0,
-                                                  transpose2_1,
-                                                  transpose2_2,
-                                                  transpose2_0_out,
-                                                  transpose2_1_out,
-                                                  transpose2_2_out,
-                                                  matmul_qk,
-                                                  matmul_qk_out,
-                                                  eltadd_qk,
-                                                  eltadd_qk_out,
-                                                  softmax_qk,
-                                                  softmax_qk_out,
-                                                  transpose2_qkv,
-                                                  transpose2_qkv_out,
-                                                  matmul_qkv,
-                                                  matmul_qkv_out,
-                                                  mul0,
-                                                  mul1,
-                                                  mul2,
-                                                  mul0_out,
-                                                  mul1_out,
-                                                  mul2_out,
-                                                  mul1_w,
-                                                  mul2_w,
-                                                  reshape2_qkv,
-                                                  scale});
-    // Remove unneeded nodes.
-    GraphSafeRemoveNodes(graph, marked_nodes);
-    ++fusion_count;
+    // If weights or biases in qkv's fc are shared by multiple multihead_matmul
+    // patterns, we do not support this kind of fusion, this pass will not take
+    // effect.
+    bool is_fc_params_shared =
+        mul0_w->outputs.size() > 1 || mul1_w->outputs.size() > 1 ||
+        mul2_w->outputs.size() > 1 || eltadd0_b->outputs.size() > 1 ||
+        eltadd1_b->outputs.size() > 1 || eltadd2_b->outputs.size() > 1;
+    if (!is_fc_params_shared) {
+      fuse_creater(input0, mul0, mul1, mul2, mul0_out, mul1_out, mul2_out,
+                   mul0_w, mul1_w, mul2_w, eltadd0_b, eltadd1_b, eltadd2_b,
+                   eltadd_qk_b, reshape2_0, reshape2_qkv_out, scale, scale_out);
+
+      std::unordered_set<const Node*> marked_nodes({eltadd0,
+                                                    eltadd1,
+                                                    eltadd2,
+                                                    eltadd1_b,
+                                                    eltadd2_b,
+                                                    eltadd0_out,
+                                                    eltadd1_out,
+                                                    eltadd2_out,
+                                                    reshape2_0,
+                                                    reshape2_1,
+                                                    reshape2_2,
+                                                    reshape2_0_out,
+                                                    reshape2_1_out,
+                                                    reshape2_2_out,
+                                                    transpose2_0,
+                                                    transpose2_1,
+                                                    transpose2_2,
+                                                    transpose2_0_out,
+                                                    transpose2_1_out,
+                                                    transpose2_2_out,
+                                                    matmul_qk,
+                                                    matmul_qk_out,
+                                                    eltadd_qk,
+                                                    eltadd_qk_out,
+                                                    softmax_qk,
+                                                    softmax_qk_out,
+                                                    transpose2_qkv,
+                                                    transpose2_qkv_out,
+                                                    matmul_qkv,
+                                                    matmul_qkv_out,
+                                                    mul0,
+                                                    mul1,
+                                                    mul2,
+                                                    mul0_out,
+                                                    mul1_out,
+                                                    mul2_out,
+                                                    mul1_w,
+                                                    mul2_w,
+                                                    reshape2_qkv,
+                                                    scale});
+      // Remove unneeded nodes.
+      GraphSafeRemoveNodes(graph, marked_nodes);
+      ++fusion_count;
+    }
   };
   gpd(graph, handler);