further optimization of lstm operator.

src/rewrite_rnn.cpp

@@ -910,19 +910,17 @@ std::vector<instruction_ref> rewrite_rnn::lstm_cell(bool is_forward,
     auto ic_lens = sic->get_shape().lens();
 
     // bias
-    instruction_ref wb{};
-    instruction_ref rb{};
+    instruction_ref wrb{};
     if(bias != prog.end())
     {
 
         auto sbias = prog.insert_instruction(ins, op::squeeze{{0}}, bias);
         auto ub_wb = prog.insert_instruction(ins, op::slice{{0}, {0}, {4 * hs}}, sbias);
         auto ub_rb = prog.insert_instruction(ins, op::slice{{0}, {4 * hs}, {8 * hs}}, sbias);
+        auto ub_wrb = prog.insert_instruction(ins, op::add{}, ub_wb, ub_rb);
 
-        wb = prog.insert_instruction(
-            ins, op::broadcast{1, {bs, 4 * static_cast<size_t>(hs)}}, ub_wb);
-        rb = prog.insert_instruction(
-            ins, op::broadcast{1, {bs, 4 * static_cast<size_t>(hs)}}, ub_rb);
+        wrb = prog.insert_instruction(
+            ins, op::broadcast{1, {bs, 4 * static_cast<size_t>(hs)}}, ub_wrb);
     }
 
     // peep hole
@@ -948,18 +946,12 @@ std::vector<instruction_ref> rewrite_rnn::lstm_cell(bool is_forward,
         auto xt = prog.insert_instruction(ins, op::slice{{0}, {seq_index}, {seq_index + 1}}, seq);
         xt      = prog.insert_instruction(ins, op::squeeze{{0}}, xt);
 
-        instruction_ref xt_sih{};
-        if(bias != prog.end())
-        {
-            auto xt_tsw  = prog.insert_instruction(ins, op::dot{}, xt, tsw, wb);
-            auto sih_tsr = prog.insert_instruction(ins, op::dot{}, sih, tsr, rb);
-            xt_sih       = prog.insert_instruction(ins, op::add{}, xt_tsw, sih_tsr);
-        }
-        else
-        {
         auto xt_tsw  = prog.insert_instruction(ins, op::dot{}, xt, tsw);
         auto sih_tsr = prog.insert_instruction(ins, op::dot{}, sih, tsr);
-            xt_sih       = prog.insert_instruction(ins, op::add{}, xt_tsw, sih_tsr);
+        auto xt_sih       = prog.insert_instruction(ins, op::add{}, xt_tsw, sih_tsr);
+        if(bias != prog.end())
+        {
+            xt_sih       = prog.insert_instruction(ins, op::add{}, xt_sih, wrb);
         }
 
         auto it_before_actv = prog.insert_instruction(ins, op::slice{{1}, {0}, {hs}}, xt_sih);