fix double sb from fifo rotations during intra coissue

1 files changed, 18 insertions, 0 deletions

diff --git a/src/abstract_hardware_model.cc b/src/abstract_hardware_model.cc
index b164c73..970cc62 100644
--- a/src/abstract_hardware_model.cc
+++ b/src/abstract_hardware_model.cc
@@ -2792,6 +2792,12 @@ void simt_tables::update(simt_mask_t &thread_done, addr_vector_t &next_pc,
 
   std::map<address_type, simt_mask_t> divergent_paths;
   bool do_invalidate = false;
+  // Mode 2 (slot-pinned scoreboard) drain gate: set true if this update
+  // actually mutates FIFO membership (divergence, reconvergence, CALL,
+  // RET). Plain linear advance / branch-taken with no divergence does NOT
+  // set this. Co-issue's move_split_to_front does not go through update()
+  // at all, so it cannot set this.
+  bool fifo_membership_changed = false;
 
   while (top_active_mask.any()) {
     address_type tmp_next_pc = null_pc;
@@ -2860,12 +2866,14 @@ void simt_tables::update(simt_mask_t &thread_done, addr_vector_t &next_pc,
         new_st_entry.m_branch_div_cycle = gpgpusim_total_cycles;
         new_st_entry.m_type = SPLITS_TABLE_TYPE_CALL;
         m_simt_splits_table->insert_new_entry(new_st_entry);
+        m_div_recv_drain_pending = true;  // CALL changes FIFO membership
         return;
       } else if (next_inst_op == RET_OPS &&
                  top_type == SPLITS_TABLE_TYPE_CALL) {
         assert(num_divergent_paths == 1);
         top_recvg_entry = m_simt_splits_table->get_rpc_entry();
         m_simt_splits_table->invalidate();
+        fifo_membership_changed = true;  // RET changes FIFO membership
 
         simt_mask_t active_mask =
             m_simt_recvg_table->get_active_mask(new_recvg_entry);
@@ -2901,6 +2909,7 @@ void simt_tables::update(simt_mask_t &thread_done, addr_vector_t &next_pc,
             m_simt_recvg_table->get_type(top_recvg_entry);
         m_simt_splits_table->insert_new_entry(pc, rpc, rpc_entry, active_mask,
                                               type, true);
+        fifo_membership_changed = true;  // reconvergence inserts merged split
       }
       if (num_divergent_paths == 1) {
         if (!do_invalidate) {
@@ -2936,6 +2945,7 @@ void simt_tables::update(simt_mask_t &thread_done, addr_vector_t &next_pc,
             m_simt_recvg_table->get_type(new_recvg_entry);
         m_simt_splits_table->insert_new_entry(pc, rpc, rpc_entry, active_mask,
                                               type);
+        fifo_membership_changed = true;  // reconvergence inserts merged split
       }
       continue;
     }
@@ -2957,6 +2967,14 @@ void simt_tables::update(simt_mask_t &thread_done, addr_vector_t &next_pc,
 
   if (do_invalidate) m_simt_splits_table->update_active_entry();
 
+  // Mode 2 drain gate: divergence (>1 paths) or any reconvergence/CALL/RET
+  // path observed above sets the flag so the next fetch into either ibuffer
+  // half for this warp waits for both slot scoreboards to drain. CALL_OPS
+  // already returned with the flag set; reach here only for normal paths.
+  if (warp_diverged || fifo_membership_changed) {
+    m_div_recv_drain_pending = true;
+  }
+
   check_simt_tables();
 
   m_shader->update_st_size(m_simt_splits_table->num_entries());