[vpr][pack] don't separate chain pattern w/ non-chain

Author: amin1377

vpr/src/pack/prepack.cpp

@@ -1099,47 +1099,33 @@ static AtomBlockId get_sink_block(const AtomBlockId block_id,
     }
 
     const auto& net_sinks = atom_nlist.net_sinks(net_id);
-    if (is_chain_pattern) {
-        // If the pattern is a chain, allow nets with multiple sinks.
-        // This enables forming chains where the COUT is connected both to
-        // the next element in the chain and to the block's output pin.
-        bool connected_to_latch = false;
-        AtomBlockId pattern_sink_block_id = AtomBlockId::INVALID();
-        for (const auto& sink_pin_id : net_sinks) {
-            auto sink_block_id = atom_nlist.pin_block(sink_pin_id);
-            if (atom_nlist.block_model(sink_block_id)->name == std::string(MODEL_LATCH)) {
-                connected_to_latch = true;
-            }
-            if (primitive_type_feasible(sink_block_id, to_pb_type)) {
-                auto to_port_id = atom_nlist.find_atom_port(sink_block_id, to_port_model);
-                auto to_pin_id = atom_nlist.find_pin(to_port_id, BitIndex(to_pin_number));
-                if (to_pin_id == sink_pin_id) {
-                    pattern_sink_block_id = sink_block_id;
-                }
-            }
+    // If the pattern is a chain, allow nets with multiple sinks.
+    // This enables forming chains where the COUT is connected both to
+    // the next element in the chain and to the block's output pin.
+    bool connected_to_latch = false;
+    AtomBlockId pattern_sink_block_id = AtomBlockId::INVALID();
+    for (const auto& sink_pin_id : net_sinks) {
+        auto sink_block_id = atom_nlist.pin_block(sink_pin_id);
+        if (atom_nlist.block_model(sink_block_id)->name == std::string(MODEL_LATCH)) {
+            connected_to_latch = true;
         }
-        // If the number of sinks is greater than 1, and one of the connected blocks is a latch,
-        // then we drop the block to avoid a situation where only registers or unregistered output
-        // of the block can use the output pin.
-        // TODO: This is a conservative assumption, and ideally we need to do analysis of the architecture
-        // before to determine which pattern is supported by the architecture.
-        if (connected_to_latch && net_sinks.size() > 1) {
-            return AtomBlockId::INVALID();
-        }
-        return pattern_sink_block_id;
-    } else {
-        // For non-chain patterns, we conservatively only consider the sink block
-        // if the net fanout is 1. To clarify, consider a case where the output of a LUT
-        // is connected to both a register and an unregistered output that feeds another block.
-        // If the intra-cluster architecture doesn't support having both registered and
-        // unregistered outputs simultaneously, this could lead to a packing failure.
-        if (net_sinks.size() == 1) {
-            auto sink_pin_id = *(net_sinks.begin());
-            return atom_nlist.pin_block(sink_pin_id);
+        if (primitive_type_feasible(sink_block_id, to_pb_type)) {
+            auto to_port_id = atom_nlist.find_atom_port(sink_block_id, to_port_model);
+            auto to_pin_id = atom_nlist.find_pin(to_port_id, BitIndex(to_pin_number));
+            if (to_pin_id == sink_pin_id) {
+                pattern_sink_block_id = sink_block_id;
+            }
         }
     }
-
-    return AtomBlockId::INVALID();
+    // If the number of sinks is greater than 1, and one of the connected blocks is a latch,
+    // then we drop the block to avoid a situation where only registers or unregistered output
+    // of the block can use the output pin.
+    // TODO: This is a conservative assumption, and ideally we need to do analysis of the architecture
+    // before to determine which pattern is supported by the architecture.
+    if (connected_to_latch && net_sinks.size() > 1) {
+        pattern_sink_block_id = AtomBlockId::INVALID();
+    }
+    return pattern_sink_block_id;
 }
 
 /**