diff --git a/gowin/arch.cc b/gowin/arch.cc
index 727ed0af..991390ce 100644
--- a/gowin/arch.cc
+++ b/gowin/arch.cc
@@ -1205,7 +1205,6 @@ void Arch::assignArchInfo()
         } else {
             ci->is_slice = false;
         }
-        ci->user_group = int_or_default(ci->attrs, id("PACK_GROUP"), -1);
     }
 }
 
@@ -1220,8 +1219,7 @@ bool Arch::cellsCompatible(const CellInfo **cells, int count) const
         if (ci->is_slice && ci->slice_clk != nullptr) {
             Loc loc = getBelLocation(ci->bel);
             int cls = loc.z / 2;
-            bool ff_used = ci->params.at(id_FF_USED).as_bool();
-            if (loc.z >= 6 && ff_used) // top slice have no ff
+            if (loc.z >= 6 && ci->ff_used) // top slice have no ff
                 return false;
             if (clk[cls] == nullptr)
                 clk[cls] = ci->slice_clk;
@@ -1236,12 +1234,6 @@ bool Arch::cellsCompatible(const CellInfo **cells, int count) const
             else if (lsr[cls] != ci->slice_lsr)
                 return false;
         }
-        if (ci->user_group != -1) {
-            if (group == -1)
-                group = ci->user_group;
-            else if (group != ci->user_group)
-                return false;
-        }
     }
     return true;
 }
diff --git a/gowin/archdefs.h b/gowin/archdefs.h
index 458be682..5582d5cf 100644
--- a/gowin/archdefs.h
+++ b/gowin/archdefs.h
@@ -81,9 +81,8 @@ struct NetInfo;
 
 struct ArchCellInfo
 {
-    // Custom grouping set via "PACK_GROUP" attribute. All cells with the same group
-    // value may share a tile (-1 = don't care, default if not set)
-    int user_group;
+    // Is the flip-flop of this slice used
+    bool ff_used;
     // Is a slice type primitive
     bool is_slice;
     // Only packing rule for slice type primitives is a single clock per tile
diff --git a/gowin/cells.cc b/gowin/cells.cc
index db7154a0..2fd103bf 100644
--- a/gowin/cells.cc
+++ b/gowin/cells.cc
@@ -44,8 +44,8 @@ std::unique_ptr<CellInfo> create_generic_cell(Context *ctx, IdString type, std::
     new_cell->type = type;
     if (type == id_SLICE) {
         new_cell->params[id_INIT] = 0;
-        new_cell->params[id_FF_USED] = 0;
         new_cell->params[id_FF_TYPE] = id_DFF.str(ctx);
+        new_cell->ff_used = false;
 
         IdString names[4] = {id_A, id_B, id_C, id_D};
         for (int i = 0; i < 4; i++) {
@@ -84,14 +84,14 @@ void lut_to_lc(const Context *ctx, CellInfo *lut, CellInfo *lc, bool no_dff)
     }
 
     if (no_dff) {
-        lc->params[id_FF_USED] = 0;
+        lc->ff_used = false;
         replace_port(lut, id_F, lc, id_F);
     }
 }
 
 void dff_to_lc(const Context *ctx, CellInfo *dff, CellInfo *lc, bool pass_thru_lut)
 {
-    lc->params[id_FF_USED] = 1;
+    lc->ff_used = true;
     lc->params[id_FF_TYPE] = dff->type.str(ctx);
     replace_port(dff, id_CLK, lc, id_CLK);
     replace_port(dff, id_CE, lc, id_CE);
diff --git a/gowin/constids.inc b/gowin/constids.inc
index 8bc5efdd..765b8f06 100644
--- a/gowin/constids.inc
+++ b/gowin/constids.inc
@@ -388,7 +388,6 @@ X(TBUF)
 
 // primitive attributes
 X(INIT)
-X(FF_USED)
 X(FF_TYPE)
 X(INPUT_USED)
 X(OUTPUT_USED)