grt: add option to skip large fanout nets

src/grt/README.md

@@ -24,6 +24,7 @@ global_route
     [-congestion_report_iter_step steps]
     [-grid_origin {x y}]
     [-critical_nets_percentage percent]
+    [-skip_large_fanout_nets fanout]
     [-allow_congestion]
     [-verbose]
     [-start_incremental]
@@ -42,6 +43,7 @@ global_route
 | `-congestion_report_iter_step` | Set the number of iterations to report. The default value is `0`, and the allowed values are integers `[0, MAX_INT]`. |
 | `-grid_origin` | Set the (x, y) origin of the routing grid in DBU. For example, `-grid_origin {1 1}` corresponds to the die (0, 0) + 1 DBU in each x--, y- direction. |
 | `-critical_nets_percentage` | Set the percentage of nets with the worst slack value that are considered timing critical, having preference over other nets during congestion iterations (e.g. `-critical_nets_percentage 30`). The default value is `0`, and the allowed values are integers `[0, MAX_INT]`. |
+| `-skip_large_fanout_nets` | Skips routing for nets with a fanout higher than the specified limit. Nets exceeding this pin count threshold will be ignored by the global router. The default value is `-1`, and the allowed values are integers `[0, MAX_INT]`. |
 | `-allow_congestion` | Allow global routing results to be generated with remaining congestion. The default is false. |
 | `-verbose` | This flag enables the full reporting of the global routing. |
 | `-start_incremental` | This flag initializes the GRT listener to get the net modified. The default is false. |

src/grt/include/grt/GlobalRouter.h

@@ -154,6 +154,10 @@ class GlobalRouter
   void setResistanceAware(bool resistance_aware);
   void setMacroExtension(int macro_extension);
   void setUseCUGR(bool use_cugr) { use_cugr_ = use_cugr; };
+  void setSkipLargeFanoutNets(int skip_large_fanout)
+  {
+    skip_large_fanout_ = skip_large_fanout;
+  };
 
   // flow functions
   void readGuides(const char* file_name);
@@ -495,6 +499,7 @@ class GlobalRouter
   int total_diodes_count_;
   bool is_congested_{false};
   bool use_cugr_{false};
+  int skip_large_fanout_{-1};
 
   // Region adjustment variables
   std::vector<RegionAdjustment> region_adjustments_;

src/grt/src/GlobalRouter.cpp

@@ -3744,6 +3744,9 @@ std::vector<Net*> GlobalRouter::findNets(bool init_clock_nets)
   }
   std::vector<Net*> clk_nets;
   for (odb::dbNet* db_net : db_nets) {
+    if (skip_large_fanout_ > 0 && db_net->getTermCount() > skip_large_fanout_) {
+      continue;
+    }
     Net* net = addNet(db_net);
     // add clock nets not connected to a leaf first
     if (net) {

src/grt/src/GlobalRouter.i

@@ -146,6 +146,12 @@ set_use_cugr(bool use_cugr)
   getGlobalRouter()->setUseCUGR(use_cugr);
 }
 
+void
+set_skip_large_fanout(int skip_large_fanout)
+{
+  getGlobalRouter()->setSkipLargeFanoutNets(skip_large_fanout);
+}
+
 void
 global_route(bool start_incremental, bool end_incremental)
 {

src/grt/src/GlobalRouter.tcl

@@ -146,6 +146,7 @@ sta::define_cmd_args "global_route" {[-guide_file out_file] \
                                   [-congestion_report_iter_step steps] \
                                   [-grid_origin origin] \
                                   [-critical_nets_percentage percent] \
+                                  [-skip_large_fanout_nets fanout] \
                                   [-allow_congestion] \
                                   [-verbose] \
                                   [-start_incremental] \
@@ -157,7 +158,8 @@ sta::define_cmd_args "global_route" {[-guide_file out_file] \
 proc global_route { args } {
   sta::parse_key_args "global_route" args \
     keys {-guide_file -congestion_iterations -congestion_report_file \
-          -grid_origin -critical_nets_percentage -congestion_report_iter_step
+          -grid_origin -critical_nets_percentage -congestion_report_iter_step\
+          -skip_large_fanout_nets
          } \
     flags {-allow_congestion -resistance_aware -verbose -start_incremental -end_incremental \
           -use_cugr}
@@ -214,6 +216,12 @@ proc global_route { args } {
 
   grt::set_use_cugr [info exists flags(-use_cugr)]
 
+  if { [info exists keys(-skip_large_fanout_nets)] } {
+    set fanout $keys(-skip_large_fanout_nets)
+    sta::check_positive_integer "-skip_large_fanout_nets" $fanout
+    grt::set_skip_large_fanout $fanout
+  }
+
   set allow_congestion [info exists flags(-allow_congestion)]
   grt::set_allow_congestion $allow_congestion
 

src/grt/test/BUILD

@@ -78,6 +78,7 @@ TESTS = [
     "set_nets_to_route1",
     "silence",
     "single_row",
+    "skip_large_fanout1",
     "soft_ndr_4w_6s",
     "top_level_term1",
     "top_level_term2",

src/grt/test/CMakeLists.txt

@@ -76,6 +76,7 @@ or_integration_tests(
     set_nets_to_route1
     silence
     single_row
+    skip_large_fanout1
     soft_ndr_4w_6s
     top_level_term1
     top_level_term2