feat: make MIN_PLACE_STEP_COEFF and MAX_PLACE_STEP_COEFF tunable with validation

Signed-off-by: Jack Luar <[email protected]>

Author: luarss

flow/scripts/global_place.tcl

@@ -33,6 +33,25 @@ if { $::env(GPL_TIMING_DRIVEN) } {
   }
 }
 
+# Parameters for phi coefficients in global placement
+# Validate phi coefficient constraints before using them
+if { [info exists ::env(MIN_PLACE_STEP_COEF)] && [info exists ::env(MAX_PLACE_STEP_COEF)] } {
+  set min_phi $::env(MIN_PLACE_STEP_COEF)
+  set max_phi $::env(MAX_PLACE_STEP_COEF)
+
+  if { $min_phi > $max_phi } {
+    utl::error GPL 200 "MIN_PLACE_STEP_COEF ($min_phi) cannot be greater than MAX_PLACE_STEP_COEF ($max_phi)"
+  }
+}
+
+if { [info exists ::env(MIN_PLACE_STEP_COEF)] } {
+  lappend global_placement_args -min_phi_coef $::env(MIN_PLACE_STEP_COEF)
+}
+
+if { [info exists ::env(MAX_PLACE_STEP_COEF)] } {
+  lappend global_placement_args -max_phi_coef $::env(MAX_PLACE_STEP_COEF)
+}
+
 proc do_placement { global_placement_args } {
   set all_args [concat [list -density [place_density_with_lb_addon] \
     -pad_left $::env(CELL_PAD_IN_SITES_GLOBAL_PLACEMENT) \

flow/scripts/variables.yaml

@@ -571,6 +571,30 @@ GPL_ROUTABILITY_DRIVEN:
   stages:
     - place
   default: 1
+MIN_PLACE_STEP_COEF:
+  description: >
+    Sets the minimum phi coefficient (pcof_min / µ_k Lower Bound) for global
+    placement optimization. This parameter controls the step size lower bound
+    in the RePlAce Nesterov optimization algorithm. Lower values may improve
+    convergence but can increase runtime.
+    Valid range: 0.95-1.05
+  default: 0.95
+  stages:
+    - place
+  tunable: 1
+  type: float
+MAX_PLACE_STEP_COEF:
+  description: >
+    Sets the maximum phi coefficient (pcof_max / µ_k Upper Bound) for global
+    placement optimization. This parameter controls the step size upper bound
+    in the RePlAce Nesterov optimization algorithm. Higher values allow more
+    aggressive optimization but may risk divergence.
+    Valid range: 1.00-1.20
+  default: 1.05
+  stages:
+    - place
+  tunable: 1
+  type: float
 CAP_MARGIN:
   description: >
     Specifies a capacitance margin when fixing max capacitance violations. This