add env var to prevent erasing non-stage variables

Signed-off-by: Eder Monteiro <[email protected]>

Author: eder-matheus

flow/scripts/util.tcl

@@ -145,6 +145,9 @@ proc find_macros { } {
 }
 
 proc erase_non_stage_variables { stage_name } {
+  if { [info exists ::env(KEEP_VARS)] && $::env(KEEP_VARS) == 1 } {
+    return
+  }
   # "$::env(SCRIPTS_DIR)/stage_variables.py stage_name" returns list of
   # variables to erase.
   #

flow/scripts/variables.yaml

@@ -1231,3 +1231,10 @@ NUM_CORES:
     routing, or place jobs running at the same time.
   stages:
     - All stages
+KEEP_VARS:
+  description: >
+    Feature toggle to keep intermediate variables during the flow.
+    This is useful for the single-run flow, where all stages of the flow
+    are run in a single OpenROAD instance.
+  stages:
+    - All stages