open: skip CRPR pre-CTS to avoid OOM on high-reconvergence clocks

Pre-CTS there is no clock tree, so CRPR (clock reconvergence pessimism
removal) has no real launch/capture common-path delay to remove and its
correction is ~0. On designs with high clock reconvergence the CRPR tag
set can still grow to tens of GB and OOM the process while contributing
nothing to the reported slacks.

Disable CRPR for design_stage < 4, mirroring the existing
set_propagated_clock gate. At stage >= 4 (CTS onward) CRPR is unchanged.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

flow/scripts/open.tcl

@@ -53,6 +53,12 @@ proc read_timing { input_file } {
   if { $design_stage >= 4 } {
     # CTS has run, so propagate clocks
     set_propagated_clock [all_clocks]
+  } else {
+    # Pre-CTS there is no clock tree, so CRPR has no real launch/capture
+    # common-path delay to remove and its correction is ~0. On designs with
+    # high clock reconvergence the CRPR tag set can still grow to tens of GB
+    # and OOM the process. Skip it pre-CTS.
+    sta::set_crpr_enabled 0
   }
 
   if { $design_stage >= 6 && [file exist $::env(RESULTS_DIR)/6_final.spef] } {