moved setundef -zero before ABC optimization to resolve undefined values before ABC

This fixes the Yosys issue 5220.

Signed-off-by: Cho Moon <[email protected]>

Author: precisionmoon

flow/scripts/synth.tcl

@@ -107,6 +107,9 @@ if { [env_var_exists_and_non_empty DFF_LIB_FILE] } {
 }
 opt
 
+# Replace undef values with defined constants
+setundef -zero
+
 if { ![env_var_exists_and_non_empty SYNTH_WRAPPED_OPERATORS] } {
   log_cmd abc {*}$abc_args
 } else {
@@ -117,9 +120,6 @@ if { ![env_var_exists_and_non_empty SYNTH_WRAPPED_OPERATORS] } {
   delete {t:$specify*}
 }
 
-# Replace undef values with defined constants
-setundef -zero
-
 # Splitting nets resolves unwanted compound assign statements in netlist (assign {..} = {..})
 splitnets