abc: add -retime with speed script

Signed-off-by: Øyvind Harboe <[email protected]>

flow/scripts/synth_preamble.tcl

@@ -63,19 +63,21 @@ if {[env_var_exists_and_non_empty PRESERVE_CELLS]} {
   }
 }
 
+set abc_args {}
+
 if {$::env(ABC_AREA)} {
   puts "Using ABC area script."
-  set abc_script $::env(SCRIPTS_DIR)/abc_area.script
+  lappend abc_args -script $::env(SCRIPTS_DIR)/abc_area.script
 } else {
   puts "Using ABC speed script."
-  set abc_script $::env(SCRIPTS_DIR)/abc_speed.script
+  lappend abc_args -script $::env(SCRIPTS_DIR)/abc_speed.script
+  lappend abc_args -retime
 }
 
 # Technology mapping for cells
 # ABC supports multiple liberty files, but the hook from Yosys to ABC doesn't
-set abc_args [list -script $abc_script \
-      -liberty $::env(DONT_USE_SC_LIB) \
-      -constr $::env(OBJECTS_DIR)/abc.constr]
+lappend abc_args -liberty $::env(DONT_USE_SC_LIB)
+lappend abc_args -constr $::env(OBJECTS_DIR)/abc.constr
 
 # Exclude dont_use cells. This includes macros that are specified via
 # LIB_FILES and ADDITIONAL_LIBS that are included in LIB_FILES.