Sdc pick algorithm

[oharboe]

Manually tested with the instrumentation below.

$ git diff
diff --git a/flow/scripts/util.tcl b/flow/scripts/util.tcl
index ec972778..a6c3a22c 100644
--- a/flow/scripts/util.tcl
+++ b/flow/scripts/util.tcl
@@ -82,6 +82,7 @@ proc find_sdc_file {input_file} {
       break
     }
   }
+  # puts "Using $sdc_file"
   return [list $design_stage $sdc_file]
 }
$ make  ABSTRACT_SOURCE=3_place do-generate_abstract
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/3_place.sdc
$ make  ABSTRACT_SOURCE=2_floorplan do-generate_abstract
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/2_floorplan.sdc
$ make  ABSTRACT_SOURCE=2_1_floorplan do-generate_abstract
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/2_1_floorplan.sdc
$ make  ABSTRACT_SOURCE=5_1_grt do-generate_abstract
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/5_1_grt.sdc
$ make  ABSTRACT_SOURCE=4_cts do-generate_abstract
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/4_cts.sdc
$ make gui_5_1_grt
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/5_1_grt.sdc
$ make gui_route
Using /home/oyvind/OpenROAD-flow-scripts/flow/results/nangate45/gcd/base/5_route.sdc

[oharboe]

@jeffng-or FYI, fixes this error in MegaBoom:

$ tmp/make gui_grt
ODB_FILE=.//results/asap7/lb_32x128/base/5_1_grt.odb /home/oyvind/OpenROAD-flow-scripts/tools/install/OpenROAD/bin/openroad -no_init -threads 48  /home/oyvind/OpenROAD-flow-scripts/flow/scripts/open.tcl
OpenROAD v2.0-16787-gcd519bb5e 
Features included (+) or not (-): +Charts +GPU +GUI +Python
This program is licensed under the BSD-3 license. See the LICENSE file for details.
Components of this program may be licensed under more restrictive licenses which must be honored.
[INFO ORD-0030] Using 48 thread(s).
GUI_TIMING=1 reading timing, takes a little while for large designs...
Error: open.tcl, 64 can't read "::env(SDC_FILE)": no such variable
openroad> 

[maliberty]

Conflicts to resolve