make repair_timing fail early on futile setup repair

[oharboe]

Description

When putting a design under CI early, it is useful to run through CTS quickly to get a macro abstract so that floorplanning can proceed indepenently of solving timing issues down at the macro level.

In the case below, looking at the WNS for a clock period of 1000, the setup repair is obviously futile. repair_timing could give up more quickly.

repair_timing does give up on hold as the 20% buffer threshold is met, but the hold repair happens after a lengthy futile setup repair attempt.

repair_timing -verbose -repair_tns 0
[INFO RSZ-0094] Found 2261 endpoints with setup violations.
Iteration | Resized | Buffers | Cloned Gates | Pin Swaps |   WNS   |   TNS   | Endpoint
---------------------------------------------------------------------------------------
        0 |       0 |       0 |            0 |         0 | -9331.476 | -6446508.000 | io_...
       10 |       3 |       0 |            2 |         4 | -9292.986 | -6428689.000 | io_...
       20 |      11 |       0 |            4 |         4 | -9263.688 | -6393942.000 | io_...
       30 |      15 |       0 |            9 |         5 | -9208.877 | -6361912.500 | io_...
       40 |      21 |       0 |           13 |         5 | -9176.483 | -6351535.000 | io_...
       50 |      26 |       0 |           16 |         7 | -9170.731 | -6349262.000 | io_...
       60 |      34 |       0 |           18 |         7 | -9158.175 | -6341483.000 | io_...
       70 |      44 |       0 |           18 |         7 | -9150.161 | -6335393.000 | io_...
       80 |      51 |       2 |           20 |         7 | -9142.903 | -6327522.500 | io_...
       90 |      55 |       2 |           24 |         9 | -9108.962 | -6310355.000 | io_...
      100 |      59 |       6 |           27 |        10 | -9091.226 | -6298352.000 | io_...
      110 |      62 |       8 |           31 |        12 | -9073.103 | -6288537.500 | io_...
      120 |      65 |      19 |           35 |        12 | -9014.830 | -6239610.000 | io_...
      130 |      66 |      19 |           41 |        15 | -8979.107 | -6225933.500 | io_...
      140 |      67 |      23 |           47 |        16 | -8967.909 | -6217542.500 | io_...
      150 |      67 |      23 |           53 |        20 | -8956.291 | -6208358.000 | io_...
      160 |      68 |      25 |           56 |        24 | -8937.215 | -6198154.500 | io_...
      170 |      68 |      29 |           62 |        25 | -8909.112 | -6181045.000 | io_...
      180 |      68 |      38 |           62 |        27 | -8930.631 | -6185781.500 | io_...
      190 |      70 |      41 |           66 |        28 | -8935.765 | -6188781.000 | io_...
      200 |      75 |      46 |           68 |        28 | -8929.567 | -6187565.000 | io_...
      210 |      77 |      53 |           71 |        29 | -8925.813 | -6187079.500 | io_...
      220 |      80 |      58 |           74 |        29 | -8933.716 | -6184588.000 | io_...
      230 |      80 |      63 |           76 |        32 | -8974.421 | -6191987.000 | io_...
      240 |      80 |      73 |           76 |        32 | -9060.264 | -6219459.000 | io_...
      250 |      80 |      83 |           76 |        32 | -9146.106 | -6246929.500 | io_...
      260 |      80 |      93 |           76 |        32 | -9231.948 | -6274394.000 | io_...
      265 |      79 |      55 |           73 |        32 | -8899.399 | -6170303.000 | io_...
    final |      79 |      55 |           73 |        32 | -8899.670 | -6171126.000 | io_...
---------------------------------------------------------------------------------------
[INFO RSZ-0045] Inserted 41 buffers, 1 to split loads.
[INFO RSZ-0041] Resized 79 instances.
[INFO RSZ-0043] Swapped pins on 32 instances.
[INFO RSZ-0049] Cloned 73 instances.
[WARNING RSZ-0062] Unable to repair all setup violations.
[INFO RSZ-0046] Found 5011 endpoints with hold violations.
Iteration | Resized | Buffers | Cloned Gates |   WNS   |   TNS   | Endpoint
---------------------------------------------------------------------------
        0 |       0 |       0 |            0 | -281.233 | -858598.125 | doohickey...$_DFF_P_/D
    final |      18 |   26464 |            0 | -143.998 | -388767.750 | doohickey...$_DFFE_PN_/D
---------------------------------------------------------------------------
[WARNING RSZ-0066] Unable to repair all hold violations.
[INFO RSZ-0032] Inserted 26464 hold buffers.
[ERROR RSZ-0060] Max buffer count reached.
Error: cts.tcl, 86 RSZ-0060

Suggested Solution

Make repair_timing fail quickly with clear and actionable error message when there is no hope.

A fast failing timing repair in CTS indicates to the user that for now the abstract has to be made immediately after make place.

Additional Context

No response