asap7/riscv32i adder map logic and optimization with resizer

[vijayank88]

I am working on asap7/riscv32i design with different manual macro placement for lab exercise tutorial. Trying to fix timing violations with multiple variables.

The following max path not optimized during placement stage,

Startpoint: instr[4] (input port clocked by clk)
Endpoint: riscv/dp/_18865_ (falling edge-triggered flip-flop clocked by clk')
Path Group: clk
Path Type: max

With default setup timing reports as follows,

Placement: 3_4_place_resized.log

resizer pre report_tns
--------------------------------------------------------------------------
tns -2397732.00

===========================================
resizer pre report_wns
--------------------------------------------------------------------------
wns -2213.90

resizer report_tns
--------------------------------------------------------------------------
tns -53198.47

==========================================
resizer report_wns
--------------------------------------------------------------------------
wns -122.88

CTS report: 4_1_cts.log

cts post-repair check_setup
--------------------------------------------------------------------------

===========================================
cts post-repair report_tns
--------------------------------------------------------------------------
tns -53319.00

===========================================
cts post-repair report_wns
--------------------------------------------------------------------------
wns -123.62

Post Route Report: 6_report.log

finish report_tns
--------------------------------------------------------------------------
tns -40196.54

===========================================
finish report_wns
--------------------------------------------------------------------------
wns -96.24

If I remove adder map logic, there is no negative slack.

Placement: 3_4_place_resized.log

resizer pre report_tns
--------------------------------------------------------------------------
tns -4643115.50

============================================
resizer pre report_wns
--------------------------------------------------------------------------
wns -4067.38

resizer report_tns
--------------------------------------------------------------------------
tns 0.00

==========================================
resizer report_wns
--------------------------------------------------------------------------
wns 0.00

===========================================
resizer report_worst_slack
--------------------------------------------------------------------------
worst slack 87.63

CTS report: 4_1_cts.log

cts post-repair report_tns
--------------------------------------------------------------------------
tns 0.00

============================================
cts post-repair report_wns
--------------------------------------------------------------------------
wns 0.00

===========================================
cts post-repair report_worst_slack
--------------------------------------------------------------------------
worst slack 113.32

Post Route Report: 6_report.log

finish report_tns
--------------------------------------------------------------------------
tns 0.00

============================================
finish report_wns
--------------------------------------------------------------------------
wns 0.00

============================================
finish report_worst_slack
--------------------------------------------------------------------------
worst slack 52.40

So where the issue coming from?

1. Yosys ADDER_MAP_FILE?
2. Resizer has issue with optimization of FA/HA logic?

cc\ @maliberty @gadfort

[maliberty]

This would be better filed as an issue.

[vijayank88]

#1434 created an issue.