drt: Push node index computation up

[kbieganski]

No functional change intended. This speeds up DRT by 3-8%, at least for asap7 (varies depending on the design). Baseline is a recent commit from Oct 6.

asap7/aes - stage 5_2_route - 8 thread(s)

Branch	Min [s]	Median [s]	Relative
Baseline	221.96	222.23	1.03
This PR	215.48	215.91	1.00

asap7/ibex - stage 5_2_route - 8 thread(s)

Branch	Min [s]	Median [s]	Relative
Baseline	337.61	338.30	1.08
This PR	312.99	313.16	1.00

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[kbieganski]

@osamahammad21 Have you had a chance to look at this?

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[kbieganski]

Can this be reviewed?

[maliberty]

@osamahammad21 please review

[kbieganski]

I think each switch is a mix of checked and unchecked accesses (the *Fixed* ones are checked, the *Route* ones aren't). For example, see this part which calls this function. So I was confused by the "safe access" comment, thought it was about something else. Anyway, it seems the checks aren't actually needed?

[kbieganski]

@osamahammad21 In case you missed it

[osamahammad21]

Sorry I didn't notice your comment. It seems that as you said we do not always check the validity of the index which is kind doesn't seem very safe. However, this PR doesn't introduce new problems, So I'll just merge and get back to the index validity later on a separate PR.