iterating wreduce enters infinite loop about yosys HOT 3 CLOSED

It is not really doing anything here. The "removing top bits" does not actually remove the bits. It changes the wiring around and lets a later "clean" actually get rid of them. When you call "clean" between two calls to "wreduce" then the loop will stop. When you just call "wreduce" in a loop it will prepare this wires in a way that "clean" can get rid of them over and over again.. (It renames the wires, thus it looks like its a different wire in each iteration.)

I have now fixed this in commit 0748ef6. Now wreduce recognizes the already-prepared-for-deletion wires and does not touch them a second time.

from yosys.

Ah, I understand. Perhaps a note about this could be added to the wreduce documentation/output that it needs to be run in conjunction with clean?

while you're at it there is a typo in the title of this page as well (is->if)
http://www.clifford.at/yosys/cmd_wreduce.html

I am under the impression that you are looking for bug reports/typos etc for even minor things, but if you are not, let me know so you can focus on higher priorities.

from yosys.

Perhaps a note about this could be added to the wreduce documentation

This is a general theme in Yosys, not specific to the wreduce command. (The help message to opt_clean has something on it and I've now added some additional explanations to the CodingReadme file.)

while you're at it there is a typo in the title of this page as well

fixed. (webpage will be updated when I release yosys 0.6)

I am under the impression that you are looking for bug reports/typos etc for even minor things, ...

Yes. A steady flow of easy to fix bug reports is very welcome.. ;)

Let me just add a more detailed explanation of what was going on with wreduce (for the record):

Say you have a signal a[5:0] and only the lower 4 bits of it are used, so "wreduce" tries to "remove" the top two bits. I cannot remove a Wire object (or make it shorter, see the explanation in CodingReadme I mentioned above). So I instead create a new wire $temp42[3:0] and essentially add assign $temp42[3:0] = a[3:0] to the design. Finally I rename $temp42 to a and a to $temp42. The next call to "clean" will remove the wire $temp42.

Before my bugfix, if you called "wreduce" a 2nd time it looked at the $temp42[5:0] wire and said "hay - I can remove the two top bits from it", create a $temp43[3:0], assign $temp43[3:0] = $temp42[5:0] and flip the names. Now after the bugfix "wreduce" understands that it is operating on wires that "clean" would throw away anyways and simply skips them.

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