Re: [Iverilog-devel] Always blocks with out delays (pr1862744)

[Stephen W. <st...@ic...>]

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This sounds intriguing. I think this attribute would better be
attached to the NetProc base class because a thorough check for
the warning will get better information from elaborated results.
For example, elaboration of a process will include precomputing
constant expressions and that may allow catching infinite for-
and while-loops. Also, task definitions will be available as
elaborated NetProc objects.

I would sat that non-blocking assignments have zero delay, by
the way, because they do not block execution. I think you mean
that blocking assignments with internal delays should return
has_delay of true, because they do have delay, and they pause
the thread.

By the way, this handling can also be used to detect the
erroneous case of a user defined function that *has* a delay.
This is illegal but currently it is not detected and reported.

Cary R. wrote:
| I have been thinking about this for a while and here is what I have
come up with so far. We need to add a new attribute to the P* objects
'has_delay' that the always command can use to print a warning if the
block appears to not have some kind of delay.
|
| The default object type will be no delay. Delay, non-blocking
assignment and wait statements will return true. An if or switch
statement will only return true if there is a delay in all paths. We
don't know the logic so this is the safest choice. Except for a repeat
with a constant positive value, loops always return false for the same
reason (they may not run). The repeat mentioned above will only return
true if it contains a statement that has a delay. Task calls (tasks) and
blocks return true if one of their items returns has a delay.
|
| It could be argued that a forever or a while with a constant true
value should also return true, but using them inside an always seems
dubious at best.
|
| For the delay elements we should probably check that the delay is not
zero. This should be easy for a constant value. For variable delays I
think we just have to trust that the user is doing the right thing and
assume the delay is greater than zero.
|
| Does this make sense? Am I missing anything. The message will be a
warning that the always block could create an infinite loop.



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