(replacing assertions)
The IEEE standard either requires out-of-bounds bits to be ignored on
write, returned as 1'bx on read, or requires a compile-time error message.
The latter is easier to implement.
(cherry picked from commit 7d7aa0604c)
An out-of-range constant bit select on the LHS of an assignment was being
treated as an error, whereas an out-of range constant part select would
only result in a warning. In any other context, either case would result
in a warning, so convert the error to a warning.
In addition, all warnings for out-of-range or undefined constant bit/part
selects should be controlled by -Wselect-range.
A compressed assignment statement should give exactly the same
result as the equivalent uncompressed statement. This means
that the type (signed/unsigned) of the LHS affects the type of
the RHS expression (unlike in normal assignments). We need to
take care that bit/part selects and concatenations are correctly
identified as unsigned values, even in the cases where they
reduce to a single whole signal.
If the l-value is an unresolved wire, then elaboration can allow
the assignment as long as it is to bits that are not otherwise
driven. Handle this in some simple cases.
This gets nested l-values to (but just short of) the ivl_target API.
Now the elaborator can process nested l-values, but I haven't figured
out how to present that at the ivl_target.h API.
Static properties are like variables in a named scope.
Detect these variables during elaboration so that the
code generator just sees them as variables.
This implementation works by detecting assignments
to constant properties in elaboration. Allow initializer
assignments to assign to the constant, error all other
assignments, and otherwise treat the constant like any
other property.
For constant bit/part selects, issue a warning if the select is out
of range or an undefined value. In any case, the RHS value should be
discarded, and the actual assignment should be skipped.
For constant word indices, issue a warning if the index is out of
range or an undefined value. In any case, the RHS value should be
discarded, and the actual assignment should be skipped.
Martin Whitaker
Stephen Williams
Cary R
Larry Doolittle