The ID(OVERFLOW) IdString isn't used widely enough that we require a
statically allocated IdString, but I think it's good to have an example
workaround in place in case more collisions come up.
I've used this shell command to obtain the list:
rg -I -t cpp -t yacc -o \
'ID\((\$?[a-zA-Z0-9_]+)\)|ID::($?[a-zA-Z0-9_]+)' -r 'X($1$2)' \
| LC_ALL=C sort -u
This removed the entries X(_TECHMAP_FAIL_) and X(nomem2init).
The vast majority of ID(...) uses are in a context that is overloaded
for StaticIdString or will cause implicit conversion to an IdString
constant reference. For some sufficently overloaded contexts, implicit
conversion may fail, so it's useful to have a method to force obtaining
a `IdString const &` from an ID(...) use.
When turning all literal IdStrings of the codebase into StaticIdStrings
this was needed in exactly one place, for which this commit adds an
`id_string()` call.
The simple XOR `commutative_eat()` implementation produces a lot of collisions.
https://www.preprints.org/manuscript/201710.0192/v1/download is a useful reference on this topic.
Running the included `hashTest.cc` without the hashlib changes, I get 49,580,349 collisions.
The 49,995,000 (i,j) pairs (0 <= i < 10000, i < j < 10000) hash into only 414,651 unique hash values.
We get simple collisions like (0,1) colliding with (2,3).
With the hashlib changes, we get only 707,099 collisions and 49,287,901 unique hash values.
Much better! The `commutative_hash` implementation corresponds to `Sum(4)` in the paper
mentioned above.
`CellTypes::eval()` is more generic but also more limited. `ConstEval::eval()` requires more setup (both in code and at runtime) but has more complete support.
Still unsupported:
- wide muxes (`$_MUX16_` and friends)
Partially supported types have comments in `test_cell.cc`.
Fix `CellTypes::eval() for `$_NMUX_`.
Fix `RTLIL::Cell::fixup_parameters()` for $concat, $bwmux and $bweqx.
Conditionally include help source tracking to preserve ABI.
Docs builds can (and should) use `ENABLE_HELP_SOURCE` so that the generated sphinx docs can perform default grouping and link to source files.
Regular user-builds don't need the source tracking.
`_content` vector owns elements so that when the `ContentListing` is deleted so is the content.
Remove `get_content()` method in favour of `begin()` and `end()` const iterators.
More `const` in general, and iterations over `ContentListing` use `&content` to avoid copying data.
