Commit c8e0ac0 introduces a regression on handling case exprs that look
like sva labels. After some debugging, we shouldn't push the identifier
ast node to the ast_stack, otherwise, we will get the following
assertion failure:
```
➜ /tmp yosys -p 'read -sv a1.v'
/----------------------------------------------------------------------------\
| yosys -- Yosys Open SYnthesis Suite |
| Copyright (C) 2012 - 2025 Claire Xenia Wolf <claire@yosyshq.com> |
| Distributed under an ISC-like license, type "license" to see terms |
\----------------------------------------------------------------------------/
Yosys 0.57+1 (git sha1 baa61a146, clang++ 20.1.8 -fPIC -O3)
-- Running command `read -sv a1.v' --
1. Executing Verilog-2005 frontend: a1.v
Parsing SystemVerilog input from `a1.v' to AST representation.
ERROR: Assert `extra->ast_stack.size() == 1' failed in frontends/verilog/verilog_parser.y:709.
➜ /tmp cat a1.v
module test(input wire A);
localparam TEST = 1;
always_comb begin
case (A)
TEST: assert(1);
endcase
end
endmodule
```
We encountered this issue before but with a different error message[^1],
[^1]: https://github.com/YosysHQ/yosys/issues/862
We're currently on version 3.6 of bison at Google, and Yosys
still correctly builds with it. This should better reflect
the actual requirements rather than an overly restrictive
check. If features from 3.8 are required it seems like bumping
would be appropriate.
Signed-off-by: Ethan Mahintorabi <ethanmoon@google.com>
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.
