This adds a native json based witness trace format. By having a common
format that includes everything we support, and providing a conversion
utility (yosys-witness) we no longer need to implement every format for
every tool that deals with witness traces, avoiding a quadratic
opportunity to introduce subtle bugs.
Included:
* smt2: New yosys-smt2-witness info lines containing full hierarchical
paths without lossy escaping.
* yosys-smtbmc --dump-yw trace.yw: Dump results in the new format.
* yosys-smtbmc --yw trace.yw: Read new format as constraints.
* yosys-witness: New tool to convert witness formats.
Currently this can only display traces in a human-readable-only
format and do a passthrough read/write of the new format.
* ywio.py: Small python lib for reading and writing the new format.
Used by yosys-smtbmc and yosys-witness to avoid duplication.
genrtlil.cc and simplify.cc had inconsistent and slightly broken
handling of signedness for array querying functions. These functions are
defined to return a signed result. Simplify always produced an unsigned
and genrtlil always a signed 32-bit result ignoring the context.
Includes tests for the the relvant edge cases for context dependent
conversions.
The previously generated logic assumed an unconstrained past value in
the initial state and did not handle 'x values. While the current formal
verification flow uses 2-valued logic, SVA value change expressions
require a past value of 'x during the initial state to behave in the
expected way (i.e. to consider both an initial 0 and an initial 1 as
$changed and an initial 1 as $rose and an initial 0 as $fell).
This patch now generates logic that at the same time
a) provides the expected behavior in a 2-valued logic setting, not
depending on any dont-care optimizations, and
b) properly handles 'x values in yosys simulation
For SVAs that have an explicit clock and are contained in a procedure
which conditionally executes the assertion, verific expresses this using
a mux with one input connected to constant 1 and the other output
connected to an SVA_AT. The existing code only handled the case where
the first input is connected to 1. This patch also handles the other
case.
The `-keepdc` option prevents merging flipflops with dont-care bits in
their initial value, as, in general, this is not a valid transform for
formal verification.
The keepdc option of `opt` is passed along to `opt_merge` now.
