Extend two existing opt passes and add one new pass to collapse
serial/dynamic-index structures that were leaving high logic depth:
- opt_first_fit_alloc: recognize the "coalesce-matrix" first-fit
allocator variant (same_cat[i][k] coalescing gated on the leader's
enable, driven from a raw input enable). Rewrite both the lane_slot
allocation and the xbar field gather from one shared log-depth scan.
- opt_prienc: detect round-robin / rotated-priority scans (req scanned
from idx_last downward with wraparound) and rewrite the depth-N
idx--/req[idx] mux chain to rotate -> log-depth priority-encode ->
unrotate.
- opt_priokey (new): recognize priority-by-key one-hot accumulators and
replace each dynamic taken[key] read ($shiftx/$bmux) with the
equivalent pairwise-key-compare reduction, dropping the wide dynamic
indexing. Supports -strict for full-key-range formal validation.
Each includes self-contained tests (equiv_opt / sat -prove-asserts,
mux-bound and negative cases) in tests/opt/.
Co-authored-by: Cursor <cursoragent@cursor.com>
These updates should not be necessary. In fact, if they were necessary, this code
would be buggy, because the results would depend on the order in which wires are traversed:
If wire A is retained, which causes an update to `used_signals`, which then causes wire B
to be retained when it otherwise wouldn't be, then we would get different results depending
on whether A is visited before B.
These updates will also make it difficult to process these wires in parallel.
This pass converts cascaded chains of arithmetic and logic cells ($add,
$mul, $and, $or, $xor) into balanced binary trees to improve timing
performance in hardware synthesis.
The optimization uses a breadth-first search approach to identify chains
of compatible cells, then recursively constructs balanced trees that
reduce the critical path depth.
Features:
- Supports arithmetic cells: $add, $mul
- Supports logic cells: $and, $or, $xor
- Command-line options: -arith (arithmetic only), -logic (logic only)
- Preserves signed/unsigned semantics
- Comprehensive test suite with 30 test cases
Original implementation by Akash Levy <akash@silimate.com> for Silimate.
Upstreamed from https://github.com/Silimate/yosys
