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When a lot of combinational logic is driven from top level inputs, work can be wasted evaluating that logic if the top level inputs don't change. This change adds an optimization by performing a change detect on the top level inputs, and evaluate 'ico' logic only if the top level input actually changed. This especially helps with --hierarchical/--lib-create which runs the 'ico' of each sub-model in the eval settle loop. This was observed to yield 40%+ run-time speedup on some partitioned designs. The added change detection is cheap, so it is emitted even if the 'ico' region is small, and is on by default. The optimization is only sound if the model itself does not write to the top level inputs (otherwise the 'previous value' variables would be out of sync, which are not updated by internal writes.). If we can detect a top level input is written within the design, then for that input, we fall back on always running the relevant logic. With --vpi we cannot prove safety statically, so --vpi will disable this optimisation unless explicitly enabled. (In which case it's the user's responsibility to not write to top level inputs via the VPI.) |
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| bin | ||
| gen | ||
| guide | ||
| .gitignore | ||
| CONTRIBUTING.rst | ||
| CONTRIBUTORS | ||
| Makefile | ||
| README.rst | ||
| internals.rst | ||
| security.rst | ||
| spelling.txt | ||
| verilated.dox | ||
README.rst
.. SPDX-FileCopyrightText: 2003-2026 Wilson Snyder .. SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0 Verilator Documentation ======================= This folder contains sources for Verilator documentation. For formatted documentation see: - `Verilator README <https://github.com/verilator/verilator>`_ - `Verilator installation and package directory structure <https://verilator.org/install>`_ - `Verilator manual (HTML) <https://verilator.org/verilator_doc.html>`_, or `Verilator manual (PDF) <https://verilator.org/verilator_doc.pdf>`_ - `Subscribe to Verilator announcements <https://github.com/verilator/verilator-announce>`_ - `Verilator forum <https://verilator.org/forum>`_ - `Verilator issues <https://verilator.org/issues>`_