Avoid creating def-use constraints for nodes which are dead after synthesis.#3810
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Avoid creating def-use constraints for nodes which are dead after synthesis.#3810copybara-service[bot] wants to merge 1 commit intomainfrom
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…thesis. Dead-after-synthesis nodes (ie nodes which are ultimately only visible from trace, cover or assert nodes) are modeled as having zero delay since synthesis tools will be able to recognize their computation plays no part in the ultimate chip design and so can be ignored. Unfortunately we were still scheduling these nodes as normal (albeit with zero delay). This works but can cause scaling issues due to the addition of (trivial) constraints. By instead excluding these from the constraint model and instead doing the trivial scheduling as a final fixup step the schedulers performance can be drastically improved. We have seen as codegen times fall by more than half on some designs. PiperOrigin-RevId: 866633719
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Avoid creating def-use constraints for nodes which are dead after synthesis.
Dead-after-synthesis nodes (ie nodes which are ultimately only visible from trace, cover or assert nodes) are modeled as having zero delay since synthesis tools will be able to recognize their computation plays no part in the ultimate chip design and so can be ignored. Unfortunately we were still scheduling these nodes as normal (albeit with zero delay). This works but can cause scaling issues due to the addition of (trivial) constraints. By instead excluding these from the constraint model and instead doing the trivial scheduling as a final fixup step the schedulers performance can be drastically improved.
We have seen as codegen times fall by more than half on some designs.