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757cbb3c80
Before this commit, any wire that was not driven by an output port of exactly one comb cell would not be localized, even if there were no feedback arcs through that wire. This would cause the wire to become buffered and require (often quite a few) extraneous delta cycles during evaluation. To alleviate this problem, -O5 was running `splitnets -driver`. However, this solution was mistaken. Because `splitnets -driver` followed by `opt_clean -purge` would produce more nets with multiple drivers, it would have to be iterated to fixpoint. Moreover, even if this was done, it would not be sufficient because `opt_clean -purge` does not currently remove wires with the `\init` attribute (and it is not desirable to remove such wires, since they correspond to registers and may be useful for debugging). The proper solution is to consider the condition in which a wire may be localized. Specifically, if there are no feedback arcs through this wire, and no part of the wire is driven by an output of a sync cell, then the wire holds no state and is localizable. After this commit, the original condition for not localizing a wire is replaced by a check for any sync cell driving it. This makes it unnecessary to run `splitnets -driver` in the majority of cases to get a design with no buffered wires, and -O5 no longer includes that pass. As a result, Minerva SRAM SoC no longer has any buffered wires, and runs ~27% faster. In addition, this commit prepares the flow graph for introduction of sync outputs of black boxes. Co-authored-by: Jean-François Nguyen <jf@lambdaconcept.com> |
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| btor | ||
| cxxrtl | ||
| edif | ||
| firrtl | ||
| ilang | ||
| intersynth | ||
| json | ||
| protobuf | ||
| simplec | ||
| smt2 | ||
| smv | ||
| spice | ||
| table | ||
| verilog | ||