[FIRRTL] Reuse XMRRefOps in LowerXMR #8066
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Change the `LowerXMR` pass to reuse previously created `XMRRefOp`s within a module. This is done for later, easier processing of these operations in `LowerToHW`. While these operations could be made to be CSE'd (by giving them the `Pure` trait), it is advantageous to instead not create duplicate operations as this avoids needing to run schedule a mostly useless CSE. This is primarily done to allow for Verilator-compatible lowering of `force_initial` and `release_initial` in `LowerToHW` where it would be useful to know when a force and release are referring to the same reference. (Yes, full alias analysis is necessary to do this correctly and relying on the CSE of `LowerXMR` is going to be buggy.) Signed-off-by: Schuyler Eldridge <[email protected]>
seldridge
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Jan 10, 2025
TaoBi22
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Jul 17, 2025
Change the `LowerXMR` pass to reuse previously created `XMRRefOp`s within a module. This is done for later, easier processing of these operations in `LowerToHW`. While these operations could be made to be CSE'd (by giving them the `Pure` trait), it is advantageous to instead not create duplicate operations as this avoids needing to run schedule a mostly useless CSE. This is primarily done to allow for Verilator-compatible lowering of `force_initial` and `release_initial` in `LowerToHW` where it would be useful to know when a force and release are referring to the same reference. (Yes, full alias analysis is necessary to do this correctly and relying on the CSE of `LowerXMR` is going to be buggy.) Signed-off-by: Schuyler Eldridge <[email protected]>
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Change the
LowerXMRpass to reuse previously createdXMRRefOps within a module. This is done for later, easier processing of these operations inLowerToHW. While these operations could be made to be CSE'd (by giving them thePuretrait), it is advantageous to instead not create duplicate operations as this avoids needing to run schedule a mostly useless CSE.This is primarily done to allow for Verilator-compatible lowering of
force_initialandrelease_initialinLowerToHWwhere it would be useful to know when a force and release are referring to the same reference. (Yes, full alias analysis is necessary to do this correctly and relying on the CSE ofLowerXMRis going to be buggy.)