[FIRRTL] InferResets: properly lower FART'd registers #7680
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This is quick fix for llvm#7675. The way this is supposed to work is, FRT is not supposed to add a reset if a register already has one, but it isn't smart enough to understand that an invalid value corresponds to a register without a reset. As a result, it will not add a reset to this register. Later on, in SFCCompat, when choosing how to lower the Invalid value, it should "see" that the registers should all have a reset, by looking for the FRT annotation, and choose to lower the reset value to 0 or remove the reset accordingly. The "bug" is that the FRT annotation on a parent module won't be discovered on the child module. This attaches the annotation on to every module in a reset domain, so that it can be found.
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This is quick fix for #7675.
The way this is supposed to work is, FRT is not supposed to add a reset if a register already has one, but it isn't smart enough to understand that an invalid value corresponds to a register without a reset. As a result, it will not add a reset to this register. Later on, in SFCCompat, when choosing how to lower the Invalid value, it should "see" that the registers should all have a reset, by looking for the FRT annotation, and choose to lower the reset value to 0 or remove the reset accordingly. The "bug" is that the FRT annotation on a parent module won't be discovered on the child module.
This attaches the annotation on to every module in a reset domain, so that it can be found.