mirror of https://github.com/llvm/circt.git
0d8106e640
Extend the Mem2Reg pass to support drives to `llhd.sig.array_get`
projections into a promotable signal. This requires a few changes:
- When checking whether a signal is promotable, we have to recursively
check its users and look through `llhd.sig.array_get` ops to see if
all uses are safe for promotion.
- The lattice used to propagate needed and reaching definitions has to
track the projection being driven separately from the underlying root
slot being driven.
- A new set of helpers to unpack and pack stacks of projections help
probes and drives take a promotable slot and its value, descend into
subfields as indicated by a set of projection ops ("unpack"), and then
optionally mutate the value of a subfield and zip the updated value
back up to the promotable slot ("pack").
- During backward and forward propagation across the lattice, drives to
projections have to create the need for a definition of the slot to be
available because they have to take the slot's current value in order
to mutate the projected field.
- The functions that resolve definitions have to unpack a slot's value
according to the projections between the probe and the slot. In case
of a drive they also have to mutate the projected field value after
unpacking and then pack everything back op in order to create a new
reaching definition for the entire slot to be forwarded to readers.
This commit also drops `slotOrder` in favor of a `promotable` set of
values. The actual order of slots was never used.
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