Copy propagation of special registers - Githubissues

Alamvic / druid

Meta-compiler to generate an optimised JIT compiler frontend based on an Interpreter definition

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Copy propagation of special registers #103

Open guillep opened 8 months ago

guillep commented 8 months ago

Special registers are lowered in the backend and not exposed in during optimization. Thus, they cannot be optimized/propageted and so on.

Example

self MoveR: ReceiverResultReg R: Extra2Reg.
self AddCq: 10 R: Extra2Reg.

=>

self AddCq: 10 R: ReceiverResultReg.

Difficulty: Difficult

Requires some redesigns. Either

lowering the IR, thus reimplementing an extra pass on a lowered version of the IR, and wasting a register (that will be copy propagated) during allocation
or re-introducing the idea of Physical registers in the IR, and thus all passes should take that into account

Moreover, writing to the ReceiverResultReg is tricky because you can only do it when you know you’re not going to fail…