Currently we assign a (new) virtual register to instructions without any defs, it's used as instruction id. This can be convenient sometimes, but the problem is that regalloc has to iterate over all virtual registers a number of times (and it allocates some memory for each virtual register).
We should try changing this so that virtual registers are only used for actual defs or temps, and see if it helps 3d-cube and audio-beat-detection.
Created attachment 610867 [details] [diff] [review]
The patch moves the LSRA movegroups from VirtualRegister to a new class, InstructionData. This was necessary and it simplifies LSRA a bit: an instruction can have multiple virtual registers so associating movegroups with instructions is more natural. It also allows us to remove one of the three movegroups.
Number of virtual registers for the same function, before/after:
3d-cube : 2032 -> 1318
beat-detection: 3806 -> 2089
3d-cube : 1710 -> 996
beat-detection: 3207 -> 1494
Small performance win and should use less memory.
Thanks for the quick review!