[llvm-dev] What's "register pressure set"

[Xing Su via llvm-dev]

Hi everyone,

I'm looking through codes related to registered pressure tracking, mainly the source files 'RegisterPressure.h/cpp', 'MachineRegisterInfo.h/cpp', 'TargetRegisterInfo.h/cpp'. 

There is a concept I can hardly understand, the 'register pressure set'. Class 'TargetRegisterInfo' defines two virtual methods 'getRegClassPressureSets' and 'getRegUnitPressureSets' for querying but I don't see any subclasses overriding it. 

What's the meaning of the register pressure set? Anyone can give me some help?

Thanks!


Xing