[llvm-dev] Misuse of MRI.getRegClass in multiple target's FastIsel code

Krzysztof Parzyszek via llvm-dev llvm-dev at lists.llvm.org
Fri Sep 23 08:30:01 PDT 2016

MachineRegisterInfo::getRegClass does take a virtual register and 
returns the TargetRegisterClass of that register. You're thinking about 


On 9/23/2016 10:20 AM, Craig Topper via llvm-dev wrote:
> This code or subtle variations of it appears in multiple targets. It
> tries to convert from a register to a register class using getRegClass,
> but getRegClass is really supposed to take a register class enum value
> and get the register class object for it. It doesn't convert a register
> to a class. In fact there's not always a single or canonical class for a
> given register.
> What is the right way to do this?
>     unsigned SrcReg = Reg + VA.getValNo();
>     unsigned DestReg = VA.getLocReg();
>     // Avoid a cross-class copy. This is very unlikely.
>     if (!MRI.getRegClass(SrcReg)->contains(DestReg))
>       return false;
> ~Craig
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