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

[Craig Topper via llvm-dev]

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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