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isphysregused
2013 Jan 27
1
[LLVMdev] Clarification about callee saved regs and MachineRegisterInfo::isPhyRegUsed
Hi,
I am confused about the call to isPhyRegUsed in
calculateCalleeSavedRegisters:
if (Fn.getRegInfo().isPhysRegUsed(Reg))
{
// If the reg is modified, save it!
CSI.push_back(CalleeSavedInfo(Reg));
}
It seems that isPhyRegUsed
returns true if the register is read or written in the function.
If
this is right, why do we save a register if...