[llvm-dev] callee saved regs list

[Krzysztof Parzyszek via llvm-dev]

On 8/17/2017 5:07 AM, Jonas Paulsson via llvm-dev wrote:
> It seems strange that the common code cannot deduce for itself that the 
> super regs are also callee saved given that all sub-regs of a register are.

For this to be true, the super-register needs to be covered by its 
sub-registers.  This is not the case in general (e.g. X86).  Also, if 
you have a multi-level sub-register hierarchy then you may not need all 
sub-registers to cover a given register.

Out of the users of the callee-saved information, LivePhysRegs should 
handle the liveness properly.

-Krzysztof

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