[PATCH] LivePhysRegs: Add support to add pristine registers when populating with live-in/live-out registers.

Matthias Braun matze at braunis.de
Fri May 29 16:01:45 PDT 2015

In http://reviews.llvm.org/D10139#181314, @qcolombet wrote:

> Hi Matthias,
> I miss something.
>  Why do we need to account for the pristine registers?

Before prologue/epilogue insertion we don't need to account for them. All current users for LivePhysRegs are before prologue/epilogue insertion so they won't need this (by default AddPristineRegs is false).

After prologue/epilogue insertion those registers are live, you cannot use them for temporary values or place an instruction that would clobber them. Now you can either include them in the set of live registers compute by this class, the alternative is that each time you ask LivePhysReg whether something is alive and you get a negative answer that it may be pristine registers and alive anyway. I decided that it less error prone to simply include the pristine registers in the live registers list.




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