[LLVMdev] MachineOperand: Subreg defines and the Undef flag (original) (raw)

Jakob Stoklund Olesen stoklund at 2pi.dk
Thu Jul 5 09:21:26 PDT 2012

On Jul 5, 2012, at 8:53 AM, "Pranav Bhandarkar" <pranavb at codeaurora.org> wrote:

Hi Jakob,

Thanks for your reply.

The flag goes on NewMI1 because the virtual register B isn't live before that instruction. But you probably shouldn't be doing this yourself. Your NewMI code isn't in SSA form because B has multiple definitions. Just use a REGSEQUENCE instruction, and let the register allocator do the transformation for you. Aaargh. So you mean something like this ? NewMI1:: Vreg1 = 0 ; Vreg1 and Vreg2 are 32 bit virt. regs. NewMI2:: Vreg2 = COPY C:losubreg. NewMI3:: B= REGSEQUENCE<Vreg1, hisubreg, Vreg2, losubreg> ; B is a 64 bit virt reg.

Yes.

For this particular case, you can also use INSERT_SUBREG. That might be simpler.

/jakob

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