llvm dev - Jul 2006 - [LLVMdev] Inserting move instruction

Dear llvmers,

    I am trying to insert a move instruction where both source and
destination registers are physical registers. How is the code for this?
I tried this one here:

void PhiDeconstruction_Fer::add_move (
                                       MachineFunction & mf,
                                       MachineBasicBlock & mbb,
                                       unsigned src,
                                       unsigned dst
                                     )
{
    MachineBasicBlock::iterator iter = mbb.getFirstTerminator();

    const TargetRegisterClass *rc = mf.getSSARegMap()->getRegClass(dst);

    const MRegisterInfo * reg_info = mf.getTarget().getRegisterInfo();

    reg_info->copyRegToReg(mbb, iter, dst, src, rc);
}

But the getRegClass method seems to expect a virtual register. Could
someone fix this code for me? I could not find an example in the source of
LLVM.

Thank you very much,

Fernando

On Sun, 2 Jul 2006, Fernando Magno Quintao Pereira wrote:
>    MachineBasicBlock::iterator iter = mbb.getFirstTerminator();
>    const TargetRegisterClass *rc = mf.getSSARegMap()->getRegClass(dst);
>    const MRegisterInfo * reg_info = mf.getTarget().getRegisterInfo();
>    reg_info->copyRegToReg(mbb, iter, dst, src, rc);
> }
>
> But the getRegClass method seems to expect a virtual register. Could
> someone fix this code for me? I could not find an example in the source of
> LLVM.
You can't do it with this information.  In some higher context you should 
have information about what register class the physreg is to be 
interpreted as.  Physregs can be in multiple register classes.

All of the register allocators call this method, so there are plenty of 
examples.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/

> On Sun, 2 Jul 2006, Fernando Magno Quintao Pereira wrote:
>
> >    MachineBasicBlock::iterator iter = mbb.getFirstTerminator();
> >    const TargetRegisterClass *rc =
mf.getSSARegMap()->getRegClass(dst);
> >    const MRegisterInfo * reg_info = mf.getTarget().getRegisterInfo();
> >    reg_info->copyRegToReg(mbb, iter, dst, src, rc);
> > }
> >
> > But the getRegClass method seems to expect a virtual register. Could
> > someone fix this code for me? I could not find an example in the
source of
> > LLVM.
>
> You can't do it with this information.  In some higher context you
should
> have information about what register class the physreg is to be
> interpreted as.  Physregs can be in multiple register classes.
>
> All of the register allocators call this method, so there are plenty of
> examples.
>
> -Chris
Thank you, chris. But I still do not understand how to insert this move
instruction :) I have the machine function, the basic block, and the
unsigned descriptors of the source and destiny register. With this
information is possible to insert a move, considering that the source
and destiny are physical registers? The example that I could find, in
the phi-elimination pass, expects virtual registers. But I am eliminating
phi functions after register allocation has been performed. I would like
to know if there is a simple way to discover the class of a physical
register given MachineFunction and MachineBasicBlock. Could you point me
an example in the code of one of the register allocators?

Thanks a lot,

Fernando