llvm dev - Dec 2018 - New to LLVM. Need help getting available register

Hi,
I'm new to LLVM. I'd like to know if there is a method I can call
whenever I need any available CPU register.
Thanks.
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m m via llvm-dev <llvm-dev at lists.llvm.org> writes:
> I'm new to LLVM. I'd like to know if there is a method I can call
> whenever I need any available CPU register.
Take a look at RegisterScavenging.  Of course, this only works after
register allocation.  Before register allocation you'd just create a new
virtual register.

                              -David

Is it possible to get a virtual register and then use that to create a real
register? I've seen it done in unittests/CodeGen/MachineInstrTest.cpp like
this:

unsigned VirtualDef1 = -42;
  VD1VU->addOperand(*MF,
                    MachineOperand::CreateReg(VirtualDef1, /*isDef*/ true));


But when I do that in my code I get an assertion so I wasn't sure if
it's legal or not.
Thanks.

________________________________
From: David Greene <dag at cray.com>
Sent: Wednesday, January 2, 2019 9:23 AM
To: m m
Cc: via llvm-dev
Subject: Re: [llvm-dev] New to LLVM. Need help getting available register

m m via llvm-dev <llvm-dev at lists.llvm.org> writes:
> I'm new to LLVM. I'd like to know if there is a method I can call
> whenever I need any available CPU register.
Take a look at RegisterScavenging.  Of course, this only works after
register allocation.  Before register allocation you'd just create a new
virtual register.

                              -David
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