[llvm-dev] Problem of getting two unused registers in eliminateFrameIndex()

[Ehsan Ali via llvm-dev]

Your hint was very helpful.

I enabled "requiresFrameIndexScavenging" and the
createVirtualRegister() worked as expected:

bool LaserRegisterInfo::
requiresFrameIndexScavenging(const MachineFunction &MF) const {
  return true;
}

I don't understand the logic behind it but somehow they are related.

Thank you Krzysztof.

Ehsan Ali.

On 8/15/17, Krzysztof Parzyszek via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> There isn't really much else that you can do here. If you anticipate
> that two extra registers will be needed at some particular point in the
> function, reserve two spill slots.
>
> Creating virtual registers in replaceFrameIndex should work, but make
> sure that your target implements "requiresRegisterScavenging",
> "requiresFrameIndexScavenging",
> "requiresFrameIndexReplacementScavenging" (all from TargetRegisterInfo)
> as appropriate.
>
> -Krzysztof
>
> On 8/14/2017 8:39 PM, Ehsan Ali via llvm-dev wrote:
>> Hello all,
>>
>> For my custom processor backend I am trying add some instruction using
>> BuildMI() inside eliminateFrameIndex().
>>
>> I tried RegScavenger like this:
>>
>> unsigned RegUnused0 = RS->FindUnusedReg(&LASER::GNPRegsRegClass);
>> if (!RegUnused0)
>>    RegUnused0 = RS->scavengeRegister(&LASER::GNPRegsRegClass, II, SPAdj);
>> assert(RegUnused0 && "Register scavenger failed");
>> RS->setRegUsed(RegUnused0);
>>
>> It works but there are two issues:
>>
>> 1) I need to registers and RegScavenger only returns one.
>> 2) I cannot unset the used register and I get spill slot error message
>> when I ran out of the available registers.
>>
>> So I gave up and tried createVirtualRegister():
>>
>> MachineRegisterInfo &RegInfo = MBB.getParent()->getRegInfo();
>> const TargetRegisterClass *RC = &LASER::GNPRegsRegClass;
>> unsigned Reg = RegInfo.createVirtualRegister(RC);
>>
>> But then I get the following error:
>>
>> MachineCopyPropagation.cpp:267: void
>> anonymous}::MachineCopyPropagation::CopyPropagateBlock(llvm::MachineBasicBlock&):
>> Assertion `!TargetRegisterInfo::isVirtualRegister(Reg) &&
>> "MachineCopyPropagation should be run after register allocation!"'
>> failed.
>>
>> How can I solve my problem of getting two free registers in
>> eliminateFrameIndex() ?
>>
>> Thank you,
>> Ehsan Ali.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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