[llvm-dev] InstrEmitter::CreateVirtualRegisters handling of CopyToReg

[Jonas Paulsson via llvm-dev]

Hi Alex,

nice to hear that this is of use to you!

Feel free to post it on Phabricator, and please put Ulrich Weigand as 
reviewer and author. I would like to be subscriber...

Thank you,

Jonas


On 2018-07-30 16:58, Alexey Zhikhartsev wrote:
> Hi Jonas,
>
> This patch helps with a problem on our out-of-tree backend; we would 
> love to get some feedback about this patch from the community and 
> potentially upstream it. Would you mind submitting this patch to 
> phabricator? I understand that you might be busy; if so, I could 
> submit it myself (and give credit to you, of course). Thanks!
>
> Best,
> Alex
>
>
> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org 
> <mailto:llvm-dev-bounces at lists.llvm.org>] On Behalf Of Jonas Paulsson 
> via llvm-dev
> Sent: Wednesday, May 30, 2018 9:03 AM
> To: llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
> Cc: Ulrich Weigand <ulrich.weigand at de.ibm.com 
> <mailto:ulrich.weigand at de.ibm.com>>
> Subject: [llvm-dev] InstrEmitter::CreateVirtualRegisters handling of 
> CopyToReg
>
> Hi,
>
> I wonder if anyone has any comment on a patch like:
>
> diff --git a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> index 65ee3816f84..4780f6f0e59 100644
> --- a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> +++ b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> @@ -243,18 +243,21 @@ void InstrEmitter::CreateVirtualRegisters(SDNode
> *Node,
>
>       if (!VRBase && !IsClone && !IsCloned)
>         for (SDNode *User : Node->uses()) {
>           if (User->getOpcode() == ISD::CopyToReg &&
>               User->getOperand(2).getNode() == Node &&
>               User->getOperand(2).getResNo() == i) {
>             unsigned Reg =
> cast<RegisterSDNode>(User->getOperand(1))->getReg();
>             if (TargetRegisterInfo::isVirtualRegister(Reg)) {
> -            const TargetRegisterClass *RegRC = MRI->getRegClass(Reg);
> -            if (RegRC == RC) {
> +            // Allow constraining the virtual register's class within
> reason,
> +            // just like what AddRegisterOperand will allow.
> +            const TargetRegisterClass *ConstrainedRC
> +              = MRI->constrainRegClass(Reg, RC, MinRCSize);
> +            if (ConstrainedRC) {
>                 VRBase = Reg;
>                 MIB.addReg(VRBase, RegState::Define);
>                 break;
>               }
>             }
>           }
>         }
>
> Why do the register classes currently have to match exactly in this case?
>
> It seems that these COPYs that now remain may end up in the same 
> register class, if the users require it. So why not constrain also 
> here directly, if this is done generally when the register is used as 
> input?
>
> /Jonas
>
>
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