[llvm] r253465 - [WebAssembly] Enable register coloring and register stackifying.

[Dan Gohman via llvm-commits]

On Thu, Nov 19, 2015 at 4:33 PM, Eric Christopher <echristo at gmail.com>
wrote:

>
>
> On Thu, Nov 19, 2015 at 4:32 PM Dan Gohman <sunfish at mozilla.com> wrote:
>
>> On Thu, Nov 19, 2015 at 2:38 PM, Eric Christopher <echristo at gmail.com>
>> wrote:
>>
>>>
>>>
>>>> +  // FIXME: If scheduling has moved an ARGUMENT virtual register, move
>>>> it back,
>>>> +  // and recompute liveness. This is a temporary hack.
>>>> +  bool SawNonArg = false;
>>>> +  bool MovedArg = false;
>>>> +  MachineBasicBlock &EntryMBB = MF.front();
>>>> +  for (auto MII = EntryMBB.begin(); MII != EntryMBB.end(); ) {
>>>> +    MachineInstr *MI = &*MII++;
>>>> +    if (MI->getOpcode() == WebAssembly::ARGUMENT_I32 ||
>>>> +        MI->getOpcode() == WebAssembly::ARGUMENT_I64 ||
>>>> +        MI->getOpcode() == WebAssembly::ARGUMENT_F32 ||
>>>> +        MI->getOpcode() == WebAssembly::ARGUMENT_F64) {
>>>> +      EntryMBB.insert(EntryMBB.begin(), MI->removeFromParent());
>>>> +      if (SawNonArg)
>>>> +        MovedArg = true;
>>>> +    } else {
>>>> +      SawNonArg = true;
>>>> +    }
>>>> +  }
>>>> +  if (MovedArg) {
>>>> +    SlotIndexes &Slots = getAnalysis<SlotIndexes>();
>>>> +    Liveness->releaseMemory();
>>>> +    Slots.releaseMemory();
>>>> +    Slots.runOnMachineFunction(MF);
>>>> +    Liveness->runOnMachineFunction(MF);
>>>> +  }
>>>>
>>>>
>>> How temporary is this and do you plan on making the arguments
>>> non-schedulable? (Which is arguably what should be happening right? They
>>> should be the equivalent to an alloca yes?)
>>>
>>
>> I already wrote code to replace it: http://reviews.llvm.org/D14750 . If
>> that patch isn't accepted, I'll go back to the drawing board to find some
>> other way to pin the instructions to the top of the block. I don't yet have
>> an idea for doing this, but it would be a high priority to find one.
>>
>
> Makes sense. I'm curious on the difference between this and using an
> alloca to do the same work?
>

An alloca would translate into a FrameIndex operand, but we really want it
to act like a virtual register so that we can compute its liveness using
LiveIntervals and color it along with the other registers.

Dan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20151119/35a95f53/attachment.html>