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

[Eric Christopher via llvm-commits]

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?

-eric


>
> Dan
>
>
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