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

[Eric Christopher via llvm-commits]

On Thu, Nov 19, 2015 at 4:50 PM Dan Gohman <sunfish at mozilla.com> wrote:

> 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.
>

Hrm. That's what I thought you were going to say. Frustrating. :)

-eric


>
> Dan
>
>
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