[LLVMdev] VirtRegMap Error

[Evan Cheng]

On May 8, 2008, at 11:36 AM, David Greene wrote:

> I just updated from upstream llvm as of about last Thursday and I'm
> getting a segfault in VirtRegMap::RemoveMachineInstrFromMaps.
> It seems that the particular instruction being removed happens
> to reference an object at stack slot 4.  The first spilled register is
> assigned stack slot 6 so LowSpillSlot == 6.  Then, when we try to
> erase from SpillSlotToUsesMap, we index with a negative number.
>
> The instruction being removed is generated by instruction selection,
> so it is part of the original program:
>
> %reg1309<def> = FsMOVLPDrm <fi#4>, 1, %reg0, 0, Mem:LD(8,8) [ZETA + 0]
>
> Since we're hooking up llvm to custom code, I want to check  
> assumptions.
> Is there anything in llvm-gcc or the other llvm tools that could  
> generate a
> stack slot reference like this before register allocation?   
> Basically, I'm

Codegen can definitely create stack slots during isel lowering. I  
don't think you can assume all non-fixed slots are created during  
register allocation.

Evan

>
> trying to see if only our code could ever do this.  Otherwise, we  
> have a bug
> in llvm.  Is everything on the stack assumed to be mem2reg'd and so  
> this
> never happens with llvm tools?
>
> Thanks.
>
>                                                -Dave
>
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