[llvm-commits] [llvm] r80040 - /llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

[Chris Lattner]

On Aug 25, 2009, at 3:27 PM, Owen Anderson wrote:

> Author: resistor
> Date: Tue Aug 25 17:27:22 2009
> New Revision: 80040
>
> URL: http://llvm.org/viewvc/llvm-project?rev=80040&view=rev
> Log:
> Get rid of this horrible "benign race" by exploiting ManagedStatic  
> to initialize
> the array on its first access.

Thanks Owen, very nice!

-Chris

>
> Modified:
>    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=80040&r1=80039&r2=80040&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Tue Aug 25  
> 17:27:22 2009
> @@ -5014,8 +5014,20 @@
>   AddNodeIDNode(ID, this);
> }
>
> +namespace {
> +  struct EVTArray {
> +    std::vector<EVT> VTs;
> +
> +    EVTArray() {
> +      VTs.reserve(MVT::LAST_VALUETYPE);
> +      for (unsigned i = 0; i < MVT::LAST_VALUETYPE; ++i)
> +        VTs.push_back(MVT((MVT::SimpleValueType)i));
> +    }
> +  };
> +}
> +
> static ManagedStatic<std::set<EVT, EVT::compareRawBits> > EVTs;
> -static EVT VTs[MVT::LAST_VALUETYPE];
> +static ManagedStatic<EVTArray> SimpleVTArray;
> static ManagedStatic<sys::SmartMutex<true> > VTMutex;
>
> /// getValueTypeList - Return a pointer to the specified value type.
> @@ -5025,12 +5037,7 @@
>     sys::SmartScopedLock<true> Lock(*VTMutex);
>     return &(*EVTs->insert(VT).first);
>   } else {
> -    // All writes to this location will have the same value, so  
> it's ok
> -    // to race on it.  We only need to ensure that at least one  
> write has
> -    // succeeded before we return the pointer into the array.
> -    VTs[VT.getSimpleVT().SimpleTy] = VT;
> -    sys::MemoryFence();
> -    return VTs + VT.getSimpleVT().SimpleTy;
> +    return &SimpleVTArray->VTs[VT.getSimpleVT().SimpleTy];
>   }
> }
>
>
>
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