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Ease contention on this lock by noticing that all writes to the VTs array will

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be of (dynamically) constant values, so races on it are immaterial.  We just need
to ensure that at least one write has completed before return the pointer into it.

With this change, parllc exhibits essentially no overhead on 403.gcc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79708 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2009-08-22 00:29:12 +00:00
parent d99dda22f4
commit 0b7401d3cd
1 changed files with 5 additions and 2 deletions
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7
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -5022,12 +5022,15 @@ static ManagedStatic<sys::SmartMutex<true> > VTMutex;
/// getValueTypeList - Return a pointer to the specified value type.
///
const EVT *SDNode::getValueTypeList(EVT VT) {
sys::SmartScopedLock<true> Lock(*VTMutex);
if (VT.isExtended()) {
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;
return &VTs[VT.getSimpleVT().SimpleTy];
sys::MemoryFence();
return VTs + VT.getSimpleVT().SimpleTy;
}
}