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More heuristics for Combiner-AA. Still catches all important cases, but

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compile time penalty on gnugo, the worst case in MultiSource, is down to
about 2.5% from 30%

llvm-svn: 83824
This commit is contained in:
Nate Begeman 2009-10-12 05:53:58 +00:00
parent 00f4a355eb
commit d27f450262
1 changed files with 19 additions and 6 deletions
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25
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -6230,13 +6230,28 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
// Starting off.
Chains.push_back(OriginalChain);
unsigned Depth = 0;
// Look at each chain and determine if it is an alias. If so, add it to the
// aliases list. If not, then continue up the chain looking for the next
// candidate.
while (!Chains.empty()) {
SDValue Chain = Chains.back();
Chains.pop_back();
// For TokenFactor nodes, look at each operand and only continue up the
// chain until we find two aliases. If we've seen two aliases, assume we'll
// find more and revert to original chain since the xform is unlikely to be
// profitable.
//
// FIXME: The depth check could be made to return the last non-aliasing
// chain we found before we hit a tokenfactor rather than the original
// chain.
if (Depth > 6 || Aliases.size() == 2) {
Aliases.clear();
Aliases.push_back(OriginalChain);
break;
}
// Don't bother if we've been before.
if (!Visited.insert(Chain.getNode()))
@ -6268,8 +6283,7 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
} else {
// Look further up the chain.
Chains.push_back(Chain.getOperand(0));
// Clean up old chain.
AddToWorkList(Chain.getNode());
++Depth;
}
break;
}
@ -6285,8 +6299,7 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
}
for (unsigned n = Chain.getNumOperands(); n;)
Chains.push_back(Chain.getOperand(--n));
// Eliminate the token factor if we can.
AddToWorkList(Chain.getNode());
++Depth;
break;
default:
@ -6312,7 +6325,7 @@ SDValue DAGCombiner::FindBetterChain(SDNode *N, SDValue OldChain) {
// If a single operand then chain to it. We don't need to revisit it.
return Aliases[0];
}
// Construct a custom tailored token factor.
return DAG.getNode(ISD::TokenFactor, N->getDebugLoc(), MVT::Other,
&Aliases[0], Aliases.size());