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Do not try and sink a load whose chain result has more than one use, when 

trying to create RMW opportunities in the x86 backend.  This can cause a 
cycle to appear in the graph, since the other uses may eventually feed into
the TokenFactor we are sinking the load below.

llvm-svn: 81996
This commit is contained in:
Nate Begeman 2009-09-16 03:20:46 +00:00
parent 771a1f1720
commit 1ae49ee7ca
1 changed files with 5 additions and 2 deletions
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7
llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
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@ -364,7 +364,9 @@ static void MoveBelowTokenFactor(SelectionDAG *CurDAG, SDValue Load,
Store.getOperand(2), Store.getOperand(3)); Store.getOperand(2), Store.getOperand(3));
} }
/// isRMWLoad - Return true if N is a load that's part of RMW sub-DAG. /// isRMWLoad - Return true if N is a load that's part of RMW sub-DAG. The
/// chain produced by the load must only be used by the store's chain operand,
/// otherwise this may produce a cycle in the DAG.
/// ///
static bool isRMWLoad(SDValue N, SDValue Chain, SDValue Address, static bool isRMWLoad(SDValue N, SDValue Chain, SDValue Address,
SDValue &Load) { SDValue &Load) {
@ -382,8 +384,9 @@ static bool isRMWLoad(SDValue N, SDValue Chain, SDValue Address,
return false; return false;
if (N.hasOneUse() && if (N.hasOneUse() &&
LD->hasNUsesOfValue(1, 1) &&
N.getOperand(1) == Address && N.getOperand(1) == Address &&
N.getNode()->isOperandOf(Chain.getNode())) { LD->isOperandOf(Chain.getNode())) {
Load = N; Load = N;
return true; return true;
} }