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Check call has one predecessor before considering eliminating guard #6619

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Merged
jdmpapin merged 1 commit into from
Aug 8, 2022
Merged

Check call has one predecessor before considering eliminating guard #6619

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22 changes: 21 additions & 1 deletion compiler/optimizer/VPHandlers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9460,7 +9460,27 @@ static TR::Node *constrainIfcmpeqne(OMR::ValuePropagation *vp, TR::Node *node, b
if (callNode &&
callNode->getOpCode().isCall())
{
virtualGuardWillBeEliminated = canFoldNonOverriddenGuard(vp, callNode, node);
// Calling canFoldNonOverriddenGuard has the potential side effect of creating global
// constraints for definitions used by the call that reach the conditional branch that is
// under consideration, without taking into account definitions that might reach the call
// on other paths. In order to decide correctly whether the guard can be eliminated and
// ensure any global constraints will be created correctly, this needs to check that the
// only path to the call must pass through the current branch. The easiest way to do
// that is to check that the target of the branch is the call block itself and that the
// call block has no other predecessors, though that will fail to optimize any case where
// the call is reached by a sequence of branches from the target of the branch, each of
// which has a single predecessor.
//
if (target->getPredecessors().size() == 1)
{
TR::Block *callBlock = node->getVirtualCallTreeForGuard()->getEnclosingBlock();

if (callBlock == target)
{
virtualGuardWillBeEliminated = canFoldNonOverriddenGuard(vp, callNode, node);
}
}

if (!virtualGuardWillBeEliminated &&
vp->lastTimeThrough() &&
vp->_isGlobalPropagation)
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