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Prevent hoisting nodes with order side effects #100160

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Mar 26, 2024
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Prevent hoisting nodes with order side effects #100160

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13 changes: 11 additions & 2 deletions src/coreclr/jit/optimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4596,6 +4596,15 @@ void Compiler::optHoistLoopBlocks(FlowGraphNaturalLoop* loop,
// hence this check is not present in optIsCSEcandidate().
return true;
}
else if ((node->gtFlags & GTF_ORDER_SIDEEFF) != 0)
{
// If a node has an order side effect, we can't hoist it at all: we don't know what the order
// dependence actually is. For example, assertion prop might have determined a node can't throw
// an exception, and eliminated the GTF_EXCEPT flag, replacing it with GTF_ORDER_SIDEEFF. We
// can't hoist because we might then hoist above the expression that led assertion prop to make
// that decision. This can happen in JitOptRepeat, where hoisting can follow assertion prop.
return false;
}

// Tree must be a suitable CSE candidate for us to be able to hoist it.
return m_compiler->optIsCSEcandidate(node);
Expand Down Expand Up @@ -4786,7 +4795,7 @@ void Compiler::optHoistLoopBlocks(FlowGraphNaturalLoop* loop,
}
else if (!top.m_hoistable)
{
top.m_failReason = "not handled by cse";
top.m_failReason = "not handled by hoisting or CSE";
}
#endif

Expand Down Expand Up @@ -4869,7 +4878,7 @@ void Compiler::optHoistLoopBlocks(FlowGraphNaturalLoop* loop,
treeIsHoistable = IsNodeHoistable(tree);
if (!treeIsHoistable)
{
INDEBUG(failReason = "not handled by cse";)
INDEBUG(failReason = "not handled by hoisting or CSE";)
}
}

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