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Skip allocation for ZeroInit writeThru intervals #58677

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Merged
merged 3 commits into from
Sep 7, 2021
Merged

Skip allocation for ZeroInit writeThru intervals #58677

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61f713e
Do not allocate register if ZeroInit/EHWriteThru
kunalspathak Sep 4, 2021
64c8cc9
Update the comments about zero-init heuristics
kunalspathak Sep 4, 2021
e6f0ae8
jit format
kunalspathak Sep 6, 2021
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6 changes: 4 additions & 2 deletions src/coreclr/jit/lclvars.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4142,8 +4142,10 @@ void Compiler::lvaMarkLclRefs(GenTree* tree, BasicBlock* block, Statement* stmt,
{
bool bbInALoop = (block->bbFlags & BBF_BACKWARD_JUMP) != 0;
bool bbIsReturn = block->bbJumpKind == BBJ_RETURN;
// TODO: Zero-inits in LSRA are created with below condition. Try to use similar condition here as well.
// if (compiler->info.compInitMem || varTypeIsGC(varDsc->TypeGet()))
// TODO: Zero-inits in LSRA are created with below condition. But if filter out based on that condition
// we filter lot of interesting variables that would benefit otherwise with EH var enregistration.
// bool needsExplicitZeroInit = !varDsc->lvIsParam && (info.compInitMem ||
// varTypeIsGC(varDsc->TypeGet()));
bool needsExplicitZeroInit = fgVarNeedsExplicitZeroInit(lclNum, bbInALoop, bbIsReturn);

if (varDsc->lvSingleDefRegCandidate || needsExplicitZeroInit)
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7 changes: 7 additions & 0 deletions src/coreclr/jit/lsra.cpp
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Expand Up @@ -4945,6 +4945,13 @@ void LinearScan::allocateRegisters()
// it to a different register file.
allocate = false;
}
else if ((currentInterval->isWriteThru) && (refType == RefTypeZeroInit))
{
// For RefTypeZeroInit which is a write thru, there is no need to allocate register
// right away. It can be assigned when actually definition occurs.
// In future, see if avoiding allocation for RefTypeZeroInit gives any benefit in general.
allocate = false;
}
if (!allocate)
{
INDEBUG(dumpLsraAllocationEvent(LSRA_EVENT_NO_ENTRY_REG_ALLOCATED, currentInterval));
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