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JIT: enhance RBO inference for similar compares to constants #111766

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Jan 25, 2025
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JIT: enhance RBO inference for similar compares to constants #111766

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JIT: enhance RBO inference for similar compares to constants
AndyAyersMS Jan 23, 2025
f627fcc
Merge branch 'main' into Fix111725
AndyAyersMS Jan 24, 2025
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22 changes: 13 additions & 9 deletions src/coreclr/jit/redundantbranchopts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -681,19 +681,21 @@ bool Compiler::optRelopTryInferWithOneEqualOperand(const VNFuncApp& domApp,
// BB4:
// return;

// Check whether the dominating compare being "false" implies the dominated compare is known
// Check whether the dominating compare being "true" or false" implies the dominated compare is known
// to be either "true" or "false".
RelopResult treeOperStatus = IsCmp2ImpliedByCmp1(GenTree::ReverseRelop(domOper), domCns, treeOper, treeCns);
if (treeOperStatus == RelopResult::Unknown)
RelopResult ifTrueStatus = IsCmp2ImpliedByCmp1(domOper, domCns, treeOper, treeCns);
RelopResult ifFalseStatus = IsCmp2ImpliedByCmp1(GenTree::ReverseRelop(domOper), domCns, treeOper, treeCns);

if ((ifTrueStatus == RelopResult::Unknown) && (ifFalseStatus == RelopResult::Unknown))
{
return false;
}

rii->canInfer = true;
rii->vnRelation = ValueNumStore::VN_RELATION_KIND::VRK_Inferred;
rii->canInferFromTrue = false;
rii->canInferFromFalse = true;
rii->reverseSense = treeOperStatus == RelopResult::AlwaysTrue;
rii->canInferFromTrue = (ifTrueStatus != RelopResult::Unknown);
rii->canInferFromFalse = (ifFalseStatus != RelopResult::Unknown);
rii->reverseSense = (ifFalseStatus == RelopResult::AlwaysTrue) || (ifTrueStatus == RelopResult::AlwaysFalse);
return true;
}

Expand Down Expand Up @@ -832,10 +834,12 @@ bool Compiler::optRedundantBranch(BasicBlock* const block)
//
if (domIsInferredRelop)
{
// This inference should be one-sided
// We used to assert rii.canInferFromTrue ^ rii.canInferFromFalse here.
//
// But now we can find fully redundant compares with different relops,
// eg LT x, 47 dominating LE x, 46. The second relop's value is equal to the first.
//
assert(rii.canInferFromTrue ^ rii.canInferFromFalse);
JITDUMP("\nDominator " FMT_BB " of " FMT_BB " has same VN operands but different relop\n",
JITDUMP("\nDominator " FMT_BB " of " FMT_BB " can infer value of dominated relop\n",
domBlock->bbNum, block->bbNum);
}
else
Expand Down
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