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JIT: Transform floating SELECT(a < b, a, b) to NativeMin(a, b) #128402

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JIT: Transform floating SELECT(a < b, a, b) to NativeMin(a, b) #128402

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* add all possible SELECT(a < b, a, b) to nativeMin(a, b) transforms
BoyBaykiller May 20, 2026
75cee7e
* format
BoyBaykiller May 20, 2026
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60 changes: 57 additions & 3 deletions src/coreclr/jit/ifconversion.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@ class OptIfConversionDsc
GenTree* TrySelectToCnsOpCond(GenTreeConditional* select);
GenTree* TrySelectToLclOpCond(GenTreeConditional* select);
GenTree* TrySelectToCondOpLcl(GenTreeConditional* select);
GenTree* TrySelectToMinMax(GenTreeConditional* select);

#ifdef DEBUG
void IfConvertDump();
Expand Down Expand Up @@ -205,7 +206,7 @@ bool OptIfConversionDsc::IfConvertCheckStmts(BasicBlock* block, IfConvertOperati
}

// Ensure the operation has integer type.
if (!varTypeIsIntegralOrI(tree))
if (!varTypeIsIntegralOrI(tree) && !varTypeIsFloating(tree))
{
return false;
}
Comment on lines 208 to 212
Expand Down Expand Up @@ -636,14 +637,20 @@ bool OptIfConversionDsc::optIfConvert(int* pReachabilityBudget)
}
}

#ifdef TARGET_RISCV64
if (select->OperIs(GT_SELECT))
{
#ifdef TARGET_RISCV64
JITDUMP("Skipping if-conversion that could not be optimized to ordinary operations\n");
return true;
}
#endif
Comment on lines 640 to 645
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@BoyBaykiller BoyBaykiller May 20, 2026

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we call gtNewConditionalNode before which counts as change


// We only produce float SELECTs for optimization into non-SELECTs, otherwise bail
if (varTypeIsFloating(select))
{
return true;
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}
}

// Use the SELECT as the source of the Then STORE/RETURN.
m_thenOperation.node->AddAllEffectsFlags(select);
if (m_mainOper == GT_STORE_LCL_VAR)
Expand Down Expand Up @@ -739,6 +746,12 @@ GenTree* OptIfConversionDsc::TryOptimizeSelect(GenTreeConditional* select)
return opt;
}

opt = TrySelectToMinMax(select);
if (opt != nullptr)
{
return opt;
}

return nullptr;
}

Expand Down Expand Up @@ -960,6 +973,47 @@ GenTree* OptIfConversionDsc::TrySelectToCondOpLcl(GenTreeConditional* select)
return nullptr;
}

GenTree* OptIfConversionDsc::TrySelectToMinMax(GenTreeConditional* select)
{
#ifdef TARGET_XARCH
GenTree* condInput = select->gtCond;
GenTree* trueInput = select->gtOp1;
GenTree* falseInput = select->gtOp2;

if (!varTypeIsFloating(select) || !varTypeIsFloating(condInput->gtGetOp1()) ||
!varTypeIsFloating(condInput->gtGetOp2()))
{
return nullptr;
}

GenCondition cond = GenCondition::FromFloatRelop(condInput);
if (cond.IsUnordered() || !cond.Is(GenCondition::Code::FLT, GenCondition::Code::FGT))
{
return nullptr;
}

bool isMax = cond.Is(GenCondition::Code::FGT);
bool reversed = !GenTree::Compare(trueInput, condInput->gtGetOp1());
if (reversed)
{
// 'return a > b ? b : a;' has a GT but computes the min
isMax = !isMax;
std::swap(trueInput, falseInput);
}

if (GenTree::Compare(trueInput, condInput->gtGetOp1()) &&
GenTree::Compare(falseInput, condInput->gtGetOp2()->gtEffectiveVal()))
{
return m_compiler->gtNewSimdMinMaxNativeNode(select->TypeGet(),
reversed ? condInput->gtGetOp2() : condInput->gtGetOp1(),
reversed ? condInput->gtGetOp1() : condInput->gtGetOp2(),
select->TypeGet(), 0, isMax);
}

#endif
return nullptr;
}

//-----------------------------------------------------------------------------
// optIfConversion: If conversion
//
Expand Down
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