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JIT: Narrow long comparisons of sign-extended ints to int in VN #129148

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JIT: Narrow long comparisons of sign-extended ints to int in VN #129148

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20 changes: 18 additions & 2 deletions src/coreclr/jit/valuenum.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2052,9 +2052,13 @@ ValueNum ValueNumStore::VNIgnoreIntToLongCast(ValueNum vn)
var_types castToType;
bool srcIsUnsigned;
GetCastOperFromVN(castInfoVN, &castToType, &srcIsUnsigned);
if ((castToType == TYP_LONG) && !srcIsUnsigned && TypeOfVN(srcVN) == TYP_INT)
if ((genActualType(castToType) == TYP_LONG) && (TypeOfVN(srcVN) == TYP_INT))

@tannergooding tannergooding Jun 9, 2026

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Is genActualType(castToType) doing anything? Isn't that just TYP_ULONG -> TYP_LONG, in which case varTypeIsLong(castToType) is preferred?

@EgorBo EgorBo Jun 9, 2026

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Is genActualType(castToType) doing anything? Isn't that just TYP_ULONG -> TYP_LONG, in which case varTypeIsLong(castToType) is preferred?

Yep, pretty much the same as varTypeIsLong, will fix as part of some otherchange if no other fixes needed here

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{
return srcVN;
// A zero-extending cast preserves the sign-extended value only when the source is non-negative.
if (!srcIsUnsigned || IsVNNeverNegative(srcVN))
{
return srcVN;
}
}
}

Expand Down Expand Up @@ -5273,6 +5277,18 @@ ValueNum ValueNumStore::EvalUsingMathIdentity(var_types typ, VNFunc func, ValueN
return resultVN; // return the unsuccessful value
}

// Narrow "(long)x <cmp> (long)y" to an int comparison when both operands are just
// sign-extended ints; only TYP_INT comparisons feed assertion prop / bounds checks.
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if (VNFuncIsComparison(func) && (TypeOfVN(arg0VN) == TYP_LONG) && (TypeOfVN(arg1VN) == TYP_LONG))
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{
ValueNum newArg0VN = VNIgnoreIntToLongCast(arg0VN);
ValueNum newArg1VN = VNIgnoreIntToLongCast(arg1VN);
if ((TypeOfVN(newArg0VN) == TYP_INT) && (TypeOfVN(newArg1VN) == TYP_INT))
{
return VNForFunc(TYP_INT, func, newArg0VN, newArg1VN);
}
}

ValueNum cnsVN = NoVN;
ValueNum opVN = NoVN;

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