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Fold "new T[size].Length" into "size" #114845

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Merged
merged 1 commit into from
Apr 22, 2025
Merged

Fold "new T[size].Length" into "size" #114845

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31 changes: 31 additions & 0 deletions src/coreclr/jit/valuenum.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2610,6 +2610,37 @@ ValueNum ValueNumStore::VNForFunc(var_types typ, VNFunc func, ValueNum arg0VN)
{
*resultVN = VNForIntCon(knownSize);
}

// Case 4: ARR_LENGTH(new T[(long)size]) -> size
VNFuncApp newArrFuncApp;
if (GetVNFunc(arg0VN, &newArrFuncApp) && (newArrFuncApp.m_func == VNF_JitNewArr))
{
ValueNum actualSizeVN = newArrFuncApp.m_args[1];
var_types actualSizeVNType = TypeOfVN(actualSizeVN);

// JitNewArr's size argument (args[1]) is typically upcasted to TYP_LONG via VNF_Cast.
if (actualSizeVNType == TYP_LONG)
{
VNFuncApp castFuncApp;
if (GetVNFunc(actualSizeVN, &castFuncApp) && (castFuncApp.m_func == VNF_Cast))
{
var_types castToType;
bool srcIsUnsigned;
GetCastOperFromVN(castFuncApp.m_args[1], &castToType, &srcIsUnsigned);

// Make sure we have exactly (TYP_LONG)myInt32 cast:
if (!srcIsUnsigned && (castToType == TYP_LONG) && TypeOfVN(castFuncApp.m_args[0]) == TYP_INT)
{
// If that is the case, return the original size argument
*resultVN = castFuncApp.m_args[0];
}
}
}
else if (actualSizeVNType == TYP_INT)
{
*resultVN = actualSizeVN;
}
}
}

// Try to perform constant-folding.
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