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[InstCombine] canEvaluateShifted - remove dead (and never used code). NFC.

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This was already #if'd out when it was added back in 2010 at rG18d7fc8fc6767 and has never been touched since.
This commit is contained in:
Simon Pilgrim 2020-10-05 17:51:13 +01:00
parent bd755e5e2d
commit 606438d857
1 changed files with 0 additions and 25 deletions
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25
lib/Transforms/InstCombine/InstCombineShifts.cpp
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@ -481,31 +481,6 @@ static bool canEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// If this is the opposite shift, we can directly reuse the input of the shift
// if the needed bits are already zero in the input. This allows us to reuse
// the value which means that we don't care if the shift has multiple uses.
// TODO: Handle opposite shift by exact value.
ConstantInt *CI = nullptr;
if ((IsLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
(!IsLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
if (CI->getValue() == NumBits) {
// TODO: Check that the input bits are already zero with MaskedValueIsZero
#if 0
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
return CanEvaluateTruncated(I->getOperand(0), Ty);
}
#endif
}
}
// We can't mutate something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return false;