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

This was already #if'd out when it was added back in 2010 at rG18d7fc8fc6767 and has never been touched since.

Author: RKSimon

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -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;