Back out r62958 from the release branch.

  }

  // We need at least W + T bits for the multiplication step

  unsigned CalculationBits = W + T;

  // FIXME: A temporary hack; we round up the bitwidths

  // to the nearest power of 2 to be nice to the code generator.

  unsigned CalculationBits = 1U << Log2_32_Ceil(W + T);

  // FIXME: Temporary hack to avoid generating integers that are too wide.

  // Although, it's not completely clear how to determine how much

  // widening is safe; for example, on X86, we can't really widen

  // beyond 64 because we need to be able to do multiplication

  // that's CalculationBits wide, but on X86-64, we can safely widen up to

  // 128 bits.

  if (CalculationBits > 64)

    return new SCEVCouldNotCompute();

  // Calcuate 2^T, at width T+W.

  APInt DivFactor = APInt(CalculationBits, 1).shl(T);