For signed int-to-FP casts, ComputeNumSignBits can prove exactness where computeKnownBits cannot -- e.g. through ashr(shl x, a), b where sign propagation is tracked precisely but individual known bits are all unknown.
For signed int-to-FP casts, ComputeNumSignBits can prove exactness where computeKnownBits cannot -- e.g. through ashr(shl x, a), b where sign propagation is tracked precisely but individual known bits are all unknown.