This patch ensures the correct minimum bit width during type-shrinking. Previously when type-shrinking, we always sign-extended values back to their original width. However, if we are going to sign-extend, and the sign bit is unknown, we have to increase the minimum bit width by one bit so the sign-extend will fill the upper bits correctly. If the sign bit is known to be zero, we can perform a zero-extend instead. This should fix PR31243.