This patch adds the support for and/or in `getFreelyInvertedImpl` using
DeMorgan's Law:
```
(~(A | B)) -> (~A & ~B)
(~(A & B)) -> (~A | ~B)
```
Alive2: https://alive2.llvm.org/ce/z/Uig8-j
Instructions in unreachable basic blocks are removed, but terminators
are not. In this case, even instructions that are only referenced by
a terminator, such as a return instruction, cannot be processed
properly.
This patch changes the operand of a return instruction in an
unreachable basic block to poison if it refers to the instruction,
allowing the instruction to be properly processed.
Fixes#65107.
If the and/or operand is an immediate constant, it will get folded
away anyway. Don't try to freely invert those operands.
A particularly degenerate case of this arises when both operands
are constant and the result is a constant, in which case we try
to invert users of a constant, resulting in an assertion failure.
Fixes https://github.com/llvm/llvm-project/issues/63791.
