316c076694
This PR fixes a bug in combineX86CloadCstore where an optimization was
being applied too broadly, causing incorrect code generation.
Without any assumptions about `X` this transformation is only valid when
`Y` is a non zero power of two/single-bit mask.
```cpp
// res, flags2 = sub 0, (and (xor X, -1), Y)
// cload/cstore ..., cond_ne, flag2
// ->
// res, flags2 = sub 0, (and X, Y)
// cload/cstore ..., cond_e, flag2
```
We can restrict the optimization to most important case, so only apply
when `llvm::isOneConstant(Op1.getOperand(1))`. It might be not trivial
to find code that creates a SelectionDag with other values of `Y`.
Basline test: https://github.com/llvm/llvm-project/pull/163354
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