Yingwei Zheng 0a39c88e81 [InstCombine] Fold select Cond, not X, X into Cond ^ X (#93591) ...

See the following example:
```
define i1 @src(i64 %x, i1 %y) {
  %1526 = icmp ne i64 %x, 0
  %1527 = icmp eq i64 %x, 0
  %sel = select i1 %y, i1 %1526, i1 %1527
  ret i1 %sel
}

define i1 @tgt(i64 %x, i1 %y) {
  %1527 = icmp eq i64 %x, 0
  %sel = xor i1 %y, %1527
  ret i1 %sel
}
```
I find that this pattern is common in C/C++/Rust code base.
This patch folds `select Cond, Y, X` into `Cond ^ X` iff:
1. X has the same type as Cond
2. X is poison -> Y is poison
3. X == !Y

Alive2: https://alive2.llvm.org/ce/z/hSmkHS

2024-06-04 23:50:17 +08:00

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