[llvm] [LLVM] Improve the DemandedBits Analysis (PR #148853)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw commented:

Can you provide the alive2 proof? See also https://llvm.org/docs/InstCombineContributorGuide.html#proofs.
You can use an extra integer parameter as the source of garbage bits:
```
define i32 @src(i32 %x, i32 %y, i32 noundef %z) {
  %div = udiv i32 %x, %y
  ret i32 %div
}
define i32 @tgt(i32 %x, i32 %y, i32 noundef %z) {
  %demanded_mask = ...
  %demanded_mask_inv = xor %demanded_mask, -1
  %x_demanded = and i32 %x, %demanded_mask
  %x_garbage = and i32 %z, %demanded_mask_inv
  %x_new = or disjoint %x_demanded, %x_garbage
  %div = udiv i32 %x_new, %y
  ret i32 %div
}
```

https://github.com/llvm/llvm-project/pull/148853