0ab4458df0
Fold
``` llvm
define i64 @src(i64 %50) {
%52 = lshr i64 -1, %50
%53 = add i64 %52, 1
%54 = call i64 @llvm.cttz.i64(i64 %53, i1 false)
ret i64 %54
}
```
to
``` llvm
define i64 @tgt(i64 %50) {
%52 = sub i64 64, %50
ret i64 %52
}
```
as
https://github.com/llvm/llvm-project/pull/91171#pullrequestreview-2040663002
pointed out.
Alive2 proof: https://alive2.llvm.org/ce/z/2aHfYa
Note: the `ctlz` version of this pattern seems not exist in dtcxzyw's
benchmark, so put it aside for now.